Specification
BepiColombo
Change Record
Issue
1
2
Doc. No:
Issue:
Date
15.02.07
06.08.07
Sheet
all
all
BC-ASD-SP-00016
2
Description of Change
first issue for SRR Data Package
Second issue, completely restructured and reworked:
• Usage of Mode-Codes and Status Word Bits
• Framing Scheduling
• Time Synchronisation
• Data/Block Transfer Protocol
• Mil-Bus FDIR
Release
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Specification
BepiColombo
Table of Contents
1
1.1
1.2
1.3
1.4
1.5
INTRODUCTION..................................................................................................................8
Scope .....................................................................................................................................8
Objective of Document........................................................................................................9
Summary Description .......................................................................................................10
Acronyms & Abbreviations ..............................................................................................11
Definitions of Terms ..........................................................................................................12
2
DOCUMENTS......................................................................................................................14
2.1 Applicable Documents.......................................................................................................14
2.2 Applicable Standards ........................................................................................................14
2.3 Reference Documents ........................................................................................................14
3
PHYSICAL LAYER ............................................................................................................15
3.1 Bit and Field Numbering Conventions ............................................................................15
3.2 BepiColombo MIL-STD-1553B Bus Topology ...............................................................15
3.3 Physical Level Requirements............................................................................................17
4
DATA LINK LAYER ..........................................................................................................18
4.1 Bus Controller Functions and Operation........................................................................18
4.2 Remote Terminal Functions .............................................................................................19
4.2.1 RT Initialisation .......................................................................................................19
4.3 Message and Word Formats.............................................................................................20
4.3.1 Command Word.......................................................................................................20
4.3.1.1 Remote Terminal Address Field ..........................................................................20
4.3.1.2 Transmit/Receive (T/R) Bit Field ........................................................................22
4.3.1.3 Subaddress / Mode Field.......................................................................................22
4.3.1.4 Data Word Count / Mode Code Field..................................................................26
4.3.2 Data Words...............................................................................................................32
4.3.3 Status Words ............................................................................................................32
4.3.3.1 Message Error Bit .................................................................................................33
4.3.3.2 Instrumentation Bit...............................................................................................34
4.3.3.3 Service Request Bit................................................................................................34
4.3.3.4 Broadcast Command Received Bit ......................................................................35
4.3.3.5 Busy Bit ..................................................................................................................35
4.3.3.6 Subsystem Flag Bit ................................................................................................36
4.3.3.7 Dynamic Bus Control Acceptance Bit .................................................................36
4.3.3.8 Terminal Flag Bit ..................................................................................................37
4.3.3.9 Status Word Reset/Update ...................................................................................37
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5
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
6
TRANSFER LAYER ...........................................................................................................38
Message Formats and Timing ..........................................................................................38
5.1.1 BC to RT Data Message (Receive Message) ..........................................................39
5.1.2 RT to BC Data Message (Transmit Message) .......................................................40
5.1.3 Mode Command without Data Word Message .....................................................40
5.1.4 Mode Command with Data Word from RT Message...........................................41
5.1.5 Mode Command with Data Word from BC Message...........................................41
5.1.6 Broadcast BC to RT Command Message ..............................................................42
5.1.7 Broadcast Mode Command with Data Word from BC Message ........................42
5.1.8 Message Timing Requirements...............................................................................43
5.1.9 Message Validation ..................................................................................................44
5.1.10 Max Busy Bit Set Times ........................................................................................44
5.1.11 Data Wrap-Around................................................................................................45
General Requirements ......................................................................................................45
5.2.1 Communication with Non-Packet Terminals........................................................45
5.2.2 Communication with PUS-Packet Terminals and MMO ....................................46
Frame Scheduling..............................................................................................................47
5.3.1 Frame Timing...........................................................................................................49
5.3.2 Frame Synchronisation ...........................................................................................51
5.3.3 Frame Utilisation .....................................................................................................52
5.3.4 BC Message Sequence Control ...............................................................................54
5.3.5 Bus Loading..............................................................................................................55
Time Synchronisation .......................................................................................................56
5.4.1 Synchronise Mode Command Procedure ..............................................................57
5.4.2 PPS-based Synchronisation Procedure..................................................................58
Block Transfer Protocol....................................................................................................58
5.5.1 General......................................................................................................................58
5.5.2 BC to RT Block Transfer (Command Distribution).............................................61
5.5.3 RT to BC Block Transfer (Data Acquisition)........................................................63
Event Data Acquisition .....................................................................................................65
Commanding and Data Acquisition of Non-Packet Terminals.....................................68
5.7.1 MPO-PCDU, MTM-PCDU, DST, MORE (tbc) and BERM (tbc) ......................68
5.7.2 MPO-SADE, MTM-SADE and APME (HGA & MGA) ......................................70
5.7.3 IMU ...........................................................................................................................72
5.7.4 MPCU-CPS-I/O (TBC)............................................................................................73
Commanding and Data Acquisition of PUS-Packet Terminals ....................................75
Commanding and Data Acquisition of MMO.................................................................77
5.9.1 MMO Telemetry Acquisition..................................................................................77
5.9.2 MMO Commanding.................................................................................................79
MIL-BUS FDIR (TBC)........................................................................................................81
6.1 Error Processing on BC Hardware Level .......................................................................81
6.2 Error Processing on BC Software Level .........................................................................83
6.3 Mil-Bus Failure Isolation Procedure ...............................................................................84
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BepiColombo
List of Figures
Figure 3.2-1: BepiColombo MIL-STD-1553B Bus System Topology.......................... 16
Figure 4.3-1: MIL-STD-1553B Word Types & Formats............................................... 20
Figure 4.3-2: Transmit Vector Word Transfer ............................................................... 30
Figure 5.1-1: Information Transfer Formats .................................................................. 38
Figure 5.1-2: Broadcast Information Transfer Formats ................................................. 39
Figure 5.1-3: BC to RT Data Message Format and Timing........................................... 39
Figure 5.1-4: RT to BC Data Message Format and Timing........................................... 40
Figure 5.1-5: Mode Command without Data Word Message Format and Timing ........ 40
Figure 5.1-6: Mode Command with Data Word from RT Message Format and Timing41
Figure 5.1-7: Mode Command with Data Word from BC Message Format and Timing41
Figure 5.1-8: Broadcast BC to RT(s) Data Message Format and Timing ..................... 42
Figure 5.1-9: Broadcast Mode Command with Data Word Message Format and Timing42
Figure 5.3-1: Mil-Bus Scheduling (Major Frame / Minor Frame / Message Slot) ........ 48
Figure 5.5-1: Block Transfer Descriptor Words ............................................................ 60
Figure 5.5-2: BC to RT Block Transfer (simplified) ..................................................... 61
Figure 5.5-3: RT to BC Block Transfer (simplified) ..................................................... 63
Figure 6.2-1: Recovery as a Function of 1553B Error Conditions ................................ 84
Figure 6.3-1: Mil-Bus Failure Isolation procedure (simplified) .................................... 85
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List of Tables
Table 4.3-1: RT Address Allocation .............................................................................. 21
Table 4.3-2: Sub-Addresses Allocation for BepiColombo ............................................ 23
Table 4.3-3: MIL-STD-1553B Mode Code Requirements for BepiColombo ............... 27
Table 4.3-4: Vector Word Format for Aperiodic Message Demand from RT............... 31
Table 4.3-5: Vector Word Format for Aperiodic Action Demand from RT.................. 31
Table 4.3-6: Status Word Bit usage for BepiColombo .................................................. 33
Table 5.3-1: MPO Framing/Phasing Requirements (TBC)............................................ 53
Table 5.3-2: MTM Framing/Phasing Requirements (TBC)........................................... 54
Table 5.3-3: MMO Framing/Phasing Requirements (TBC) .......................................... 54
Table 5.4-1: RT Synchronisation Procedure Allocation ................................................ 56
Table 5.4-2: MIL-STD-1553B SCET Distribution Format ........................................... 57
Table 5.7-1: TM Data Trigger Command Word ............................................................ 69
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1
BepiColombo
Introduction
BepiColombo is an Interdisciplinary Cornerstone Mission to the planet Mercury, in collaboration
between ESA and ISAS/JAXA of Japan. It consists of two scientific orbiters, the Mercury
Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO), which are dedicated
to the detailed study of the planet and of its magnetosphere.
The mission will commence in 2013 with the launch of the Mercury Composite Spacecraft
(MCS) on Soyuz Fregat. Following a long interplanetary cruise, powered by the Mercury
Transfer Module (MTM), the Mercury Planetary Orbiter (MPO) and the Mercury
Magnetospheric Orbiter (MMO) will be delivered to their planetary orbits in 2019. The nominal
mission will be completed by the end of 2020 with a possible extension of one more year.
The key challenges of the mission are to provide a safe transfer of the spacecraft carrying the
scientific instruments to Mercury and to ensure successful science operations of both orbiters
under extreme environmental conditions.
1.1
Scope
Based on the applicable MIL-STD-1553B Notice 4 standard [SD-1], this specification comprises
the contractually relevant requirements and constraints for the BepiColombo command/control
data communications bus.
This includes:
•
The performance requirements of subject hardware and software.
•
The design and interface requirements of the MIL-STD-1553B system.
•
The testing and verification requirements.
This specification covers the MIL-STD-1553B protocol extensions (network, transport, and
service layers) in order to give comprehensive requirements specification of the MIL-STD1553B system necessary for the BepiColombo mission.
Requirements within this document are shown in an italic font. Each requirement is preceded by
a summary line that contains the following fields, delimited by "/".
•
Doors Requirement Number
•
Created From
•
Verification Method
The Doors Requirement Number has the form "BUS-xxx" where xxx is a unique number
assigned consecutively.
The Created From field shows the parent requirement or "Created" if the requirement is created
at this level.
The Verification Method codes are as follows:
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Specification
•
D - Definition
•
S - Similarity
•
R - Review
•
A - Analysis
•
I - Inspection
•
T - Test
BepiColombo
If tables are considered as part of the requirement they are referenced clearly in the text and
inserted after and separated from the requirement table and are managed as free text attached to
the identifier requirement.
The trace to the upper level requirements (Upper Links), shall be managed using the following
format:
•
AAA-NNN where AAA is a label assocoated to the upper document and NNN the
requirement identifier of this upper level.
•
or CREATED keyword if the requirement has no link with upper level.
All document elements not presented in the format explained above are not requirements and
will not be verified or tracked.
1.2
Objective of Document
The document in hand is the basis for the design of all BepiColombo MCS units connected to the
MPO-, MTM- and MMO-MIL-STD-1553B-bus which are used as common serial data busses
for communication between the OBC, executing the Central Software (CSW), and the
•
STR-1, STR-2, STR-3, IMU, BERM, MPO-PCDU, MPO-SADE, APME, DST-1, DST2, KaT (MORE)
•
MTM-PCDU, MTM-SADE, MPCU (MEPS and CPS-I/O)
•
MMO
The specification provides the applicability of the requirements to the following BepiColombo
items:
•
On-board Computer (OBC) that is the unique Bus Controller (BC) within the
BepiColombo MIL-STD-1553B system. The OBC provides the physical/signal and the
data link layers and supports the network layer.
•
Central Software (CSW) that executes the higher levels of protocol on the BC side.
•
Mil-Bus Terminals (RT) defined as PUS-Packet Terminals which receive packets from
and send packets to the BC.
•
Mil-Bus Terminals (RT) defined as Packet Terminal (MMO) which receive packets
from and send packets to the BC.
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•
Mil-Bus Terminals (RT) defined as Non-Packet Terminals which are adapted via lowlevel protocol based on Mil-Bus messages.
•
Harness that encompasses all the MPO, MTM, MMO cabling system elements from the
Bus Controller to all the Remote Terminals: connectors, cables, shields, couplers,
terminators, stubs.
The document comprises the contractually relevant technical requirements and constraints for
the MIL-STD-1553B data bus so enabling the different parties involved to design, develop and
test their part with respect to the common data bus.
Consequently the document establishes the performance as well as design and interface
requirements for the OBC as Bus Controller (BC), the Remote Terminals (RTs) and the Central
Software (CSW).
The conceptual basis of this document is the establishment of a MIL-1553B protocol for
BepiColombo with a complexity as low as possible but fulfilling all higher level system
requirements. This is aimed to suport cost-saving and flawless implementation on the one hand,
and straight forward verification on the other hand. The following rules have been obeyed:
•
The protocol omits using all of the features available in the MIL-STD-1553B [SD-1].
E.g. only those bits from the status word have been selected which provide essential
information to the bus controller.
•
A high degree of determinism is pursued.
•
No auto-retry on the protocol level is foreseen (TBC). This is due to the experience that
random errors on the MIL-Bus are very rare and persistent errors require system FDIR
measures.
1.3
Summary Description
This document includes all technical requirements to the specified MIL-STD-1553B items.
•
Chapter 1 includes definitions, lists of acronyms and abbreviations.
•
Chapter 2 lists references to related documents and standards.
•
Chapter 3 provides definition of physical level incl. Bus-Topology and bit/field
numbering conventions.
•
Chapter 4 specifies the data link layer requirements: BC and RT function, Message and
Word formats providing physical addressing and use of Mode-commands and Status
Word bits.
•
Chapter 5 specifies the Transfer layer requirements, which covers bus configuration,
transfer control requirements covering the transport of all anticipated profiles of 1553
messages, Frame scheduling and the synchronisation requirements.
•
Chapter 6 provides Mil-bus FDIR requirements.
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The BepiColombo On-Board Electrical System makes use of the MIL-STD-1553B bus
architecture.
For communication between the On-board Computer (OBC) with the various equipments and
Payload, the following dual redundant MIL-STD-1553B bus systems will be implemented
onboard BepiColombo:
•
MPO-1553B-Bus dedicated to the communications with MPO platform equipments (incl.
payloads KaTranslator, BERM)
•
MTM-1553B-Bus dedicated to the communications with the MTM platform equipments
•
MMO-1553B-Bus dedicated to the communications with the MMO (Payload)
This document defines all MIL-1553B-Bus interface protocol relevant requirements up to the
protocol extensions to properly use the bus on system level.
No electrical connection between these three Mil-Buses exists.
No functional connection between these three Mil-Buses exists within the scope of this protocol
specification.
As a result, the item designer finds all 1553 relevant requirements in this document plus in [SD1] and [SD-2].
The design and interface requirements on signal level of the MIL-STD-1553B system are
covered in chapter 3.6.4 of [AD-1] applying to
•
On-board Computer (OBC) as Bus Controller (BC)
•
Mil-Bus Terminals (RT) defined as PUS-Packet Terminals
•
Mil-Bus Terminals (RT) defined as Packet Terminal (MMO)
•
Mil-Bus Terminals (RT) defined as Non-Packet Terminals
•
Harness that encompasses all the MPO, MTM, MMO cabling system elements from the
Bus Controller to all the Remote Terminals: connectors, cables, shields, couplers,
terminators, stubs.
Data entities transferred to and from "Packet Terminals" are termed "block" for distinction from
PUS packets. The detailed structure of blocks is specified in this document.
Unless specific items require distinction of the three busses, all definitions and requirements
apply for all of them.
1.4
Acronyms & Abbreviations
APME
Antenna Pointing Mechanism Electronics
BC
(1553) Bus Controller
CPS-I/O
Chemical Propulsion Subsystem Input/Output
CSW
Central Software
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FDIR
Failure Detection, Isolation and Recovery
GDIR
General Design & Interface Requirements Specification
HK
Housekeeping
ICD
Interface Control Document
MEPS
Mercury Electric Propulsion Subsystem
MPCU
MTM Propulsion Control Unit
MMO
Mercury Magnetometer Orbiter
MPO
Mercury Planetary Orbiter
MTM
Mercury Transfer Module
MTL
Mission Timeline
OBC
On-board Computer
OBT
On-Board Time
PCDU
Power Control & Distribution Unit
RT
(1553) Remote Terminal
SA
Subaddress
SADE
Solar Array Drive Electronics
SCET
SpaceCraft Elapsed Time
STR
Star Tracker
TC
TeleCommand
TM
TeleMetry
DST
Deep SpaceTransponder
BepiColombo
1.5
Definitions of Terms
For general definitions and terms refer to [SD-1] and [SD-2].
In addition the following definition of terms and additional explanations apply:
Aperiodic: Events occurring at indefinite or unscheduled time periods. This term is used to
describe the timing of messages that are not assigned a regular transmission update rate.
“Asynchronous” is another word used to express the same condition.
Central Software: That software that is dedicated to spacecraft management, operations
execution, AOCS, payload management, data management, etc. This distinguishes Central
Software from the central computer (OBC) and its Basic Software providing basic Bus
Controller functionalities.
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Data Wrap-Around: Many RTs include a “data wrap-around” function, in which data words
sent to the RT with a receive command are send back to the bus controller with a subsequent
transmit command.
Fail-Safe Timer: MlL-STD-1553B requires (4.4.1.3 of 1553B) that every RT or BC contain a
hardware timer to prevent any transmission on the bus longer than 800 us. Since no valid
transmission is longer than 660 us, only a failure in the terminal could result in a transmission of
800 us or longer. The fail-safe timer is required to prevent such a failure from causing a
continuous transmission on the bus and thus rendering it (the bus) unusable for other
transmissions.
Frame Structure: The frame structure of the multiplex data bus consists of a major frame of
1second in duration which is composed of eight minor frames of 125 ms in duration.
Example of frame allocation: Within each minor frame, all data to be transmitted at a 8-Hz rate
are transmitted at the beginning of the frame. During each odd-numbered minor frame, following
the transmission of the 8-Hz data, all 4-Hz data transfers occur. During minor frames 4 and 8,
following transmission of the 8-Hz data, all 2-Hz data transmissions occur. All 1-Hz data
transmissions occur during minor frames 2 and 6, in order to evenly distribute the1-Hz data load.
The frame structure is specified, including major and minor frame times, and transfers to occur
in each of the frames. The specified structure accommodate the maximum update rates required
for time critical messages, while at the same time providing an adequate schedule reserve for
error recovery procedures, synchronization, aperiodic message traffic, and system growth.
Illegal Commands: A valid command that is not implemented in the receiving RT.
Message: In 1553 terms, a message is a part of an information transfer format, such as 1 to 32
data words. A message may also refer to the entire transmission by both bus controller and
responding remote terminal, which includes not only the data words but the overhead. This
second usage is more correctly called an information transfer format.
Mode Code: A means by which the bus controller can communicate with the multiplex-busrelated hardware in order to assist in the management of the information flow.
Mode Command: An information transfer format with the subaddress/mode field in the
command word set to indicate that the next following field is a mode code. An RT that
implements Mode Commands is required to know that a subaddress/mode field in a Command
Word equal to 00000 or 11111 defines a Mode Command, and that, in this case, the Word Count
field is to be treated as the Mode Code rather than the number of words.
Polling: This is the method of communicating with multiple terminals within a system to
determining information transfer priorities or servicing needs. RTs might be polled to determine
whether they have aperiodic or high priority messages to transmit, state of health, or capability
of accepting bus control.
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2
Documents
2.1
Applicable Documents
BepiColombo
BUS-23/Created/
[AD-1] BC-ASD-SP-00001, BepiColombo General Design and Interface Requirements (GDIR)
2.2
Applicable Standards
BUS-20/Created/
[SD-1] MIL-STD-1553B Notice IV, Digital Time Division Command/Response Multiplex Data
Bus.
BUS-21/Created/
[SD-2] MIL-HDBK-1553A Multiplex Applications Handbook, Department of Defense, that shall
be applied as follows:
•
Section 100: RT Validation Test Plan shall apply and Remote Terminal Contractors shall
use it to certify the conformance of their RTs.
•
All the other sections contain guidelines and examples.
2.3
Reference Documents
[RD-1] BC-ASD-IF-00019, BepiColombo Space-to-Ground Interface Control Document
(SGICD) Vol. 2 (Generic Packet Structure)
[RD-2] ECSS-E-70-41A, Telemetry and telecommand packet utilization, 30 January 2003
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3
BepiColombo
Physical Layer
3.1
Bit and Field Numbering Conventions
The general Bit numbering and priority conventions defined in [SD-1] are defined in [AD-1]
(GDI-2734, -2735).
BUS-409/Created/T
For 2-byte information, "byte 0" shall represent the most significant byte and "byte 1" the least
significant byte. "Byte 0" (starting from the left) shall be transmitted first.
BUS-410/Created/T
For 4-byte information, "byte 0" shall represent the most significant byte of the high order word,
the low order word shall start at "byte 2" with the least significant byte being "byte 3". "Byte 0"
(starting from the left) shall be transmitted first.
BUS-413/Created/T
For a 32-bit floating-point value, "byte 0" shall represent the byte containing the sign bit and the
exponent most significant bits, "byte 3" shall represent the least significant bits of the mantissa
(according to IEEE-STD-754).
BUS-414/Created/T
For a 64-bit floating-point value, "byte 0" shall represent the byte containing the sign bit and the
exponent most significant bits, "byte 7" shall represent the least significant bits of the mantissa
(according to IEEE-STD-754).
3.2
BepiColombo MIL-STD-1553B Bus Topology
The BepiColombo MIL-STD-1553B bus system/topology implements three separate, each dualredundant, data busses as shown in Figure 3.2-1:
•
one for the BepiColombo MPO,
•
one for the MTM and
•
one for the MMO.
BC and RT's are connected to the data bus through transformer coupled stubs.
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IMU
A
B
STR- STR- STR1
2
3
BERM
BepiColombo
MPO-PCDU MPO-SADE
A
B
A
APME
B
A
DST-1
DST-2
KaT
B
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
N R
N R
N R
N R
N R
N R
N R
N R
N R
N R
N R
N R
N R
N R
N R
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
N R
N R
MPO
BC
MPO
BC
MPO
1553B
C
-Bus
C
Z
C
N R
N R
C
C
Umbilical
Connectors
MMO
C
MMO 1553BBus
Z
C
C
C
C
C
C
C
C
N R
RT
N R
RT
N R
RT
N R
RT
N R
RT
N R
RT
N R
RT
N R
RT
A
B
A
B
A
B
A
B
RT
MTM
BC
C
N R
MTM
BC
MTM 1553BBus
Umbilical
Connectors
PM-B
N R
PM-A
C
N R
Test
MMO
BC
OBC
MMO
BC
Z
Z
Skin
Connectors
Z
C
Z
Test
CPS-I/O
MEPS
MTM-PCDU
Skin
Connectors
MTM-SADE
MPCU
Figure 3.2-1: BepiColombo MIL-STD-1553B Bus System Topology
BUS-276/Created/R
Each BepiColombo MIL-STD-1553B-bus system and participant shall be compliant to the
redundancy concept as defined in chapter 3.6.4 of [AD-1].
BUS-282/[SD-1]/T,R
Signals shall only be allowed to appear on one of the two 1553 Data Buses at a time.
Note: Failure recovery on higher software level will lead to switch over to redundant bus.
BUS-280/[SD-1]/T
The RT shall have the capability to distinguish on a message basis which of the redundant bus is
in use.
(Hence no dedicated discrete signal from BC to RTs shall be required for bus selection
designation between bus A and bus B.)
BUS-734/Created/T,R
No RT to RT Data Transfer shall be implemented.
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Specification
3.3
BepiColombo
Physical Level Requirements
The physical level requirements
•
electrical signal characteristics
•
cables, connectors, transformer-coupled stubs
•
RT address connector
•
shielding etc
for BepiColombo MIL-STD-1553B bus systems are defined in [AD-1] chapter 3.6.4.
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Specification
4
Data Link Layer
4.1
Bus Controller Functions and Operation
BepiColombo
BUS-733/Created/T
The (redundant) Onboard Computer (OBC) shall act as the Bus Controller (BC).
BUS-403/Created/T
The BC shall be able to send Mil-Bus messages to the units or instruments working as Remote
Terminals (RT) on the Mil-1553B-busses.
At least the following Mil-1553B-bus data transfer functions shall be provided:
•
BC to RT Data Transfer
•
RT to BC Data Transfer
•
Mode Command without Data Word
•
Mode Command with Data Word from RT (Transmit)
•
Mode Command with Data Word from BC (Receive)
•
Broadcast for frame synchronisation
BUS-281/[SD-1]/T
The BC shall have the capability to use either of the two buses for communication on message
basis.
This means that the BC shall have the capability to distinguish on a message basis which bus is
in use.
BUS-405/Created/T
The BC shall support the RT Subaddress Allocation as defined in section 4.3.1.3 of this
document
BUS-404/Created/T
The BC shall support Mode Commands as defined in section 4.3.1.4 with the corresponding
patterns.
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Specification
4.2
BepiColombo
Remote Terminal Functions
BUS-16/Created/T
All spacecraft units or instruments connected to the Mil-1553B-busses shall act as Remote
Terminals.
BUS-58/Created/T
All RTs shall operate in response to valid commands received from the BC.
BUS-59/Created/T
No RT shall speak on the 1553 Data Bus unless spoken to first by the BC and specifically
commanded to transmit.
BUS-94/Created/T
Each RT shall support the RT Subaddress Allocation as defined in section 4.3.1.3 of this
document.
BUS-84/Created/T
The RTs shall support Mode Commands as defined in section 4.1.4.4 with the corresponding
patterns.
BUS-128/Created/T,R
RTs shall support broadcast messages.
4.2.1
RT Initialisation
BUS-273/[SD-1]/T
Remote terminals shall sample the terminal address wires during power-on or reset.
BUS-272/[SD-1]/T
The RT shall perform a parity test upon the wired terminal address. Odd parity shall be used in
checking the parity of the wired terminal address. Further details are defined in chapter 3.6.4 of
[AD-1].
BUS-274/[SD-1]/T
If the parity of the wired terminal address is found incorrect, the terminal shall stop
initialisation and no command messages shall be responded.
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Specification
BepiColombo
4.3
Message and Word Formats
The MIL-STD-1553B word formats - Command Word, Data Word and Status Word - as defined
in [SD-1] and applied by [AD-1] are recalled in Figure 4.3-1:
Figure 4.3-1: MIL-STD-1553B Word Types & Formats
BUS-743/[SD-1]/T
Word Validation shall be implemented as defined in [SD-1], section 4.4.1.1.
Note: A command word, which fulfills the above criteria, is declared valid but might be declared
illegal if it is operationally wrong.
4.3.1
Command Word
The Command Word is defined in [SD-1] and applied by [AD-1].
4.3.1.1 Remote Terminal Address Field
Each RT connected to a Mil-1553B-bus has a unique address which allows the BC to
communicate with the selected equipment. The address 0 is reserved, address 31 is used for
broadcast.
The RT Address shall be configurable via an exernal connector of the RT equipment as required
by [AD-1], para. 3.6.4.7.
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Specification
BepiColombo
BUS-86/[SD-1]/T
The Remote Terminal Address field shall be used to address the required RT in accordance with
[SD-1].
BUS-268/Created/T
The RT address allocation for BepiColombo shall be as defined in Table 4.3-1 (TBC).
RT Address Parity
[hex (dec)]
Bit
00000 (0)
00001 (1)
00010 (2)
00011 (3)
00100 (4)
00101 (5)
00110 (6)
00111 (7)
01000 (8)
01001 (9)
01010 (10)
01011 (11)
01100 (12)
01101 (13)
01110 (14)
01111 (15)
10000 (16)
10001 (17)
10010 (18)
10011 (19)
10100 (20)
10101 (21)
10110 (22)
10111 (23)
11000 (24)
11001 (25)
11010 (26)
11011 (27)
11100 (28)
11101 (29)
11110 (30)
11111 (31)
1
0
0
1
0
1
1
0
0
1
1
0
1
0
0
1
0
1
1
0
1
0
0
1
1
0
0
1
0
1
1
0
MPO-1553Bbus RT
MTM-1553Bbus RT
MMO-1553Bbus RT
reserved
reserved
reserved
MPO-PCDU_A
MPO-PCDU_B
MPO-SADE_A
MPO-SADE_B
APME_A
APME_B
MTM-PCDU_A
MTM-PCDU_B
MTM-SADE_A
MTM-SADE_B
MPCU_MEPS_A
MPCU_MEPS_B
MPCU_CPS_A
MPCU_CPS_B
MMO A
MMO B
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
DST-1
DST-2
KaT (MORE)
BERM
IMU A
IMU B
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
STE-1
STE-2
STE-3
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
reserved
common
address for
broadcast
common
address for
broadcast
common
address for
broadcast
Table 4.3-1: RT Address Allocation
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Specification
BepiColombo
4.3.1.2 Transmit/Receive (T/R) Bit Field
BUS-89/[SD-1]/T
The usage of the Transmit/Receive (T/R) bit shall be in accordance to [SD-1], para 4.3.3.5.1.3.
Transmit/Receive (T/R) bit defines the action required from the RT:
•
T/R bit set to logical 0 indicates that the RT shall receive data from the BC
•
T/R bit set to logical 1 indicates that the RT shall transmit data to the BC
4.3.1.3 Subaddress / Mode Field
BUS-91/Created/T
The allocation of subaddresses shall be as defined in Table 4.3-2 (TBC).
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Specification
Subaddress (SA)
Dec
Bin
0
00000
1
00001
2
00010
3
00011
4
00100
5
00101
6
00110
7
00111
8
01000
9
01001
10
01010
11
01011
12
01100
13
01101
14
01110
15
01111
16
10000
17
10001
18
10010
19
10011
20
10100
21
10101
22
10110
23
10111
24
11000
25
11001
26
11010
27
11011
28
11100
29
11101
30
11110
31
11111
RT to Transmit [T]
T/R-bit = 1
Reserved for Mode Commands
TM Data buffer 1
TM Data buffer 2
TM Data buffer 3
TM Data buffer 4
TM Data buffer 5
TM Data buffer 6
TM Data buffer 7
TM Data buffer 8
TM Data buffer 9
TM Data buffer 10
TM Data buffer 11
TM Data buffer 12
TM Data buffer 13
TM Data buffer 14
TM Data buffer 15
TM Data buffer 16
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Health Status from RT
Event message data buffer
Event Request (TBD)
Reserved
TM Data Transfer Request
TC Data Transfer Confirmation
Data Wrap-around Read
Reserved for Mode Commands
BepiColombo
RT to Receive [R]
T/R-bit = 0
Reserved for Mode Commands
TC Data buffer 1
TC Data buffer 2
TC Data buffer 3
TC Data buffer 4
TC Data buffer 5
TC Data buffer 6
TC Data buffer 7
TC Data buffer 8
TC Data buffer 9
TC Data buffer 10
TC Data buffer 11
TC Data buffer 12
TC Data buffer 13
TC Data buffer 14
TC Data buffer 15
TC Data buffer 16
Reserved
Reserved
Reserved
Reserved
Reserved
TM Data Trigger Command
Reserved
Health Status from BC
Reserved
Event Confirmation (TBD)
Time (SCET) message from OBC
TM Data Transfer Confirmation
TC Data Transfer Request
Data Wrap-around Write
Reserved for Mode Commands
Table 4.3-2: Sub-Addresses Allocation for BepiColombo
The subaddresses shall be used as described below:
BUS-98/Created/T
Mode Command (SA 0, 31)
The use of subaddress 0 and 31 (dec) shall be according to [SD-1].
BUS-420/Created/T
TM Data Send (SA 1 - 16 T)
This subadress(es) shall comprise the nominal Telemetry data. The MSByte shall be transmitted
first.
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Specification
BepiColombo
BUS-811/Created/T
TC Data Receive (SA 1 - 16 R)
This subadress(es) shall comprise the nominal Telecommand data. The MSByte shall be
transmitted first.
BUS-812/Created/R
Reserved (SA 17 - 23 T, 27 T)
Unused transmit SA.
BUS-813/Created/R
Reserved (SA 17 - 21 R, 23 R, 25 R)
Unused receive SA.
BUS-889/Created/T
TM Data Trigger Command from BC (SA 22 R)
The BC shall provide via this SA a trigger command to dedicated RTs for starting the
preparation of their periodic Housekeeping Data to be acquired in the fixed section of the
subsequent Minor Frame allocated.
BUS-814/Created/T
Health Status from RT (SA 24 T)
Via this SA the RT shall provide HK-Data and status data about the RT unit (TBC).
BUS-815/Created/T
Health Status from BC (SA 24 R)
To be defined.
BUS-816/Created/T
Event Message Data (SA 25 T)
To be defined.
BUS-817/Created/T
Event Request (SA 26 T)
To be defined.
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BepiColombo
BUS-818/Created/T
Event Confirmation (SA 26 R)
To be defined.
BUS-819/Created/T
Time (SCET) Message (SA 27 R)
To be defined.
BUS-820/Created/T
TM Packet Transfer Request (SA 28 T)
The RT shall provide via this SA the request for a TM Packet transfer.
BUS-821/Created/T
TM Packet Transfer Confirmation from BC (SA 28 R)
The BC shall provide via this SA the confirmation for a TM Packet transfer to the RT.
BUS-822/Created/T
TC Packet Transfer Confirmation from RT (SA 29 T)
The RT shall provide via this SA the confirmation for a TC Packet transfer to the BC.
BUS-823/Created/T
TC Packet Transfer Request from RT (SA 29 R)
The BC shall provide via this SA the request for a TC Packet transfer to the RT.
BUS-824/[SD-1]/T
Data Wrap-around Read (SA 30 T)
This SA shall be used for implementation of Data Wrap-around (transmit) as specified in [SD-1,
Not.II §30.7].
BUS-825/[SD-1]/T
Data Wrap-around Write (SA 30 R)
This SA shall be used for implementation of Data Wrap-around (receive) as specified in [SD-1,
Not.II §30.7]
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Specification
BepiColombo
BUS-826/Created/R
Subaddress Allocation for non-intelligent Remote Terminals (Non-Packet-RTs):
For non-intelligent Remote Terminals (which do not handle TM/TC-Packets) the same
Subaddresses as for Packet-RTs shall be used for standardized functionalities.
4.3.1.4 Data Word Count / Mode Code Field
The Data Word Count Field indicates the quantity of data words to be transferred to/ from the
BC.
To be used as defined by to [SD-1] § 4.3.3.5.1.5. as required by [AD-1].
Mode codes are defined by the standard to provide the Bus Controller (BC) with data bus
management and error processing / recovery capability. Mode Codes are with a data word, other
mode codes are without data word. The mode codes are defined by bit positions 15-19 of the
Command Word. The most significant bit (bit 15) can be used to differentiate between the two
mode code groups. When a data word is associated with the mode code, the Transmit/Receive
(T/R) bit of the Command Word determines if the data word is transmitted or received by the
RT.
BUS-101/Created]/T
In case the Subaddress Field is set to '00000' or '11111' the BC and RTs shall support Mode
Code Commands as defined in Table 4.3-3.
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Specification
BepiColombo
Assoc.
Data
Word
Broadcast
allowed
BepiColombo
BC/RT
Applicability
Dynamic Bus Control
(not implemented / illegal)
No
No
not used
Synchronise
Transmit Status Word
Initiate RT Self-Test
RT Transmitter Shutdown
Override RT Transmitter Shutdown
Inhibit Terminal Flag
Override Inhibit Terminal Flag
Reset RT
No
Yes
mandatory
No
No
mandatory
No
Yes
mandatory
No
Yes
mandatory
No
Yes
mandatory
No
Yes
optional
No
Yes
optional
No
Yes
mandatory
No
TBD
not used
T/RBit
Mode
Code
hex (dec)
Function
1
00000 (0)
1
1
1
1
1
1
1
1
00001 (1)
00010 (2)
00011 (3)
00100 (4)
00101 (5)
00110 (6)
00111 (7)
01000 (8)
1
01001 (9)
to
01111 (15)
1
0
1
1
0
0
10000 (16)
10001 (17)
10010 (18)
10011 (19)
10100 (20)
10101 (21)
1
or
0
10110 (22)
to
11111 (31)
Reserved / illegal
Transmit Vector Word
Synchronise with Data Word
Transmit Last Command Word
Transmit RT BIT Word
Selected Transmitter Shutdown
Override Selected Transmitter Shutdown
Reserved / illegal
Yes
No
optional
Yes
Yes
mandatory
Yes
No
optional
Yes
No
optional
Yes
Yes
not used
Yes
Yes
not used
Yes
TBD
not used
Table 4.3-3: MIL-STD-1553B Mode Code Requirements for BepiColombo
BUS-104/[SD-1]/T
RT shall implement and respond to valid Mode Commands defined in Table 4.3-3 above as
required by [SD-1], para. 4.3.3.5.1.7.
BUS-301/Created/T,R
Use of Mode Code Commands marked as not used or optional (if not implemented in a RT) shall
be handled as illegal messages.
BUS-439/Created/T,R
The mode codes specified as optional shall be used if and only if they are demonstrated as
necessary for the BC-RT operations of an off-the-shelf RT unit that will not be functionally
modified for the BepiColombo project.
No use of these mode codes shall be claimed for equipment where no implementation of these
mode codes exist or where these mode codes are offered but are not identified as necessary for
the BC-RT operations.
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Specification
BepiColombo
Important note: in other words, if no RT equipment requires the use of the "Service Request" bit
and "Transmit Vector Word" mode code for asynchronous transfers, these MIL-STD-1553B
features will not be used on-board BepiColombo.
The above restriction is justified by the fact that for each of the highlighted optional mode codes
there exist other, more generic, MIL-STD-1553B mode codes or cyclic message transfers that
can answer the underlying need. For instance, "Transmit Vector Word" can be replaced with a
cyclic receive command that analyses a data word from the RT.
4.3.1.4.1
Synchronise
BUS-441/[SD-1]/T
Implementation of Mode Command "Synchronise" shall comply to [SD-1], para. 4.3.3.5.1.7.2.
4.3.1.4.2
Transmit Status Word
BUS-107/[SD-1]/T
Implementation of Mode Command "Transmit Status Word" shall comply to [SD-1], para.
4.3.3.5.1.7.3.
4.3.1.4.3
Initiate RT Self-Test
BUS-57/[SD-1]/T
Implementation of Mode Command "Initiate RT Self-Test" shall comply to [SD-1], para.
4.3.3.5.1.7.4.
4.3.1.4.4
RT Transmitter Shutdown
BUS-109/[SD-1]/T
Implementation of Mode Command "RT Transmitter Shutdown" shall comply to [SD-1], para.
4.3.3.5.1.7.5.
BUS-111/[SD-1]/T
The shutdown transmitter shall not generate any bus activity until the mode code is overridden
by either an "Override Transmitter Shutdown" mode code or a "Reset RT" mode code received
on the non-shutdown bus.
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Specification
4.3.1.4.5
BepiColombo
Override RT Transmitter Shutdown
BUS-113/[SD-1]/T
Implementation of Mode Command "Override RT Transmitter Shutdown" shall comply to [SD1], para. 4.3.3.5.1.7.6.
4.3.1.4.6
Inhibit Terminal Flag & Override Inhibit Terminal Flag (Optional)
BUS-828/[SD-1]/T
If "Inhibit Terminal Flag" and "Override Inhibit Terminal Flag" mode codes are necessary for
operation of an RT unit the implementation of these Mode Commands shall comply to [SD-1],
para. 4.3.3.5.1.7.7 resp. para. 4.3.3.5.1.7.8.
4.3.1.4.7
Reset Remote Terminal
BUS-115/[SD-1]/T
Implementation of Mode Command "Reset Remote Terminal" shall comply to [SD-1], para.
4.3.3.5.1.7.9.
BUS-116/Created/T
Receipt of the "Reset RT" mode code shall re-enable all shutdown transmitters. This reset shall
apply to the RT electronics only: the host electronics or computer shall be unaffected.
BUS-117/Created/T
The RT shall ensure that no disturbances of message exchanges occur after the "Reset RT"
because of residual RT data or flags.
If a remote terminal cannot respond normally while undergoing reset, the busy bit must be set in
the status word. The RT must be capable of receiving the next valid command.
4.3.1.4.8
Transmit Vector Word (optional)
BUS-968/Created/T,R
For BepiColombo project, service request of RT shall be handled using the Event Data
acquisition protocol as defined in section 5.6 of this document.
However, for heritage equipments Service request using the "Service Request Bit" and "Transmit
Vector Word" mode code for RT aperiodic operation may be granted upon request.
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Specification
BepiColombo
BUS-119/[SD-1]/T,R
If "Service Request Bit" and "Transmit Vector Word" mode code are necessary a RT unit, the RT
shall implement and respond to valid "Transmit Vector Word" mode code as required by [SD-1],
para. 4.3.3.5.1.7.11.
Figure 4.3-2 illustrates the use of the Transmit Vector Word command in association with the
Service Request Bit.
“0”
Figure 4.3-2: Transmit Vector Word Transfer
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Specification
BepiColombo
BUS-120/Created/T,R
The format of the Vector Word associated with an aperiodic message demand from the RT shall
be as specified in the Table 4.3-4.
Bit No.
Field Name
0
Format Flag
1 - 4 Reserved
5
T/R
Description
Shall be set to logic "0" to indicate "asynchronous message demand"
reserved: shall be set to logic "0"
Shall be set to a logic "1" to indicate that the requested message is a
transmit command. (Logic "0" indicates a receive command request.)
MSB
6
to
10
11
to
15
Subaddress
contain the subaddress of the required message
LSB
MSB
Word Count
contain the word count of the required message
LSB
Table 4.3-4: Vector Word Format for Aperiodic Message Demand from RT
BUS-122/Created/T,R
The format of the Vector Word associated with an aperiodic action demand from the RT shall be
as specified in the Table 4.3-5.
Should a RT use this Vector Word format, the "User defined" bit content and meaning shall be
specified by the RT supplier in the RT Unit Interface Control Document (ICD).
Bit No.
Field Name
0
Format Flag
1
to
Notification Flag
15
Description
Shall be set to logic "1" to indicate "asynchronous action demand"
MSB
User defined
LSB
Table 4.3-5: Vector Word Format for Aperiodic Action Demand from RT
BUS-451/Created/T,R
If there is only one possible message or action for an RT that asserts the "Service Request" bit,
then the BC shall know what action is required without any need for "Transmit Vector Word"
mode command. The RT Unit ICD submitted by the RT contractor shall specify that
message/action (TBC).
4.3.1.4.9
Synchronise with Data Word
BUS-52/[SD-1]/T
Implementation of Mode Command "Synchronise with Data Word" shall comply to [SD-1],
para. 4.3.3.5.1.7.12.
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Specification
BepiColombo
BUS-53/Created/T
The Data Word shall contain synchronisation information for the RT as defined in section 5.3.2
of this specification.
4.3.1.4.10 Transmit Last Command Word (optional)
BUS-135/[SD-1]/T,R
If "Transmit Last Command Word" mode code is necessary for the operations of an RT unit, RTs
shall implement and respond to valid "Transmit Last Command Word" mode code as required by
[SD-1], para. 4.3.3.5.1.7.13.
4.3.1.4.11 Transmit RT Built-In-Test (BIT) Word (optional)
BUS-137/[SD-1]/T,R
If "Transmit RT BIT Word" mode code is necessary for the operations of an RT unit, RTs shall
implement and respond to valid "Transmit BIT Word" mode code as required by [SD-1].
4.3.1.4.12 Prohibited Mode Codes
BUS-139/Created/T,R
The BC shall not transmit the mode codes specified as "Not used" in Table 4.3-3.
BUS-140/[SD-1]/T,R
The BC shall not transmit the reserved mode codes designated in [SD-1], nor any mode code not
defined in [SD-1].
BUS-141/Created/T,R
If a RT receives a prohibited mode command, the RT shall not alter the state of the RT unit.
4.3.2
Data Words
The Data Word Format shall be as defined by [SD-1] § 4.3.3.5.2. as required by [AD-1].
4.3.3
Status Words
BUS-145/[SD-1]/R
After the reception of any Mil-1553B-bus message (except broadcast message ), the RT shall
respond with a status word which shall be in accordance with [SD-1], para. 4.3.3.5.3.
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Specification
BepiColombo
BUS-444/Created/R
The Status Word Flags/Bits as specified in Table 4.3-6 shall be supported:
RT Status Bits
Bit
Time
Bit Setting
Status indication
Applicable
'0': absence of Error (default)
'1': presence of Error
indicates that message failed to
pass RT's validity tests
Yes
10
Set to '0' always
used to distinguish between
Command Word and Status Word
No
Service Request Bit
11
0': no service requested (default)
'1': service requested
indicates that RT requests
predefined action (see "Transmit
Vector Word" mode code)
Yes
Reserved
1214
15
Set to '000' always
0': no Broadcast Cmd received
(default)
'1': Broadcast Cmd received
indicates that preceding valid
command was a broadcast
command
Yes
Busy Bit
16
0': not busy (default)
'1': busy
indicates that the RT is unable to
receive or transmit in response to a
BC command
Yes
Subsystem Flag Bit
17
'0': absence of Error (default)
'1': presence of Error
indicates a subsystem/RT fault
Yes
Dynamic Control
Acceptance Bit
18
Set to '0' always
Function not implemented
No
Terminal Flag Bit
19
0': absence of a Fault Condition
(default)
'1': presence of a Fault Condition
indicates an RT fault
Yes
Message Error Bit
9
Instrumentation Bit
Broadcast Command
Received Bit
Table 4.3-6: Status Word Bit usage for BepiColombo
BUS-146/Created/T,R
The Status Word bits at bit times 10, 12, 13, 14, 17, 18 and 19 shall be set to a logical "0" by RT.
BUS-446/Created/R
The use of the Service Request bit, Subsystem Flag bit, the Busy bit, and the Terminal Flag bit
shall be defined by each RT in its User Manual or ICD.
4.3.3.1 Message Error Bit
BUS-148/[SD-1]/T,R
The Message Error Bit shall be implemented and used as defined in [SD-1].
BUS-149/Created/T
When a RT detects an error and sets this bit, none of the data received within the message shall
be used.
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BepiColombo
BUS-477/[SD-2]/T
If an RT that is designed with this option detects an illegal command and the proper number of
contiguous valid data words as specified by the illegal command word, it shall respond with a
status word only, setting the Message Error bit.
BUS-478/[SD-2]/T
Any data word(s) associated with a valid receive command that does not meet the word
validation checks (sync, Manchester, format, parity), or an error in the data word count, shall
cause the RT to set the Message Error bit in the status word to a logic one and suppress the
transmission of the status word.
BUS-479/[SD-2]/T
The suppression of the transmission of the Status Word by an RT because of a message error as
defined above shall generate a "no response time-out" on the BC side. This no response time-out
condition shall be recorded in the communication memory for later retrieval by the BC software
(TBC).
4.3.3.2 Instrumentation Bit
BUS-153/Created/T,R
The Instrumentation Bit shall always be set to logical "0". It shall not be used in conjunction
with a logical "1" in the MSB of the Command Word subaddress field to distinguish between a
Command Word and a Status Word.
4.3.3.3 Service Request Bit
BUS-156/[SD-1]/T
If the Service Request bit is necessary for the operations of an RT unit, it shall be implemented
and used as defined in [SD-1].
BUS-200/Created/T
The RT shall ensure that once the Service Request bit is set to logical "1", the Vector Word is
immediately available.
BUS-461/[SD-2]/T,R
The Service Request bit shall not be used to identify service requests for periodic message
transmissions.
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BepiColombo
BUS-450/Created/R
The use of the "Service Request" bit shall be submitted to the same restrictions as those specified
for the "Transmit Vector Word" mode code.
BUS-204/Created/T
The BC shall acquire data from the RT about service request by sending a "Transmit Vector
Word" command to the RT.
BUS-452/Created/R
The Vector Word shall define the action requested by the RT unit. The RT Unit ICD submitted by
the RT contractor shall specify vector word meaning.
BUS-207/Created/T,R
The RT shall maintain the current contents of the Vector Word until a subsequent and different
valid command has been received.
BUS-201/Created/T
The Service Request bit shall be reset to logical "0" when, and only when, the RT has received
the Transmit Vector Word mode command for the active service request and the Vector Word
has been transmitted.
BUS-205/Created/T,R
If the Service Request bit is still set to a logical "1" in a second or subsequent response to the
same service request, the Service Request bit shall be disregarded by the BC.
4.3.3.4 Broadcast Command Received Bit
BUS-158/[SD-1]/T,R
The Broadcast Command Received bit shall be implemented and used as defined in [SD-1].
4.3.3.5 Busy Bit
BUS-160/[SD-1]/T,R
If used by an RT, the Busy bit shall be implemented and used as defined in [SD-1], Notice II,
§30.5.3.
BUS-161/Created/T,R
The Busy bit by a Remote Terminal (RT) shall only be used in pre-defined conditions:
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BepiColombo
•
RT unit power-up, reset and initialisation: predictable, triggered from BC that shall
manage the delay before interrogating the RT.
•
RT unit self-test in progress: predictable, triggered from BC that shall manage the delay
before interrogating the RT.
•
RT self-test in progress: predictable, triggered from BC that shall manage the delay
before interrogating the RT.
•
The terminal goes busy for an unusual length of time or under unusual conditions: it
indicates a possible overload condition or a RT unit executing a non-interruptible
operation.
Busy times shall be provided by the RT unit contractor so as to determine the effects on data
latency on system level.
BUS-454/Created/T
The BC shall determine the busy condition:
•
immediately upon status response.
•
or, at the latest, at the end of the current minor frame (TBC).
4.3.3.6 Subsystem Flag Bit
BUS-164/[SD-1]/T
For equipment(/subsystem) providing the capability for self-test and connected to the bus as RT,
the Subsystem Flag bit shall be implemented and used as defined in [SD-1].
BUS-165/Created/R
Preferably RT equipment failures shall be reported as data words e.g. Event data accessible
from the relevant subaddress instead of using the Subsystem Flag bit (tbc).
4.3.3.7 Dynamic Bus Control Acceptance Bit
BUS-167/[SD-1]/T
Dynamic Bus Control function shall not be implemented on BepiColombo. Hence the Dynamic
Bus Control Acceptance Bit shall always be set to logical "0".
BUS-168/Created/T
The Bus Controller shall ignore a received Status Word that would contain the Dynamic Bus
Control Acceptance Bit in the Status Word set to logical "1".
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Specification
BepiColombo
4.3.3.8 Terminal Flag Bit
BUS-170/[SD-1]/T,R
For RT providing the capability for self-test, the Terminal Flag bit shall be implemented and
used as defined in [SD-1].
4.3.3.9 Status Word Reset/Update
BUS-739/[SD-1]/T
Status word bit reset shall be implemented as defined in [SD-1].
It is to be noted that:
•
Status is constructed on a message by message basis on receipt of each valid command
word. Remote terminals are required to store the status word between valid command
words so that it is available for interrogation using the transmit status word mode code.
•
It is recommended that the terminal flag bit and subsystem flag bit, having once been set,
should remain set until a reset remote terminal mode command is received or a power-up
initialization occurs.
•
The inhibit terminal flag mode code locally suppresses the terminal flag bit in the status
word so preventing failures of the RT from being reported in that way.
The above three facilities allow an orderly error handling and recovery approach to be
accomplished by the bus controller using the information associated with error analysis data
contained within the status word or other data associated with the RT (e.g. last command word
and BIT word).
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Specification
5
BepiColombo
Transfer Layer
BUS-180/Created/T,R
The BC shall only Transmit/receive messages to/from RTs which have the status "Active"
(powered, ready to be commanded...). This status shall be retrieved from a corresponding lookup table (Bus Configuration Table).
5.1
Message Formats and Timing
BUS-174/Created/T
The Bus Controller and Remote Terminals shall implement and use these message as specified in
[SD-1] para 4.3.3.6 and defined below to satisfy the system's requirements for data transfers
between BC and the RTs.
The message formats transmitted on the Mil-1553-Bus shall be in accordance with the structures
given in the sections below. No message formats, other than those defined below shall be used.
The exchange of data over the MIL-STD-1553B is based on message transmissions.
The MIL-STD-1553B standard defines 10 types of message transmission formats as recalled in
Figure 5.1-1 and Figure 5.1-2. All of these formats use the three (3) word types previously
defined.
Figure 5.1-1: Information Transfer Formats
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BepiColombo
Figure 5.1-2: Broadcast Information Transfer Formats
BUS-181/Created/T,R
The following Transfer Messages shall not be used onboard BepiColombo (TBC):
•
RT to RT Transfers as defined in [SD-1], para 4.3.3.6.3.
•
RT to RT Transfers (Broadcast) as defined in [SD-1], para 4.3.3.6.7.2.
•
Mode Command without Data Word (Broadcast) as defined in [SD-1], para 4.3.3.6.7.3.
5.1.1
BC to RT Data Message (Receive Message)
BUS-596/[SD-1]/T
The BC shall issue a Receive Command followed by the specified number of Data Words. The
Command and Data Words shall be transmitted in a contiguous fashion with no inter-word gaps.
The RT shall, after word / message validation, transmit a Status Word back to the BC.
See Figure 5.1-3.
This message sends data from the BC to the addressed RT.
BC to RT Transfer:
Receive
Data Word
Command
...
Data Word
**
Status
Word
#
Next
Command
Word
20μsec + N * 20μsec + 12μsec + 20μsec + 48μsec = 740μsec (for N=32)
**: response time, #: intermessage gap
Figure 5.1-3: BC to RT Data Message Format and Timing
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Specification
5.1.2
BepiColombo
RT to BC Data Message (Transmit Message)
BUS-725/[SD-1]/T
The BC shall issue a Transmit Command to the RT.
The RT shall, after transmit command validation, transmit a status word back to the BC,
followed by the specified number of data words. The status and data words shall be transmitted
in a contiguous fashion with no inter word gaps.
See Figure 5.1-4.
This message sends data from the addressed RT to the BC.
RT to BC Transfer:
Transmit
Command
.**.
Status
Word
Data Word
...
Data Word
#
Next
Command
Word
20μsec + 12μsec + N * 20μsec + 20μsec + 48μsec = 740μsec (for N=32)
**: response time, #: intermessage gap
Figure 5.1-4: RT to BC Data Message Format and Timing
5.1.3
Mode Command without Data Word Message
BUS-726/[SD-1]/T
The BC shall issue a mode command to the RT using a mode code specified in Table 4.3-3.
The RT shall, after command validation, transmit a status word. (No data words are sent)
See Figure 5.1-5.
This Message is sent from the BC to the addressed RT to control the RT.
Mode Command without Data Word:
Mode
Command
**
Status
Word
#
Next
Command
Word
20μsec + 12μsec + 20μsec + 48μsec = 100μsec
**: response time, #: intermessage gap
Figure 5.1-5: Mode Command without Data Word Message Format and Timing
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Specification
5.1.4
BepiColombo
Mode Command with Data Word from RT Message
BUS-728/[SD-1]/T
The BC shall issue a mode command to the RT using a mode code specified in Table 4.3-3. The
RT shall, after command validation, transmit a status word followed by one data word. The
status word and the data word shall be transmitted in a contiguous fashion with no inter word
gap.
See Figure 5.1-6.
This message sends a data word from the addressed RT to the BC, e.g. to provide housekeeping
information.
Mode Command with Data Word (Transmit):
Mode
Command
**
Status
Word
Data Word
#
Next
Command
Word
20μsec + 12μsec + 20μsec + 20μsec + 48μsec = 120μsec
**: response time, #: intermessage gap
Figure 5.1-6: Mode Command with Data Word from RT Message Format and Timing
5.1.5
Mode Command with Data Word from BC Message
BUS-745/[SD-1]/T
The BC shall issue a mode command to the RT using a mode code specified in Table 6.2-5,
followed by one data word. The command word and the data word shall be transmitted in a
contiguous fashion with no inter word gap.
The RT shall, after command and data word validation, transmit a status word back to the BC.
See Figure 5.1-7.
This Message is sent from the BC to the addressed RT to control the RT.
Mode Command with Data Word (Receive):
Mode
Data Word
Command
**
Status
Word
#
Next
Command
Word
20μsec + 20μsec + 12μsec + 20μsec + 48μsec = 120μsec
**: response time, #: intermessage gap
Figure 5.1-7: Mode Command with Data Word from BC Message Format and Timing
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Specification
5.1.6
BepiColombo
Broadcast BC to RT Command Message
BUS-746/[SD-1]/T
The BC shall issue a Receive Command Word with 11111 in the RT address field followed by the
specified number of Data Words.
The Command Word and Data Words shall be transmitted in a contiguous fashion with no gap.
The RTs with the broadcast option shall, after necessary validation, set the Broadcast Command
Received Bit in the Status Word as specified in BUS-158 and shall not transmit the status word.
See Figure 5.1-8.
This message sends data from the BC to the RTs (broadcast).
BC to RT(s) Transfer:
Receive
Data Word
Command
...
Data Word
#
Next
Command
Word
20μsec + N * 20μsec + 48μsec = 708μsec (for N=32)
**: response time, #: intermessage gap
Figure 5.1-8: Broadcast BC to RT(s) Data Message Format and Timing
5.1.7
Broadcast Mode Command with Data Word from BC Message
BUS-748/[SD-1]/T
The BC shall issue a Receive Command Word with 11111 in the RT address field and a Mode
Code specified in Table 4.3-3, followed by one Data Word.
The Command Word and Data Word shall be transmitted in a contiguous fashion with no gap.
The RT(s) with the broadcast options shall, after necessary validation, set the Broadcast
Command Received Bit in the Status Word as specified in BUS-158 and shall not transmit the
status word. See Figure 5.1-9.
This message sends data from the BC to the RTs (broadcast).
Broadcast Mode Command with Data Word (Receive):
Mode
Data Word
Command
#
Next
Command
Word
20μsec + 20μsec + 48μsec = 88μsec
**: response time, #: intermessage gap
Figure 5.1-9: Broadcast Mode Command with Data Word Message Format and Timing
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BepiColombo
5.1.8
Message Timing Requirements
Messages are separated by a period known as the intermessage gap, which is measured from
mid-bit zero crossing of the last bit of the preceding Message to the mid-bit zero crossing of the
next command word sync. In other words the intermessage gap consists of 0.5 µs of the parity
signal, the number of microseconds of dead-bus (zero voltage on the bus) between words, and
1.5 µs of the sync signal. Hence, the dead-bus time is the intermessage gap time minus 2µsec.
The timing requirements on word level are fully according to [SD-1] as required by [AD-1] and
given here as summary:
Data Bus Bit-Rate:
1 Mbps
Word Length:
20 bits (3 sync, 16 data bits, 1 parity bit) => ≅ 20µsec
BUS-184/[SD-1]/T
The Intermessage Gap to be provided by the Bus Controller (BC) shall comply to [SD-1], para
4.3.3.7.
Note: minimum Intermessage Gap of 4 μs.
BUS-185/Created/T
For BepiColombo the maximum Intermessage Gap shall be 48 µsec (TBC).
BUS-359/[SD-1]/T
The Response Time to be provided by the Bus Controller (BC) shall comply to [SD-1], para
4.3.3.7.
Note: Response Time between 4 to 12µsec.
BUS-183/[SD-1]/T
The Minimum No-Response Time-out shall comply to [SD-1], para 4.3.3.9.
Note: Minimum No-Response Time-out of 14 µs.
BUS-380/Created/T
The Bus Controller shall provide in addition the following programmable "No-Response TimeOut" values:
•
19 µs +/- 1 µs (TBC)
•
27 µs +/- 1 µs (TBC)
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Specification
5.1.9
BepiColombo
Message Validation
BUS-753/[SD-1]/T
Message Validation shall be fully according to [SD-1], para 4.4.3.
5.1.10
Max Busy Bit Set Times
BUS-191/Created/T,R
If a Remote Terminal (RT) is to delay further messages while executing a previous received
message, the RT shall set the Busy bit in the Status Word.
BUS-192/Created/T
The busy time shall be measured from the zero crossing of the parity bit of the last word of the
previous message to the zero crossing of the first command word sync which is accepted and
whose status response has the busy bit set to logical "0".
BUS-193/[SD-2]/T,R
The maximum RT busy time following the receipt of a valid "Reset RT" mode command shall be
5 ms.
BUS-455/[SD-2]/T,R
The maximum RT busy time for RT self-test shall be 100 ms.
BUS-194/[SD-2]/T,R
The maximum RT busy time following power application shall be 500 ms.
BUS-195/[SD-2]/T,R
The maximum RT busy time for all other allowed busy conditions shall be 50 µs.
BUS-460/Created/T,R
The BC shall notify RT busy conditions to the central software.
BUS-196/Created/T,R
When scheduling periodic message transfers, if the BC detects a Busy bit set in an RT Status
Word, it shall behave as follows:
•
no retry of the message shall be performed.
•
it shall continue with normal periodic message traffic of the next RT.
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Specification
5.1.11
BepiColombo
Data Wrap-Around
BUS-504/Created/T
RTs shall provide a receive subaddress to which one to N data words of any bit pattern can be
received. RTs shall provide a transmit subaddress from which a minimum of N data words can
be transmitted. N is equal to the maximum word count from the set of all messages defined for
the RT. A valid receive message to the data wrap-around receive subaddress followed by a valid
transmit command to the data wrap-around transmit subaddress, with the same word count and
without any intervening valid commands to that RT, shall cause the RT to respond with each
data word having the same bit pattern as the corresponding received data word. A data wraparound receive and transmit subaddress shall be implemented as defined in BUS-91 i.e at
subaddress 30.
BUS-503/Created/T
The BC shall implement the capability to perform wrap-around testing at RT subaddress 30, in
which data words sent to the RT with a receive command are send back to the BC with a
subsequent transmit command.
5.2
General Requirements
5.2.1
Communication with Non-Packet Terminals
BUS-45/Created/T
The Non-Packet Terminals within the BepiColombo project are (see also Figure 3.2-1):
MPO-1553B-Bus: MPO-PCDU, MPO-SADE, APME, DST-1, DST-2, KaT, BERM, IMU
MTM-1553B-Bus: MTM-PCDU, MTM-SADE, MPCU (MTM-CPS-I/O)
MMO-1553B-Bus: MMO
BUS-60/Created/T
For commanding (incl. data acquisition trigger commands) the BC shall issue Mil-1553B-bus
Receive Commands, followed by up to 32 data words in specific formats, to certain fixed
subaddress(es).
BUS-61/Created/T
For data acquisition, the BC shall issue Mil-1553B-bus Transmit Commands to fixed
subaddress(es) in response of which the RT shall transmit the requested data words (up to 32
data words).
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BUS-993/Created/T
The TC-Block length shall be limited to maximum 512 words (1024 octets).
BUS-994/Created/T
The TM-Block length shall be limited to maximum 512 words (1024 octets).
5.2.2
Communication with PUS-Packet Terminals and MMO
BUS-63/Created/T
The Packet Terminals within the BepiColombo project are (see also Figure 3.2-1):
MPO-1553B-Bus: STR-1, STR-2, STR-3 as PUS-Packet Terminals
MTM-1553B-Bus: MPCU (MEPS) as PUS-Packet Terminals
MMO-1553B-Bus: MMO (Packet Terminal, Non-PUS)
Data entities transferred to and from packet terminals are termed “blocks”.
TC-Blocks are transferred from the BC to RTs.
TM-Blocks are transferred from a RT to the BC.
BUS-65/Created/T
The BC and the Packet-RTs shall support the transfer of blocks of variable length, these blocks
are constraint to PUS Source Packets (except MMO).
BUS-69/Created/T
The TC-Blocks length shall be limited to maximum
•
MPO-1553B-Bus: 248 octets
•
MTM-1553B-Bus: 248 octets
•
MMO-1553B-Bus: 234 octets (TBC)
BUS-70/Created/T
The TC-Blocks shall be chopped into Messages of 32 data words for the transfer on the Mil1553B-bus. The messages making up a TC-Block Transfer shall not be interleaved by messages
of any other transfers.
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BepiColombo
BUS-71/Created/T
The TM-Blocks length shall be limited to
•
MPO-1553B-Bus: 4112 octets
•
MTM-1553B-Bus: 4112 octets
•
MMO-1553B-Bus: 4096 octets (TBC)
BUS-72/Created/T
The TM-Blocks shall be chopped into messages of 32 data words for the transfer on the 1553
Data Bus. The messages making up a TM-Block Transfer shall not be interleaved by messages of
any other transfers.
BUS-74/Created/T
In case of any failure during a block transfer, retransmission of complete blocks shall be
performed only. No retransmission of parts of a block is foreseen.
BUS-75/Created/T
Successful transfer of a block shall be acknowledged to the sending instance.
5.3
Frame Scheduling
BUS-348/Created/T,R
The Mil-Bus activities shall be structured into major frames, minor frames and message slots.
The scheduling of each BepiColombo MPO, MTM, MMO MIL-STD-1553B bus shall be
implemented in accordance with the following framing requirements and shown in Figure 5.3-1:
Note: The figure shows as an example only a sequence and allocation of TM/TC Transfers in the
Fixed and Disposable Section.
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BepiColombo
1 sec
Major Frame n-1
0
1
2
3
4
Major Frame n
5
6
7
0
1
2
3
4
Major Frame n+1
5
6
7
0
1
2
3
4
5
6
7
Minor Frames
125 msec
Minor Frame
Message Slots
0
1
2
3
4
.....
x
.....
Duration fixed but
individual for minor frame
Fixed Section
m
Possible bus
deadtime (margin)
Disposable Section
Synchronisation
IMU Functional Data
- STR event handling
- PCDU Nominal Commanding
STR Functional Data
- DST Nominal Commanding
APME Periodical Commanding
- STR Nominal Commanding
SADE Periodical Commanding
- SADE/APME Nominal Commanding & Data Acquisition
PCDU Trigger/Data Acquisition
- MORE Nominal Commanding
DST Trigger/Data Acquisition
- IMU Commanding & Data Acquisition (if required)
- BERM Nominal Commanding & Data Acquisition
MORE Trigger/Data Acquisition
- STR Data Acquisition (e.g. TM-Packets up to 4096 bytes)
BERM Trigger/Data Acquisition
Figure 5.3-1: Mil-Bus Scheduling (Major Frame / Minor Frame / Message Slot)
BUS-46/Created/T
The cyclic BepiColombo spacecraft Mil-1553B Data Bus Protocol shall have a deterministic,
periodic structure, which is synchronized with the central on-board time, implemented in the
OBC.
BUS-47/Created/T
The Mil-1553B-Protocol shall be based on a 1 second period called “Major Frame”.
BUS-48/Created/T
Each Major Frame shall be divided into 8 equidistant Time-Slots of 125 msec called “Minor
Frames”, each containing a number of MIL-STD-1553B messages. These messages shall occur
in a Minor Frame within a defined timing structure called "Message Slots".
BUS-49/Created/T
Each Minor Frame shall be organised in two sections.
•
A "Fixed Section" comprising a fixed sequence of Mil-Bus Transfers (messages) that
shall be executed at the beginning of a minor frame (i.e. periodical messages).
•
A "Disposable Section" comprising Mil-Bus Transfers to be added, triggered by
asynchronous events (e.g. commanding, error handling or transfer of periodic TM of
lower priority) to be executed after the fixed part has finished.
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BepiColombo
BUS-50/Created/T
The start of a minor frame shall be triggered by a OBC hardware real-time clock which also
controls the on-board software cycles to achieve high synchronisation between hardware and
software activities and to avoid any jitter and accumulation of timing errors.
This real-time clock and the start of the master frame shall be synchronized to the high precision
Pulse Per Second (PPS) signal which is derived from the OBT.
5.3.1
Frame Timing
BUS-351/Created/T
Each Minor Frame shall start with the Mode Command "Sync without Data Word" in the first
Message Slot (ref. BUS-540).
BUS-352/Created/T
The frame synchronisation shall be followed by the transmission of all the Fixed Section (i.e.
periodical) messages to be transferred in that Minor Frame.
BUS-537/Created/T,R
The minor frame Fixed Message transfer definition shall remain the same whichever active (i.e.,
non-OFF) operational mode the RT unit executes, i.e.:
•
On RT side, no constraint shall be imposed by the RT to manage different minor frame
scheduling regarding the periodic exchanges.
•
On BC side, the data utilisation discrimination vs. operational mode shall be performed
on a higher level of software than the MIL-STD-1553B protocol.
BUS-542/Created/T,R
Should an RT unit be OFF, no polling of this RT shall intervene during the relevant minor frame
with the following precisions:
•
The minor frame shall be without any transfers of messages if the minor frame is 100%
dedicated to this RT.
•
The synchronisation of the other RT's communication slots with respect to the minor
frame start/sync time shall remain unchanged in spite of the OFF state of this RT, i.e.,
the fact that a RT unit is OFF shall not affect the dynamics of the minor frame for the
other RTs sharing this minor frame with the OFF RT unit.
BUS-353/Created/T,R
After the Fixed Section messages, the Bus Controller (BC) shall use the remaining time to
transfer Disposable Section messages (i.e. aperiodic, error handling, TM data...).
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Specification
BepiColombo
BUS-539/Created/T
The BC shall queue the tasks to service RTs within a Message Slot, i.e. within a Message Slot the
RT servicing tasks shall be worked out one after the other and not at fixed time instants (TBC).
BUS-764/Created/T
Within a Message Slot activity (TC or TM block transfer) the bus line shall not be changed.
BUS-765/Created/T,A
If a TC or TM-Block transfer cannot be completed on one bus and is aborted, then the BC may
switch to the other bus (TBC). This means, that the transfer of a new sub-frame activity may be
on the other bus accordingly.
BUS-390/Created/T,A
The amount of time required to initiate each Major and Minor Frame shall be estimated. The
time required by the BC to set up for frame synchronization, during which it cannot send
messages, shall also be included.
BUS-524/Created/T,A
Flexible frame length with provision for overflow shall be avoided by design and construction.
Frame overruns shall be processed as an error which leads to the rejection of new aperiodic
message requests until frame overruns disappear (TBC).
BUS-538/Created/T,R
During a given minor frame, no other fixed message transfers than those dedicated to the
specified RTs shall take place (TBC).
BUS-756/Created/T
For the start of a TM Block Transfer the BC shall check the sizes of the available TM Blocks
returned by a RT.
BUS-766/Created/A
At the end of each sub frame a dead time period shall allow the RT to prepare for the following
sub frame. The dead time shall be not less than TBD msec (TBC).
BUS-767/Created/T,R
Each Packet-RT shall be polled for availability of TM Blocks and shall receive telecommands as
specified in the Polling Sequence Table (PST).
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Specification
BepiColombo
BUS-768/Created/T
To achieve operational flexibility, the PST shall be programmable (TBC).
This allows consideration of operating modes and configuration to avoid unnecessary FDIR
activities and to cover situations as
•
Set up of bus communication during power-on.
•
After resetting a subsystem (related to a certain RT), commanded by OBC or due to
subsystem watchdog reset.
•
Error recovery.
•
etc
BUS-770/Created/T,R
At least the following constraints applying to all programmed PSTs shall be taken into account
(TBC):
1. AOCS Control loop activities shall always run in sub-frame tbd.
2. One sub-frame per second will be defined to issue a single low level MIL-Bus command to any
RT (for trouble shooting purposes).
3. Each subaddress in each RT shall not be polled more than once per sub-frame.
4. further contraints are tbd.
5.3.2
Frame Synchronisation
"Syncronise with Data Word" Mode Command Procedure:
•
exclusively based on Mil-bus message exchange;
•
periodic "Synchronisation with Data Word" Broadcast Mode Command issued by the BC
at the start of each Minor Frame (no dedicated SCET transmitted).
BUS-540/Created/T
The BC shall issue in the first Minor Frame within each Major Frame the Broadcast Mode
Command "Synchronise", transmitted in the first message slot.
The RT can synchronize its activities to the BC activities by evaluating the minor frame count.
The overhead on the Mil-bus is negligible ( ~ 4 us/minor frame). RTs which do not need this
feature can simple ignore the mode command.
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Specification
BepiColombo
BUS-129/Created/T
The BC shall issue in all other Minor Frames the Broadcast Mode Command "Synchronize with
Data Word" to the RTs, transmitted in the first message slot to indicate the start of a Minor
Frame.
The Data Word provided with this command shall contain the minor frame number in which the
command is transmitted.
BUS-130/Created/T,R
The Data Word provided with the "Synchronize with Data Word" Broadcast Mode Command
shall comply to the following format:
Bit times 1 to 3: sync
Bit times 4 to 16: reserved, always set to logical "0"
Bit times 17 to 19:
Bit
time
17
Bit
time
18
Bit
time
19
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Minor Frame #0
Minor Frame #1
Minor Frame #2
Minor Frame #3
Minor Frame #4
Minor Frame #5
Minor Frame #6
Minor Frame #7
Bit time 20: Parity
BUS-131/Created/T
The RT shall synchronize its activities to the BC activities by evaluating the minor frame count.
BUS-783/Created/T
RTs which do not need "Synchronize with Data Word" Mode Command Procedure (Broadcast)
shall ignore this mode command.
5.3.3
Frame Utilisation
BUS-553/Created/T,A
The MPO-1553B-Bus framing and phasing shall respect the dynamic requirements as expressed
in Table 5.3-1 (TBC):
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Specification
BepiColombo
MPO
RT unit
[redund.]
IMU-A [hot]
IMU-B [cold]
Minor
Frame
section
Service
Rate
Fixed
8 Hz
Disposable
1 Hz
STR-1 [hot]
Fixed
8 Hz
Disposable
1Hz
Disposable
1Hz
Disposable
1Hz
STR-2 [hot]
Fixed
8 Hz
Disposable
1Hz
Disposable
1Hz
Disposable
1Hz
STR-3 [hot]
Fixed
8 Hz
Disposable tbd Hz
Disposable tbd Hz
Disposable tbd Hz
APME-A [hot]
Fixed
2 Hz
APME-B [cold] Disposable 1 Hz tbc
SADE-A [hot]
SADE-B [cold]
PCDU-A [hot]
PCDU-B [cold]
Fixed
2 Hz
Disposable 1 Hz tbc
Fixed
DST-1 [hot]
0,25Hz
to 2Hz
Disposable 2 Hz tbc
Fixed
1 Hz
DST-2 [hot]
Disposable 2 Hz tbc
Fixed
1 Hz
KaT (MORE)
Disposable 2 Hz tbc
Fixed
1 Hz
BERM
Disposable 2 Hz tbc
Fixed
1 Hz
Disposable 2 Hz tbc
Description
Constraints / Comments
Functional Data
1 to 4 TBC subsequent data sets
(i.e. 32Hz acquisition rate)
Nominal commanding / data as required
acquisition (HK, Diagnostic)
Functional Data
TM Source Packets
Event handling
as required
Nominal commanding
TC Source Packets
Data acquisition
TM Source Packets
Functional Data
TM Source Packets
Event handling
as required
Nominal commanding
TC Source Packets
Data acquisition
TM Source Packets
Functional Data
TM Source Packets
Event handling
as required
Nominal commanding
TC Source Packets
Data acquisition
TM Source Packets
Periodical Commanding
Nominal commanding / data as required
acquisition (HK, Diagnostic)
Periodical Commanding
Nominal commanding / data as required
acquisition (HK, Diagnostic)
Trigger/Data acquisition
TM data shall be ready 350ms
(tbc) after receipt of Trigger Cmd
Nominal commanding
Trigger/Data acquisition
TM data shall be ready 350ms
(tbc) after receipt of Trigger Cmd
Nominal commanding
Trigger/Data acquisition
TM data shall be ready 350ms
(tbc) after receipt of Trigger Cmd
Nominal commanding
Trigger/Data acquisition
TM data shall be ready 350ms
(tbc) after receipt of Trigger Cmd
Nominal commanding
as required
Trigger/Data acquisition
TM data shall be ready 350ms
(tbc) after receipt of Trigger Cmd
Nominal commanding
Table 5.3-1: MPO Framing/Phasing Requirements (TBC)
BUS-620/Created/T,A
The MTM-1553B-bus framing and phasing shall respect the dynamic requirements as expressed
in Table 5.3-2:
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Specification
BepiColombo
MTM
RT unit
[redund.]
MPCU_MEPSA
[hot]
MPCU_MEPSB
[cold]
MPCU-CPS-A
[hot]
MPCU-CPS-B
[cold]
SADE-A [hot]
SADE-B [cold]
PCDU-A [hot]
PCDU-B [cold]
Minor
Frame
section
Service
Rate
Fixed
Description
1 Hz tbc Functional Data
Constraints / Comments
TM Source Packets
Disposable
Disposable
1Hz
1Hz
Event handling
Nominal commanding
as required
TC Source packets
Disposable
Fixed
1Hz
8 Hz
Data acquisition
Commanding
TM Source packets
Thruster flow control valves,
Latch Valves
Valve Status, Pressure
Transducer, Thruster
Temperature
Disposable 8 Hz tbc Data acquisition
Fixed
2 Hz
Periodical Commanding
Disposable 1 Hz tbc Data acquisition (HK,
Diagnostic)
Fixed
0,25Hz Trigger/Data acquisition
to 2Hz
Disposable 0,5 Hz Nominal commanding
as required
TM data shall be ready 350ms
(tbc) after receipt of Trigger Cmd
as required
Table 5.3-2: MTM Framing/Phasing Requirements (TBC)
BUS-621/Created/T,A
The MMO-1553B-bus framing and phasing shall respect the dynamic requirements as expressed
in Table 5.3-3:
MMO
RT unit
[redund.]
Minor
Frame
section
MMO
N/A
Service
Rate
Description
Constraints / Comments
1 Hz tbc TM Data Blocks
1 Hz tbc TC Data Blocks
N/A
Event handling
Table 5.3-3: MMO Framing/Phasing Requirements (TBC)
5.3.4
BC Message Sequence Control
The transfer of data is subdivided into periodic messages and aperiodic messages (typically
event-driven).
A major cycle (or frame) is defined so that all periodic messages are transferred at least once.
Minor frames are then established to meet the requirements of the higher update rate messages.
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Specification
BepiColombo
BUS-217/Created/T,R
The Bus Controller (BC) shall provide the host processor software with a service that allows to
specify linear sequences of messages that are to be exchanged over the MIL-STD-1553B bus.
BUS-225/Created/T
It shall be possible to initiate BC message sequences as follows:
•
upon Real-Time Clock (RTC) interrupt: 1 Hz or 1s Major Frame.
•
upon Real-Time Clock (RTC) interrupt: 8 Hz or 125 ms Minor Frame.
•
upon host processor software command.
BUS-226/Created/T
It shall be possible to perform the following operations upon host processor software
commands:
•
to suspend the execution of a sequence #i.
•
to insert and execute a new sequence #j.
•
to resume and complete the execution of the sequence #i.
BUS-212/Created/R
The Bus Controller (BC) shall provide a Communication Memory (EDAC-protected volatile
memory area), dedicated to the MIL-STD-1553B exchanges between the BC software and the
Remote Terminals (RTs).
BUS-213/Created/R
The sizing of the Communication Memory shall provide 50% margin (TBC).
5.3.5
Bus Loading
BUS-357/Created/T,A
MPO minor frame loading shall be less than tbd % for worst case.
BUS-554/Created/T,A
MTM minor frame loading shall be less than tbd % for worst case.
BUS-594/Created/T,A
MMO minor frame loading shall be less than tbd % for worst case.
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Specification
5.4
BepiColombo
Time Synchronisation
The following procedures shall apply on board BepiColombo for the purpose of RT time
reference synchronisation for all PUS Packet Terminal users and all other users requiring the
time reference:
"Syncronise" Mode Command Procedure:
•
exclusively based on Mil-bus message exchange;
•
distribution of SCET using Receive Command (BC to RT Transfer) followed by a
"Synchronise" Mode Command issued by the BC.
PPS-based Synchronisation Procedure:
•
based on Mil-Bus message exchange and provision of discrete syncronisation pulse
(PPS) to RT;
•
distribution of SCET using Receive Command (BC to RT Transfer) followed by discrete
syncronisation pulse issued by the BC to the RT.
BUS-781/Created/R
The baseline allocation of the defined Synchronisation Procedures to the Remote Terminals
shall be as given in Table 5.4-1:
Mil-Bus
RT Unit
Syncronise PPS-based
Mode Cmd
Sync.
Proc.
Proc.
Sync. with
DW Mode
Cmd Proc.
MPO-1553-Bus STR-1 to -3
IMU
BERM
MPO-PCDU
MPO-SADE
APME
DST-1 to -2
KaT (MORE)
MTM-1553-Bus MPCU-MEPS
MPCU-CPS
MTM-PCDU
MTM-SADE
N
TBD
TBD
N
N
N
N
N
Y
N
N
N
Y
N
N
N
N
N
N
N
N
N
N
N
N
Y
Y
Y
Y
Y
Y
Y
N
Y
Y
Y
MMO-1553Bus
TBD
N
TBD
MMO
Table 5.4-1: RT Synchronisation Procedure Allocation
BUS-370/Created/T
The BC shall provide system time information (SCET) via the Mil-1553B-busses.
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BepiColombo
BUS-371/Created/T
The SCET distribution over MIL-STD-1553B bus shall have the format as specified in Table
5.4-2 with the time value given in second according to the following equation, consistent with the
CCSDS Unsegmented Time Code (CUC) format:
SCET = C1*2563 + C2*2562 + C3*256 + C4 + F1*256-1 + F2*256-2
Bit Position:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
MSB
Data Words:
17
18
19
20
LSB
Sync
Reserved = 0000 0000 bin
P-Field = 0010 1110 bin
P
Sync
Coarse Time C1 (MSB)
Coarse Time C2
P
Sync
Coarse Time C3
Coarse Time C4
P
Sync
Fine Time F1
Fine Time F2 (LSB)
P
Table 5.4-2: MIL-STD-1553B SCET Distribution Format
BUS-795/Created/T
The time value contained in the time message shall be the time at the beginning of the next
frame. Reference is the beginning of the Mode Command "Synchronise" of Minor Frame 0.
BUS-124/Created/A
The relative accurracy of the time information shall be max. TBD microseconds with respect to
the system time of the BC (OBC).
BUS-126/Created/T
The time information shall be a message sent to subaddress 27R (TBC).
BUS-810/Created/T
The BC shall send the information in Minor Frame TBD (Message slot TBD).
5.4.1
Synchronise Mode Command Procedure
BUS-443/Created/T
For time synchronisation using "Syncronise" Mode Command Procedure, the BC shall distribute
to the RT, at the specified subaddress, the SCET valid at the next "Syncronise" Mode Command
sent over the bus.
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Specification
BepiColombo
The SCET shall be sent during the preceding minor frame allocated to this RT to give sufficient
time to the RT for preparing the next re-synchronisation.
BUS-133/Created/T
RTs to be synchronised to SCET using "Syncronise" Mode Command Procedure shall:
•
receive the SCET through the specified subaddress with the SCET data word format
according to BUS-371,
•
re-synchronise the RT unit local time with the pre-loaded SCET upon reception of the
"Synchronise" Mode Command (defined by BUS-441).
BUS-973/Created/T
In case no SCET was sent in any of the Minor Frames during the last Major Frame, no
resynchronisation shall be performed.
5.4.2
PPS-based Synchronisation Procedure
BUS-786/Created/T
For RTs synchronised using "PPS-based Syncronisation Procedure", the BC shall distribute to
the specified subaddress of the RT the SCET, valid at the next discrete Pulse Per Second (PPS)
signal sent to the RT.
The SCET shall be sent during a preceeding minor frame to this RT to give sufficient time to the
RT for preparing the next re-synchronisation.
BUS-787/Created/T
RTs to be synchronised to SCET using PPS-based Syncronisation Procedure shall:
•
receive the SCET through the specified subaddress with the SCET data word format
according to BUS-371,
•
re-synchronise the RT unit local time with the pre-loaded SCET upon reception of the
subsequent discrete Pulse Per Second (PPS) pulse (rising edge).
5.5
Block Transfer Protocol
5.5.1
General
BUS-790/Created/R
A Block is defined as a sequence of data words to be transferred over the Mil-1553B-Bus.
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BepiColombo
BUS-796/Created/T
The Block Transfer Protocol shall be based on the exchange of two Transfer Descriptor Words
between BC and RT for block data request (at start of block transfer) and confirmation of block
received (at the end of block transfer).
Dedicated sub-addresses shall be used as defined in BUS-91.
BUS-794/Created/T
The data block itself shall be transferred, initiated and terminated by Transfer Descriptor
exchange, as a sequence of Mil-1553B-Bus messages via dedicated RT subaddresses as defined
in BUS-91.
BUS-791/Created/T,A
A Block Transfer shall not be interleaved by any other data transfer (TBC).
BUS-793/Created/T
The block of data to be transferred shall be chopped into sections (i.e. Mil-1553B-Bus
messages). All sections shall comprise 32 data words except the last one which may have less
than 32 words depending on the Block length.
If Block length is an odd number of bytes, the last word shall contain the last byte of the initial
data in its most significant bits, the least significant bits shall be set to “0”.
BUS-802/Created/T
The first Transfer Descriptor word "Transfer Size" shall define the length of the compete block
to be transferred expressed in number of 16-bit words. The format shall be as given in Figure
5.5-1.
Unused bits (00 to 03) shall be set to logic "0".
BUS-803/Created/T
The second Transfer Descriptor word "Transfer Control" shall hold the Transfer type, the
Transfer status, the Transfer Flow Control bits and the Block Count. The format shall be as
given in Figure 5.5-1.
Unused bits shall be set to logic "0".
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Specification
BepiColombo
Number of 16-bit words of block
Bit position
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15
Transfer
Type
Bit position
Transfer Size
Transfer
Status
Transfer
Control
Block Count
Transfer Control
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15
Transfer size:
1..0809 hex
0
Number of 16-bit words
No transfer
Transfer type:
00 bin
01 bin
= use only subaddress 1
= increment subaddress 1 to 16
Transfer status:
00 bin
01 bin
10 bin
11 bin
= no error
= transmission error
= protocol error
= reserved
Transfer Flow
control:
00 bin
01 bin
10 bin
11 bin
= no request
= request
= transmission finished
= protocol reset
Block Count:
1..0F hex
To be incremented by 1 for each block
request (starting value 00 hex),
roll over after reaching 0F hex
Figure 5.5-1: Block Transfer Descriptor Words
BUS-805/Created/T,R
The protocol supports two different transfer types which shall be fixed for a RT:
•
case 1: the TM or TC data are written/read to/from subaddress 1 (limited to 4112 bytes)
•
case 2: the sub-address is incremented by one after the transfer of a Mil-bus message (32
words) from one to 16 (total length of data block limited to 1024 bytes).
BUS-799/Created/R
Data integrity of received data on block level (e.g. contiguous message sequence counter) is not
verified by this Mil-bus protocol, since failures during data transfer are monitored on message
level.
BUS-801/Created/R
No retry of block transfer, neither in part or complete, is foreseen on Mil-bus protocol level,
except TM block retention on RT side on BC request (TBC).
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Specification
5.5.2
BepiColombo
BC to RT Block Transfer (Command Distribution)
BUS-806/Created/T,R
The BC shall be responsible for limiting the TC block length to the maximum number of words.
BUS-807/Created/T
The BC shall queue the TC blocks if there are more TC blocks with the same destination waiting
for transmission.
BUS-808/Created/T
The BC to RT Block Transfer shall be implemented according to the procedure (steps) defined
below and shown in Figure 5.5-2 (Simplified Flow Control Diagram).
BC
RT
Start of Transfer
Start of Transfer
BC sends TC data to RT buffer(s) at SA 1(-16)
BC sends TC Transfer Descriptor to RT at SA 29
(TC Transfer Request)
BC waits for TC Transfer Confirmation (SA 29)
RT reads and checks Transfer Descriptor at SA 29
and checks block count against previous one.
New count Id?
No
Yes
RT reads TC data at SA 1(-16) acc to transfer size
RT stores updated Transfer Descriptor at SA 29
(TC Transfer Confirmation)
BC reads and evaluates Transfer Descriptors
of TC Transfer Confirmation
Time-out
End of Transfer
End of Transfer
Figure 5.5-2: BC to RT Block Transfer (simplified)
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Specification
BepiColombo
BUS-897/Created/T
Step 1:
The BC shall send the command data block (TC-Packet) to the RT by issuing a number of
Receive Command Messages according to the number of words to be transmitted and the
Transfer Type (preselected for the RT) to the relevant TC Data Buffer(s) beginning at sub
address 1.
BUS-898/Created/T
Step 2:
The BC shall prepare the TC Data Transfer Request by sending the Transfer Descriptor Words
to RT subaddress 29.
First the Transfer Size Word with the number of 16 bit words of the block, followed by the
Transfer Control Word providing Transfer Type (predefined for RT), Transfer status=00bin,
Transfer Flow control = 01bin and Block Count incremented by one.
BUS-899/Created/T
Step 3:
The RT shall read the TC Data Transfer Request on subaddress 29 (interrupt or polling).
BUS-900/Created/T
Step 4:
The RT shall check if the TC Data Transfer Request is a new one by comparing the received
Block Count against the previous one.
BUS-901/Created/T
Step 5:
If it is a new TC Data Transfer Request, the RT shall read the block data from the Mil-1553Bbus buffers (TC Data Buffers) into memory.
BUS-902/Created/T
Step 6:
The RT shall update the TC Data Transfer Confirmation providing the corresponding Transfer
Descriptor Words in sub-address 29:
•
Transfer Size Word: number of 16 bit words received
•
Transfer Control Word: Transfer type (predefined), Transfer Status=00bin, Transfer
Flow control = 10 bin, Block Count = counter of block received.
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BUS-903/Created/T
Step 7:
The BC shall poll the TC Data Transfer Confirmation Descriptor Words from sub-address 29
and evaluate the transfer flow.
5.5.3
RT to BC Block Transfer (Data Acquisition)
BUS-830/Created/T
The RT to BC Block Transfer shall be implemented according to the procedure defined below
and shown in Figure 5.5-3 (Simplified Flow Control Diagram).
BC
RT
Start of Transfer
Start of Transfer
RT stores TM data to TM buffer(s) at SA 1(-16)
RT stores TM Transfer Descriptor at SA 28
(TM Transfer Request)
RT waits for TM transfer Confirmation (SA 28)
RT reads and checks Transfer Descriptor at SA 29
and checks block count against previous one.
Valid, but old
count Id
New count Id?
Invalid request
or protocol reset
New valid count Id and request
BC reads TM data at SA 1(-16) acc to transfer
type and transfer size
RT sends Transfer Descriptor at SA 28
(TM Transfer Confirmation)
RT evaluates Transfer Descriptor
of TM Transfer Confirmation
End of Transfer
End of Transfer
Time-out
Figure 5.5-3: RT to BC Block Transfer (simplified)
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BUS-904/Created/T
Step 1:
The RT shall store the data block (TM-Packet) into the TM Data buffer(s) at dedicated
subaddress(es) as defined in BUS-91, beginning at SA 1.
BUS-905/Created/T
Step 2:
The RT shall prepare the TM Data Transfer Request by storing the corresponding Transfer
Descriptor Words in subaddress 28:
•
First the Transfer Size Word with the number of 16 bit words of the block
•
then the Transfer Control Word defining Transfer type (predefined for RT), Transfer
status = 00bin, Transfer Flow control = 01bin and Block Count incremented by one.
BUS-911/Created/T
Step 3:
The RT shall wait for the TM Data Transfer Confirmation from the BC (Receive Command
Message providing Transfer Descriptors). If no transfer confirmation is received within TBD ms
(time-out), the RT shall abort the block transfer and generate an exception report (TBC).
BUS-906/Created/T
Step 4:
The BC shall poll the TM Data Transfer Request at subaddress 28 by issuing a related Transmit
command (2 words) to acquire the Transfer Descriptor Words.
BUS-907/Created/T
Step 5:
The BC shall check if the TM Data Transfer Request is a new one. This shall be done by
checking the acquired Transfer Control Word for Transfer Flow control == 01bin and
comparing the received Block Count against the value of the previous block received.
BUS-908/Created/T
Step 6:
If it is a new and valid request, the BC shall read the data block (TM-Packet) from the RT by
issuing a number of Transmit Command Messages according to the number of words to be
transmitted (defined in Transfer Size Word) and the Transfer Type (Transmit Control Word)
from the relevant TM Data Buffer(s) beginning at sub address 1.
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BUS-909/Created/T
Step 7:
The BC shall evaluate the status words of the Transmit Command Messages and send the
updated Transfer Descriptor Words to the TM Data Transfer Confirmation RT subaddress 28.
The Transfer Descriptor words shall provide
•
Transfer Size Word: number of 16 bit words received
•
Transfer Control Word: Transfer type (predefined), Transfer Status=00bin, Transfer
Flow control = 10 bin, Block Count = counter of block received.
BUS-910/Created/T
Step 8:
The RT shall evaluate the transfer flow using the TM Data Transfer Confirmation Words at subaddress 29.
5.6
Event Data Acquisition
BUS-896/Created/T
Event Data/Messages shall consist of small messages sent by the RT for reporting an event
which requests an immediate reaction from the OBC equipment management or FDIR.
BUS-935/Created/T
Event Messages shall fit into one Mil-1553B-Bus message (max. 32 words). The individual
format of the Event Message shall be defined in the specific equipment ICD.
BUS-922/Created/T
The Event Message Handling Protocol shall be based on the exchange of two Event Transfer
Descriptor Words between BC and RT for Event Data Request (start of transfer) and
confirmation of Event Message received (end of transfer).
Dedicated sub-addresses shall be used as defined in BUS-91 (Event Data Transfer Request on
SA 26 T, Event Data Transfer Confirmation on SA 26 R).
BUS-923/Created/T
The first Event Transfer Descriptor word "Transfer Size" shall define the Event Message length
to be transferred expressed in number of 16-bit words. The format shall be as given in Figure
5.5-1 with the following deviations:
•
Bits 10 to 15 shall define the number of 16bit words in the range 001 to 020 hex.
•
Bits 00 to 09 are reserved and shall be set to logic "0".
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BUS-924/Created/T
The second Event Transfer Descriptor word "Transfer Control" shall hold the Transfer type, the
Transfer status, the Transfer Flow Control bits and the Block Count. The format shall be as
given in Figure 5.5-1 with the following deviations:
•
Transfer type always set to 00bin (only SA 25 for Event data)
•
Block Count shall be used as Event Message counter following the same priciple rules.
•
Bits 02, 03, 08 to 11 are reserved and shall be set to logic "0"..
BUS-914/Created/T
The followingEvent Data Transfer Protocol shall apply to handle events:
BUS-915/Created/T
Step 1:
The RT shall store the Event Message data into the Event Message Data buffer at dedicated
subaddress 25.
BUS-916/Created/T
Step 2:
The RT shall prepare the Event Data Transfer Request by storing the corresponding Event
Transfer Descriptor Words in subaddress 26:
•
First the Transfer Size Word with the number of 16 bit words
•
then the Transfer Control Word defining Transfer type (always 00bin), Transfer status =
00bin, Transfer Flow control = 01bin and Event Message Count incremented by one.
BUS-917/Created/T
Step 3:
The RT shall wait for the Event Data Transfer Confirmation from the BC (Receive Command
Message providing Transfer Descriptors).
If no transfer confirmation is received within TBD ms (time-out), the RT shall abort the block
transfer and generate an exception report (TBC).
BUS-918/Created/T
Step 4:
The BC shall poll the Event Data Transfer Request at subaddress 26 as defined in the PST for a
new request by issuing a related Transmit command (2 words) to acquire the Event Transfer
Descriptor Words.
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BUS-919/Created/T
Step 5:
The BC shall check if the Event Data Transfer Request is a new one. This shall be done by
checking the acquired Event Transfer Control Word for Transfer Flow control == 01bin and
comparing the received Event Message Count against the value of the previous Event Message
received.
BUS-920/Created/T
Step 6:
If it is a new and valid request, the BC shall read the Event Message from the RT at SA 25 by
issuing a Transmit Command Messages with the length as defined in the request.
BUS-921/Created/T
Step 7:
The BC shall evaluate the status words of the Transmit Command Messages and send the
updated Event Transfer Descriptor Words to the Event Data Transfer Confirmation at RT
subaddress 26. The Transfer Descriptor words shall provide
•
Transfer Size Word: number of 16 bit words received
•
Transfer Control Word: Transfer Status=00bin, Transfer Flow control = 10 bin, Event
Message Count = counter of Event Message received.
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5.7
Commanding and Data Acquisition of Non-Packet Terminals
5.7.1
MPO-PCDU, MTM-PCDU, DST, MORE (tbc) and BERM (tbc)
BUS-833/Created/R
The following requirements shall be applicable for MPO-PCDU, MTM-PCDU, DST-1, DST-2,
MORE (tbc) and BERM (tbc).
BUS-841/Created/T
Nominal commanding shall be performed at the beginning of the fixed cycle with a frequency of
2 Hz to each of the relevant units using the Block Transfer Protocol (BC to RT Block transfer) as
specified in section 5.5 of this document.
BUS-929/Created/T
For nominal commanding, the Block Transfer Protocol (BC to RT Block transfer) as specified in
section 5.5 of this document shall apply.
BUS-842/Created/T
For nominal commanding a dedicated subaddress (SA 1 up to SA 16) shall be used.
BUS-895/Created/T
The maximum length of a nominal command data block shall not exceed 1 message (on 1
subaddress with up to 32 words (16 bit)).
BUS-843/Created/T
Nominally no commanding shall be foreseen between the TM Trigger Command and the
corresponding TM Data acquisition.
BUS-834/Created/T
The periodic, functional housekeeping data preparation of the RT shall be started by a dedicated
"TM Data Trigger Command" from BC to RT.
BUS-890/Created/T
The TM Data Trigger Command shall be a Receive Command (BC to RT Transfer) Message
comprising one Data Word.
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BUS-891/Created/T,R
The data word of the TM Data Trigger Command shall be used to identify the different trigger
command functions as defined in Table 5.7-1.
To be defined.
Table 5.7-1: TM Data Trigger Command Word
BUS-835/Created/T
The TM Data Trigger Command shall use a dedicated sub-address 23, common to all RTs.
BUS-893/Created/T
TM Data Trigger Commands shall be transfered at the beginning of the Minor Frame Fixed
Section to each of the relevant units.
BUS-836/Created/T
After the RT has received the TM Data Trigger Command and a delay time of 350ms (TBC), the
data shall be available for acquisition until the next TM Data Trigger Command is sent to the
RT.
BUS-894/Created/T
After the TM Acquisition delay time defined in BUS-836, the BC shall acquire the Telemetry
data from the RT in the Fixed Section of a Minor Frame.
BUS-930/Created/T
For Telemetry data acquisition, the Block Transfer Protocol (RT to BC Block transfer) as
specified in section 5.5 of this document shall apply.
BUS-837/Created/T
Predefined for each RT, a dedicated subaddress (SA 1) or a series of dedicated subaddresses (SA
1 up to SA 16) as defined in BUS-91 shall be used for data transmission.
The RT shall indicate it's Transfer type in the Transfer Descriptor Transfer Control Word
accordingly.
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BUS-838/Created/T
The maximum length of the Telemetry data shall be 16 messages (on 16 sub-addresses with up to
32 words each) or 512 words (16 bit).
BUS-839/Created/T
The data shall include a wraparound counter or flag allowing to determine the validity of the
acquired data; Additionally, for the applicable protocol, the validity is indicated by the update of
the ‘Block Count’ field within the Transfer Control word of the Transfer Descriptor.
BUS-840/Created/T
The frequency of the acquisition/triggering shall be selectable from 0,25 Hz to 2Hz.
BUS-844/Created/T,R
If required, diagnostic or aperiodic data shall be transmitted (RT to BC) on the same subaddress(es) as used for the periodic, functional data using the same transfer protocol.
BUS-845/Created/T,R
The transfer of diagnostic or aperiodic data shall be performed in the Minor Frame Disposable
Section following the nominal commanding.
BUS-855/Created/T,R
If required, Event data (message) shall be acquired from the RT by the BC in the Disposable
Section of a Minor Frame using the Event Message Handling Protocol as specified in section 5.6
of this document.
5.7.2
MPO-SADE, MTM-SADE and APME (HGA & MGA)
BUS-847/Created/R
For MPO-SADE, MTM-SADE and APME (HGA and MGA) the following requirements shall
apply:
BUS-851/Created/T
Nominal commanding (e.g. mode commands or update of parameters) shall be performed at the
beginning of the Minor Frame Disposable Section at a frequency of 1Hz (tbc).
BUS-925/Created/T
For nominal commanding, the Block Transfer Protocol (BC to RT Block transfer) as specified in
section 5.5 of this document shall apply.
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BUS-926/Created/T
For nominal commanding a dedicated subaddress (SA 1 up to SA 16) shall be used.
BUS-848/Created/T
Periodical commanding (e.g. position and rate) shall be performed in the Fixed Section of a
Minor Frame at a frequency of 2Hz (tbc).
BUS-850/Created/T
For periodical commanding, the Block Transfer Protocol (BC to RT Block transfer) as specified
in section 5.5 of this document shall apply.
BUS-849/Created/T
For periodical commanding a dedicated subaddress (SA 1 up to SA 16) shall be used.
BUS-982/Created/T,R
Nominal commanding and periodical commanding shall use different subaddresses (tbc).
BUS-852/Created/T,R
If required, diagnostic or aperiodic data shall be acquired by the BC in the Disposable Section
of the Minor Frame following the nominal commanding Minor Frame.
BUS-853/Created/T,R
For transfer of diagnostic or aperiodic data from the RT to the BC, the Block Transfer Protocol
(RT to BC Block transfer) as specified in section 5.5 of this document shall apply.
BUS-927/Created/T,R
For acquisition of diagnostic or aperiodic data a dedicated subaddress (SA 1 up to SA 16) shall
be used.
Diagnostic and aperiodic data shall use the same subaddress(es).
BUS-856/Created/T,R
If required, Event data shall be acquired from the RT by the BC in the Disposable Section of a
Minor Frame using the Event Message Handling Protocol as specified in section 5.6 of this
document.
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5.7.3
BepiColombo
IMU
BUS-932/Created/R
For IMU the following requirements shall apply:
BUS-854/Created/T
IMU Functional Data shall be aquired in the Fixed Section of the Minor Frame with a frequency
of 8Hz.
At this rate, 1 up to 4 (TBC) subsequent sets of functional data shall be transfered.
BUS-931/Created/T
For transfer of IMU Functional Data to the BC, the Block Transfer Protocol (RT to BC Block
transfer) as specified in section 5.5 of this document shall apply.
BUS-928/Created/T
A dedicated subaddress (SA 1) or a series of dedicated subaddresses (SA 1 up to SA 16) as
defined in BUS-91 shall be used for data transmission.
The RT shall indicate it's Transfer type in the Transfer Descriptor Transfer Control Word
accordingly.
BUS-976/Created/T
IMU commanding shall be performed at the beginning of the Minor Frame Disposable Section
at a frequency of 8Hz (tbc).
BUS-977/Created/T
For IMU commanding, the Block Transfer Protocol (BC to RT Block transfer) as specified in
section 5.5 of this document shall apply.
BUS-978/Created/T
For IMU commanding a dedicated subaddress (SA 1 up to SA 16) shall be used.
BUS-979/Created/T,R
If required, diagnostic data shall be acquired by the BC in the Disposable Section of the Minor
Frame following the IMU commanding Minor Frame.
BUS-980/Created/T,R
For transfer of diagnostic data from the RT to the BC, the Block Transfer Protocol (RT to BC
Block transfer) as specified in section 5.5 of this document shall apply.
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BUS-981/Created/T,R
For acquisition of IMU diagnostic data a dedicated subaddress (SA 1 up to SA 16) shall be used.
BUS-983/Created/T,R
IMU functional data and diagnostic data shall use different subaddresses (tbc).
BUS-975/Created/T
If required, Event data shall be acquired from the RT by the BC in the Disposable Section of a
Minor Frame using the Event Message Handling Protocol as specified in section 5.6 of this
document.
5.7.4
MPCU-CPS-I/O (TBC)
BUS-985/Created/R
For MPCU-CPS (dedicated RT for CPS-I/O function inside MPCU) the following requirements
shall apply:
BUS-986/Created/T
MPCU-CPS commanding shall be performed in the Fixed Section of the Minor Frame with a
frequency of 8Hz.
BUS-987/Created/T
For MPCU-CPS commanding, the Block Transfer Protocol (BC to RT Block transfer) as
specified in section 5.5 of this document shall apply.
BUS-988/Created/T
For MPCU-CPS commanding a dedicated subaddress (SA 1 up to SA 16) shall be used.
BUS-989/Created/T
MPCU-CPS Functional Data shall be aquired in the Disposable Section of the Minor Frame
with a frequency of 8Hz (TBC).
BUS-990/Created/T
For transfer of MPCU-CPS Functional Data to the BC, the Block Transfer Protocol (RT to BC
Block transfer) as specified in section 5.5 of this document shall apply.
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BUS-991/Created/T
A dedicated subaddress (SA 1) or a series of dedicated subaddresses (SA 1 up to SA 16) as
defined in BUS-91 shall be used for data RT data acquisition.
The RT shall indicate it's Transfer type in the Transfer Descriptor Transfer Control Word
accordingly.
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5.8
BepiColombo
Commanding and Data Acquisition of PUS-Packet Terminals
BUS-857/Created/R
For PUS-Terminals STR-1, STR-2, STR-3, MPCU-MEPS (dedicated RT to MTM Electric
Propulsion Subsystem) connected to the Mil-1553B-bus the following requirements shall apply:
BUS-797/Created/T
Nominal commanding, i.e. transfer of TC Source Packets, shall be performed in the Disposable
Section of the Minor Frame with a frequency of 1Hz (tbc).
BUS-912/Created/T
For transmission of TC Source Packets from the BC to the RT, the Block Transfer Protocol (BC
to RT Block transfer) as specified in section 5.5 of this document shall apply.
BUS-858/Created/T
The TC-Block (TC Source Packet) shall be written to RT subaddress 1 only.
The RT shall indicate this Transfer type in the Transfer Descriptor Transfer Control Word
accordingly.
BUS-859/Created/T
Nominal TM Data Acquisition (Housekeeping), i.e. transfer of TM Source Packets, shall be
performed in the Disposable Section of the Minor Frame with a frequency of 1Hz (tbc).
BUS-863/Created/T
STR functional data, i.e. TM Source Packets, shall be acquired by the BC in the Fixed Section of
the Minor Frame with a frequency of 8Hz.
BUS-934/Created/T
MPCU-MEPS functional data, i.e. TM Source Packets, shall be acquired by the BC in the Fixed
Section of the Minor Frame with a frequency of 1Hz (tbc).
BUS-933/Created/T
For transmission of TM Source Packets from the RT to the BC, the Block Transfer Protocol (RT
to BC Block transfer) as specified in section 5.5 of this document shall apply.
BUS-860/Created/T
The TM-Block (TM Source Packet) shall be read from/provided in RT subaddress 1 only.
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The RT shall indicate this Transfer type in the Transfer Descriptor Transfer Control Word
accordingly.
BUS-861/Created/T
It shall be the responsibility of the PUS terminal (RT) to manage the priority of the TM to be
transferred (e.g. to provide the functional data like attitude and position of the electrical thruster
mechanism periodically and with highest priority).
BUS-864/Created/T
Additionally a high priority transfer of event messages requiring immediate on-board reaction
shall be provided on dedicated subaddresses as defined in BUS-91.
BUS-862/Created/T
Event data shall be acquired from the RT in the Disposable Section of a Minor Frame.
BUS-865/Created/T
Event data shall be aquired using the Event Message Handling Protocol as specified in section
5.6 of this document. The length of the event data shall be restricted to 32 words of 16bit length
(one Mil-1553B-bus message).
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5.9
BepiColombo
Commanding and Data Acquisition of MMO
The MMO is connected on a dedicated Mil-1553B-bus. Therefore no constraints with respect to
other users have to be respected.
BUS-867/Created/T
Telecommands and Telemetry between MMO and MPO (DMS) shall be exchanged in form of
data blocks via the MPO-1553B-Bus.
BUS-869/Created/R
No split of Minor Frame into fixed part and disposable part is required for commanding / data
acquisition.
BUS-870/Created/T,R
The event handling shall be applied to the separation phase only where the knowledge of health
status of the MMO is required by the MPO in order to release the separation sequencer.
BUS-886/Created/T
The MMO shall be ready to accept telecommands TBD sec after power-on, even before
producing any telemetry data. After successful activation, the MMO shall enable generation of
it's default HK data block.
5.9.1
MMO Telemetry Acquisition
BUS-872/Created/T
Telemetry data blocks generated by the MMO shall be acquired by the MPO (DMS) via the
MPO-1553B-Bus.
BUS-939/Created/T
Telemetry acquisition, i.e. transfer of TM-Blocks, shall be performed in the Minor Frame with a
frequency of 1 Hz (TBC).
BUS-940/Created/T
For transmission of TM Blocks from the MMO to the BC, the Block Transfer Protocol (RT to BC
Block transfer) as specified in section 5.5 of this document shall apply.
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BUS-941/Created/T
The TM-Block (Telemetry data block) shall be read from RT subaddress 1 only.
The RT shall indicate this Transfer type in the Transfer Descriptor Transfer Control Word
accordingly.
BUS-938/Created/T
The data block shall be embedded by the MPO (CSW) into a Telemetry Source Packet compliant
with the BepiColombo packet structure definition as defined in [RD-1].
BUS-887/Created/T
All Telemetry Source packets containing the MMO telemetry data block shall be time stamped
with the SCET time (of Telemetry data block acquisition) by the MPO (CSW).
BUS-874/Created/T,R
The first 16 bit of each Telemetry data block generated by the MMO shall be used as MMO Data
Type Identifier (further called "Type-ID") to be interpreted by the MPO (CSW) as follows
(TBC):
•
Type-ID = 0dec:
Private Data
•
Type-ID <> 0dec:
Housekeeping Data
BUS-885/Created/T,R
The HK data block provided by the MMO shall contain all parameters that define the health and
safe working status of the MMO allowing monitoring of the correct operation.
BUS-875/Created/T,R
For Housekeeping Data, the Type-ID shall uniquely identify the structure of the related data
block.
Detailed definition to be agreed via MMO ICD.
BUS-881/Created/T,R
The MPO (CSW) shall use the MMO Data Type Identifier value to set the Packet Category, Type
and Subtype fields of the MPO telemetry packet containing the MMO telemetry data blocks. The
Packet Process ID shall be set to a value corresponding to the MMO spacecraft.
BUS-882/Created/T
MMO telemetry data blocks with data type identifier value set to 0 (Private Data) shall be
complemented to a Standard TM Source Packet by the MPO (CSW).
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BUS-883/Created/T
The generation of telemetry data blocks by the MMO spacecraft shall be consistent with the
acquisition rate on the MMO-1553B-Bus as defined in this document.
BUS-942/Created/T
MMO Event data shall be aquired using the Event Message Handling Protocol as specified in
section 5.6 of this document.
BUS-992/Created/T
The length of the event data shall be restricted to 32 words of 16bit length i.e one Mil-1553B-bus
message (TBC).
5.9.2
MMO Commanding
Telecommand data blocks provided by MMO will be embedded by the BepiColombo ground
segment into MPO Service 2 TC packets as per [RD-1] with the Applicaton Process ID (APID)
corresponding to the MMO.
BUS-877/Created/T
The MPO (CSW) shall extract the MMO Telecommand Data Block from the MPO TC Source
Packet and transmit it over the MMO-1553B-Bus to the MMO spacecraft.
BUS-868/Created/T
Commanding, i.e. transfer of TC Blocks, shall be performed in the Minor Frame with a
frequency of 1 Hz (TBC).
BUS-936/Created/T
For transmission of TC Blocks from the BC to the MMO, the Block Transfer Protocol (BC to RT
Block transfer) as specified in section 5.5 of this document shall apply.
BUS-937/Created/T
The TC-Block (Telecommand data block) shall be written to RT subaddress 1 only.
The Transfer type bits in the Transfer Descriptor Transfer Control Word shall be set
accordingly.
BUS-880/Created/T
The MMO shall always be able to receive, process and distribute the Telecommand data blocks
sent with the maximum data rate as specified within this document, regardless of the data block
sizes.
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BUS-888/Created/T,R
A telecommand data block shall contain one and only one telecommand function.
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6
BepiColombo
Mil-Bus FDIR (TBC)
BUS-950/Created/R
The Mil-Bus FDIR requirements apply to all BepiColombo Mil-Bus systems, i.e. MPO-1553BBus, MTM-1553B-Bus and MMO-1553B-Bus.
BUS-757/Created/A,R
No change of spacecraft redundancy configuration shall be performed on Mil-Bus FDIR
protocol level.
6.1
Error Processing on BC Hardware Level
This section focuses on the BC side processing of errors that would occur during message
transfers.
A valid data reception for a non-broadcast message requires a status response, whereas an
invalid data reception suppresses the status response but requires certain other actions. As stated
in the standard, the message command word has been validated and the error occurs in the data
word portion of the message. The withholding or suppression of the status response alerts the BC
error detection logic (no response time-out error) to the fact that an incomplete message has
occurred and some level of error recovery must occur. The setting of the message error bit in the
status word that remains in the RT will provide additional information to the error recovery logic
only if the BC requests the status word using the appropriate mode code.
Message Error bit / No response time-out: As the BepiColombo real-time message transfer is
basically built upon a continuous, sequential management of periodic transfers from/to minor
frame subaddresses, no retry nor "Transmit Status Word" mode command can be inserted.
Therefore, during the communication slots dedicated to periodic message transfers, a Message
Error bit set by an RT would not be seen by the BC. Instead, a "no response time-out" error
would be recorded by the BC hardware.
Loopback errors: Loop-back is provided that permits testing as close to the BC output as
possible (Bus Coupler not covered). Results are posted in the response block that is available to
the host. Syndrome bits are reporting command validity tests equivalent to those performed by
the RT.
BUS-964/Created/T
The BC shall check the response received to messages sent to the RT to identify and correct the
loss or corruption of a single message (e.g. occurrence of noise on the bus).
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BUS-960/Created/T
The BC shall check the response received to messages sent to the RT to detect errors that affect
a single RT / data bus interface and automatically switch to the redundant interface (if available
by bus topology).
BUS-961/Created/T
The BC shall check the response received to messages sent to the RT to detect errors that affect
a single RT irrespective of the Mil-Bus interface used and raise a corresponding event to higher
level FDIR.
BUS-962/Created/T
The BC shall check the response received to messages sent to the RT to detect errors that affect
a single BC / data bus interface and automatically switch to the redundant interface (if available
by bus topology).
BUS-965/Created/T
The BC shall check the response received to messages sent to the RT to detect errors due to
physical bus damage and switch to the redundant bus if available.
BUS-759/Created/T,R
The above shall be achieved by checking the Status Word availability and content, and the
presence of the associated data words (No checking of data word content).
BUS-231/Created/T
No retry shall automatically be attempted by the BC unless instructed otherwise by the central
software.
BUS-945/Created/T
The BC shall collect at least the following Mil-Std-1553B Status Word bit error conditions from
the RT:
•
Message Error Bit
•
Service Request Bit (as required)
•
Busy Bit
•
Subsystem Flag Bit (as required)
•
Terminal Flag Bit (as required)
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BUS-946/Created/T
The BC shall collect (and store into communication memory) the following error conditions from
the bus interface for Mil-Bus FDIR:
•
No response time-out: covering the cases when RT does not generate Status Word
following assertion of the Message Error bit.
•
BC Loopback errors: errors affecting the transmitted message detected by the BC itself
(bus coupler not covered).
•
RT response errors: errors affecting the transmitted message detected by the RT (TBC)
•
RT Status Word: Busy bit and Message Error bit with restriction regarding the Message
Error bit during periodic transfers.
BUS-947/Created/T
The following Mil-Bus FDIR related commands shall be provided for usage by on-board
functions and ground control (TBC):
•
Switch-over to bus A (nominal)
•
Switch-over to bus B (redundant)
•
Enable Mil-Bus automatic switch-over
•
Disable Mil-Bus automatic switch-over
Detailed format of these commands to be agreed via OBC Hardware/Software ICD.
BUS-952/Created/T
The BC shall provide the active/switch status of bus A / bus B to the on-board functions and
ground control.
6.2
Error Processing on BC Software Level
BUS-484/Created/A,R
The BC software shall use the errors defined in BUS-946 for determining the next FDIR action
to be undertaken.
BUS-958/Created/T
The Mil-Bus error conditions detected by the BC shall be reported to higher level FDIR.
BUS-473/Created/T
Upon error occurrence, no retry shall be attempted and the minor frame operations shall
continue until the last message transfer has been completed.
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BUS-505/Created/T
Any message that has failed - protocol or no response - shall not be retransmitted during the
same minor frame in which that message was originally sent.
BUS-483/Created/T
No "Transmit Status Word" mode command shall be issued by the BC upon "no response timeout" error during the execution of the minor frame periodic message transfers.
BUS-486/Created/T,R
The BC software shall analyse the errors logged by the BC hardware in the communication
memory (ref. BUS-946), establish a "Fault Report (most probable failure cause)" and undertake
"FDIR action on bus level" as shown in the Figure 6.2-1:
Error condition
Fault Report
(most probable failure cause)
FDIR action on bus level
For only one RT:
Loopback = OK; repeated "No response timeout" errors or "RT response errors".
Unique RT suspected;
RT fails to respond with a valid
transmission for consecutive
commands.
Complete minor frame and continue
major frame;
Suspend transfers with that RT.
For several RTs on same bus:
Loopback = OK; repeated "No response timeout" errors or "RT response errors".
Bus Coupler and bus suspected;
Common items on communication
path.
Switch to redundant bus at the latest
at next major frame keeping the
same processor on BC side.
Repeated "Loopback errors" for several RTs
Bus Controller suspected.
Report to system level FDIR.
Repeated Busy bits
RT unit
(overload, non-interruptible task, etc.)
Report to system level FDIR.
Figure 6.2-1: Recovery as a Function of 1553B Error Conditions
6.3
Mil-Bus Failure Isolation Procedure
BUS-948/Created/T
The BC shall use bus A as the default transfer medium.
BUS-949/Created/T
If bus A was used and the BC Mil-Bus FDIR function detects/isolates a bus error on bus A, an
automatic and global (all message exchange with all RTs connected to this bus) switch to bus B
shall be performed (bus reconfiguration).
BUS-951/Created/T
No automatic bus reconfiguration from bus B to bus A shall be implemented.
In other words, if a further failure is isolated on bus B, no automatic recovery shall be triggered
and the traffic shall be maintained on bus B.
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A report shall be generated and provided to higher level FDIR function.
BUS-954/Created/T,R
The isolation of the bus failure shall be an automatic procedure performed by the BC. A
simplified flow control diagram is given in Figure 6.3-1.
Major Frame cycle on Bus A
Error flag update
Evaluate
Mil-Bus Errors
No Error
Mil-Bus Error
(RT Transmision Error,
RT No-Response Time-out..)
Bus B not OK
(not usable)
Send test command on Bus B
Evaluate test
Bus B OK
Send test command on Bus A
(to eliminate spurious noise error)
Evaluate test
Bus A not OK
Bus A OK
(error disappeared)
Continue on Bus A
Switch to Bus B
Figure 6.3-1: Mil-Bus Failure Isolation procedure (simplified)
BUS-955/Created/T
For failure isolation, the BC shall sample the status of bus B via dedicated asynchronous
messages whilst the main traffic remains on bus A.
BUS-956/Created/R
A bus failure is confirmed if bus B is sampled OK whilst bus A is sampled as failed.
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Doc. No:
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EADS Astrium GmbH
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Date:
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