ECE 493T9
Real Time Embedded System
Tutorial Set 3
June 10, Spring 2008
Basic ES Peripherals
• Timer / Counter
Intel 8253, MC62830, Timer Processors, Real-Time Clocks.
• Serial Ports
SPI, I2C, M-Bus, RS232
• Parallel Port
• DMA (To Be Covered in the future if needed)
Timers
•
A Must-Have for all the Synchronous Operations.
•
Pre-scalar:
Divide the clock freq. down to the
desired counting freq.
•
Phase-Lock Loop:
Multiply the clock freq. up to the desired
counting freq. Often available in FPGA.
•
•
Counter
I / O Control
Can provide more functionalities than
just a timer interrupt generator.
•
Characterized by 2 Properties:
1) Pre-scalar Value (Min Clock Freq.)
2) Counter Size
Intel 8253 Timer
• 5 Modes
•
•
•
•
•
Mode 1: Interrupt on Termination Count
Mode 2: Programmable One-Shot
Mode 3: Rate Generator (Pulse Generator)
Mode 4: Square-Wave Generator – Software Generated Strobe
Mode 5: Square-Wave Generator – Hardware Generated Strobe
• When Interrupts are generated from the Intel 8253 Timer, the
interrupt signal does not have a dedicated output pin; instead, the
OUT pin is often used as the interrupt output pin.
MC62830 Timer
• 24bit Timer
• Higher Resolution than Intel 8253
• 5bit Pre-Scalar
Drawback:
• Designed to work with 8-bit
processors => loading the timer
requires 4 cycles:
1) Load 3 8-bit preload registers
2) Reset Z flag to start countdown
Timer Processor
• Just like memory management and graphic processing, the timing
operation can also get “emancipated” from the mother CPU, giving
rise the Timer Processor.
• Design Note:
Use it only when your design really
requires a pinpointing timing!!
Each addition of an applicationspecific processor means an
additional burden on your design
budget.
Real-Time Clocks
• Rather than generating clock counts from timers, RT clocks keep
track of timing in terms of current time and date.
• With modern microprocessors running at MHz range, RT clocks can
also be software simulated to effectively reduce the design cost.
Serial Ports
• Dominant data transfer method from ES to its peripherals
• Two interconnected shift registers
• Sync. and Async.
Serial Peripheral Interface (SPI)
• By Motorola
• Synchronous Master-Slave System.
Inter-IC Bus (I2C)
• Developed by Philips in the 80s for IC
components communication in TV.
• Two-line serial bus (SCL, SDA) with
Master / Slave Communication Mode.
• Serial Control Line: (SCL)
Carries controlled clock signal, used for both
synchronizing and flow control.
• Serial Data and Address: (SDA)
Carries address and data; used in combination with
SCL to facilitate flow control.
• Basic Flow Control Mechanism:
Inter-IC Bus (I2C)
• Three Main Data Transfer Modes:
– Read Byte with ACK
– Write Byte with ACK
– Write Byte with STOP
Inter-IC Bus (I2C)
• Multiple Slave Access:
How to access a specific slave? Transfer Address before Data!!
• Basic Access Procedure:
• Extended Address Access Procedure:
Inter-IC Bus (I2C)
• Other Issues:
– Multi-Register Transfer
•
•
Inheritant Address Increment
Write Index
– ACK Flag Timing Issue
•
I2C Masters would need a timer to determine the length of a valid ACK flag.
– Multi Master Access Regulation
•
When two or more masters are on the bus, they generally monitor the bus and wait until it’s
clear before they attempt to initiate any bus activity.
Recommended Standard 232
• Implemented with DSub9 port.
• CMOS or TTL Voltage Standard.
– +5V and -5V
– +12V and -12V
– Logical Voltage Tolerance: ±2V
• RS232 is the physical interface on top of which serial transmission is
facilitated via serial protocols(ex. DF1, ModBus, etc.).
• Basic RS232 Packet (by Physical Layer Definition, ref. OSI Model)
Recommended Standard 232
• Async. Flow Control Signal Lines
• Fact:
- The layout is outdated for most applications nowadays, since RS232 has not been used
as a networking infrastructure for more than a decade.
- Instead of utilizing all 9 lines, only TxD and RxD are being used for point-to-point data
transfer – Very similar to USB.
- Occasionally, some specialized chips (such as a CANbus Interface Chip ELM232 I’ve
used for my FPGA project) would require RTS / CTS to facilitate simple handshaking
- The rest signal lines are rarely used in new ES’s. If you ever need to use them, reference
materials are all over the internet for grab.
Recommended Standard 232
• How to Implement RS232 Interface?
– Most uC’s come with at least one async. channel.
– Connect the async. channel to a RS232 physical driver chip in order to conform
to the voltage standard.
• How about USB?
•
As mentioned previously, most USB chips have
similar interface as the RS232 driver chip.
About the Project…=( =( =(
• Until we are 100% sure the dev kit will arrive in time, we
will not have a tutorial on Atmel Processor User Manual.
• One thing I’m sure about the project:
It’s a simple design project without much
constraints on the end-product to be delivered.
• It doesn’t mean that you get to hand in a first-year level
design!! It also doesn’t mean that the professor will be
extra lenient on marking!!
• Base your designs on RTOS concepts taught in this
course to earn a decent mark.
Questions?
Questions?
Questions?