Quote of the day
“Learn from yesterday, live for today, hope for
tomorrow. The important thing is to not stop
questioning.”
― Albert Einstein, Relativity: The Special and the General Theory
Microprocessors and Microcontrollers
• Microprocessor: general-purpose CPU
– Emphasis is on flexibility and performance
– Generic user-interface such as keyboard, mouse,
Memory etc.
– Used in a PC, PDA, cell phone, etc.
• Microcontroller: general-purpose CPU + memory
+ timer circuit on a single chip(application
oriented manufacturing)
– Emphasis is on size and cost reduction.
– The user interface is tailored to the application, such
as the buttons on a TV remote control.
– Used in a digital watch, TV remote control, car and
many common day-to-day appliances.
• Microcontroller architecture refers to the
internal hardware organization of a
microcontroller.
• It determines how and when various
operations are performed by the
microcontroller.
• Each hardware architecture has its own set
of software instructions called assembly
language that allows programming of the
microcontroller.
• Harvard Architecture—a type of computer
architecture where the instructions (program
code) and data are stored in separate memory
spaces
– Example: Intel 8051 architecture
• Von Neumann Architecture—another type of
computer architecture where the instructions
and data are stored in the same memory space
– Example: Intel x86 architecture (Intel Pentium, AMD
Athlon, etc.)
• Some of the popular microcontroller
architectures
– Intel 8051
– Zilog Z80
– Atmel AVR
• The Intel 8051 is a very popular general purpose
microcontroller widely used for small scale
embedded systems.
• Many vendors such as Atmel, Philips, and Texas
Instruments produce MCS-51 family
microcontroller chips.
• In recent years some companies have
incorporated many different and additional
features into 8051.
• The 8051 is an 8-bit microcontroller with 8 bit
data bus and 16-bit address bus.
• Address bus is a group of 16 lines used to carry
address of memory(where data is stored) /
address of the device(communicating with
microcontroller device).
• Data bus is a group of 8 lines used to carry 8-bit
data from one section to another section
internally or from microcontroller to the other
device interfaced to it.
• The 16 bit address bus can address a 64K( 216)
byte code memory space and a separate 64K
byte of data memory space.
• The 8051 has 4K on-chip read only code memory
and 128 bytes of internal Random Access
Memory (RAM)
• A group of filp-flops is referred as register in
digital circuits, which holds the data temporarily.
• A group of lines on which information is
transferred from one place to other is termed as
bus.
External interrupts
Interrupt
Control
On-chip
ROM for
program
code
Timer/Counter
On-chip
RAM
(SFR)
Timer 1
Timer 0
CPU
OSC
Bus
Control
4 I/O Ports
P0 P1 P2 P3
Address/Data
Serial
Port
TxD RxD
Counter
Inputs
• The crystal frequency is the basic
internal clock frequency.
• Clock is the smallest interval of time
required to accomplish any simple
instruction.
• Serial communication always needs
dictate the clock frequency because of
internal requirement to yield
standard baud(Bit per second) rate.
OSC
Crystal or
Ceramic
Resonator
Central processing unit (CPU)
• Arithmetic logic unit
(ALU) which
performs arithmetic
and logic functions.
• Registers A and B.
• Program Counter
(PC) and DPTR (Data
pointer.
• Program status word.
• 4-8-bit register bank
available from RAM.
Arithmetic and
Logic Unit
A
B
PC
DPTR
DPH
DPL
Address Bus
PSW
8 BIT
DATA /
ADDRESS
BUS
RAM/
ROM
• The 8051 has various 34 8-bit general purpose,
Registers. Of these the two Accumulator (A)
and B registers.
• Registers A and B are used in holding results of
mathematical and logical operations
performed by CPU.
• The accumulator register is the most useful
register apart from arithmetic and logical
operations it is also used in many data transfer
and bit manipulation operations.
• The B register is used along with A for
multiplication and division operations.
• The other 32 are arranged as part of internal
RAM in Four Banks, B0-B3 of 8-registers each.
• The ALU performs one 8-bit operation at a
time.
• The arithmetic operations such as addition/
subtraction/multiplication/division and logical
AND, OR, NOT and XOR are performed by ALU.
• The CPU has many important registers. The
Program Counter (PC) is one of this, always holds
the code memory location of next instruction to
be executed.
• It is the only register that does not have address.
• MCU fetches instructions from the code memory
pointed by PC analyzes the opcode of the
instruction.
• And updates the PC to the location of next
instruction, fetches the operand from the data
memory if necessary, and finally performs the
operation instructed by the instruction.
• Fetch operation—retrieves
an instruction from the
location in code memory
pointed to by the program
counter (PC)
• Execute operation—
executes the instruction that
was fetched during the fetch
operation. In addition to
executing the instruction,
the CPU also adds the
appropriate number to the
PC to point it to the next
instruction to be fetched.
Program
Counter
(PC)
Code Memory
F
e
t
c
h
+
CPU
To other
peripherals
• The DPTR is made of two 8-bit registers, DPH
and DPL, are used to furnish memory
addresses for internal and external code
(Program) access and external data access.
• The DPTR is used by programmer through
instructions.
• DPH and DPL are assigned separate address,
DPTR does not have a single internal address.
• Program status word—PSW(8 bit-Flag register)
– Shows the status of arithmetic and logical operations using
multiple bits
– They indicate some conditions that result after an
execution of instruction.
bit 7
CY
•
•
•
•
•
bit 6
AC
bit 5
F0
bit 4
RS1
bit 3
RS0
bit 2
OV
bit 1
--
bit 0
P
P: parity check flag
Bit1: Reserved for future use.
OV: ALU overflow flag
RS0/RS1: Register bank specification mode
00: bank 0 (00H-07H); 01: bank1(08H-0FH); 10: bank 2(10H17H); 11: bank 3(18H-1FH)
• F0: User defined flag
• CY: ALU carry out
• AC: ALU auxiliary carry out(Carry from bit 3 to bit 4 of ALU)
• Carry Flag(CY):- This flag is set whenever a
carry out from D7 bit is generated. This bit is
affected after addition and subtraction
operations.
• Auxiliary carry (AC):- If there is a carry from
D3 to D4 bit during an addition or subtraction
operation then this bit is set to one.
• Parity flag(P):- Parity flag represents the
number one’s in accumulator register. It is set
to 1 for odd number of one’s in A.
• Overflow flag(OV):- Set to one to represent
erroneous result after arithmetic operations
• Register bank specification (RS0 and RS1):D3 and D4 together used to change the
register bank to be used out of four.
There are four register banks and each bank
consists of 8-registers R0 to R7.
• Selection mode
RS1
RS0
Register Bank
Address
0
0
Bank 0 selected
00H-07H
0
1
Bank 1 selected
08H-0FH
1
0
Bank 2 selected
10H-17H
1
1
Bank 3 selected
18H-1FH