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Micro 8051
1.
2. The 8051 is the original member of the MCS®-51 family,
and is the core for all MCS-51 devices. The features ofthe
8051 core are:
8-bit CPU optimized for control applications
Extensive Boolean processing (single-bit logic) capabilities
64K Program Memory address space
64K Data Memory address space
4K bytes of on-chip Program Memory
128 bytes of on-chip Data RAM
32 bidirectional and individually addressable I/O lines
Two 16-bit timer/counters
Full duplex UART
6-source/5-vector interrupt structure with two priority
levels
On-chip clock oscillator
3.
4. Block diagram of 8051 consist of
CPU
Two memory sections (Data and Program)
Input/output ports
Special function registers
Control logic
These all elements communicates using 8 bit data bus, know as
internal data bus
5.
6. 8051 consist of 40 pin
Many pins of 8051 are used for more than one function
The alternate functions are shown with green colour.
7. It consists of 8 bit arithmetic and logic unit
Associated with registers like A,B,PSW,SP.
It consist of 16 bit program counter and data pointer
It also contains set of special function registers
ALU performs arithmetic as well as logic function on 8 bit
variables
Arithmetic operations such as addition, subtraction,
multiplication and division
Logic operations such as AND,OR,XOR, rotate etc.
8. 8051 consist of 128 byte
internal RAM
It is organized into three
areas
Working Registers
Bit Addressable
General Purpose
First 32 bytes from 00H to
1FH are working registers.
They are divided into 4 banks
of 8 registers from R0 to R7
At a time only 1 bank is in
use, bits RS0 and RS1 in PSW
determine the bank in
current use.
When register bank is not
selected then can be used as
general purpose RAM.
9. 8051 provides 16 bytes of bit addressable area
It occupies RAM byte addresses from 20H to 2FH forming 128
addressable bits.
The RAM area from 30H to 7FH are called as general purpose
RAM.
10. 8051 has 4k byte internal
ROM from 0000H to 0FFFH
It is inbuilt and programmed
by manufacturer
It cannot be erased or
altered after fabrication
If the program exceed above
0FFFH then 8051
automatically fetch code
bytes from external program
memory.
11. 8051 has 32 I/O pins as 4
eight bit parallel Port
(P0,P1,P2 and P3)
All ports are bidirectional
They consist of latch, output
driver and input buffer.
Port 0 and 2 of output driver
and port 0 of input buffers
are used in access to external
memory
Pins of port3 are
multifunctional.
12.
13. Register A (accumulator)
It is an 8 bit register, which holds operand and receives result of
arithmetic instruction.
It can also be source or destination for logical operations.
Register B
In addition to accumulator, an 8 bit B-register is available as
general purpose register.
14.
15. Stack pointer is used to hold
internal RAM address that is
called top of stack
It is 8 bit wide
It is incremented before data is
stored during PUSH and CALL
It is decremented after data is
restored during POP and RET
instructions
It can reside anywhere on chip
RAM
Stack pointer is initialized 07 h
after reset.
Stack location begin at location
08h
16. It consists of High byte (DPH) and
low byte (DPL)
Its function is to hold 16 bit
address
It can be used as 16 bit data
register or two 8 bit registers
It does not have single internal
address.
17. 8051 has 16 bit program counter
Which holds address of memory location from which next
instructions is to be fetched
It can address up to 64k of memory
It automatically increments to point next instruction in program
sequence
PC is only register that does not have internal address.
18. Like other microprocessors Intel
family 8051 uses memory mapped
I/O through special function
registers that in implemented above
128 bytes of RAM
The figure shows special fubction bit
addresses
It shows all 4 I/O ports , CPU
registers, interrupt control registers,
time/counter etc
The power control is performed
between 80H and FFH
19.
20. All internal operations are
synchronized with help of clock
signal.
Clock signal is generated using
oscillator circuit.
The minimum and maximum
operating frequencies for 8051 are
typically 1 mhz to 16 mhz.
A machine cycle of 8051 consists of
6 states from s1 to s6,divided int
two phases p1 & p2.
Thus a m/c cycle consist of 12
oscillator periods from s1p1 to s6p2
in 1µsec.
During m/c arithmetic and logical
operations takes place in p1 and
internal register to register in p2.
ALE is activated twice a m/c cycle
for user accessible as external
reference
(ALE is activated during s1p2 and
s2p1, s4p2 and s5p1.
21. Execution of one cycle instruction begins at s1p2, when instruction is
latched into instruction register.
If it is two byte instruction second instruction is read during s4.
If it is one byte instruction there is still fetch at s4 but byte read is
ignored and pc Is not incremented.
Most instruction execute in one cycle, but mul, div are instructions that
take two cycles to complete.
Normally two bytes are fetched during every m/c cycle, only for MOVX it
takes 1 byte , 2 cycle for external memory.
22. 8051 has internal data and code
memory with limited memory
Memory may not be sufficient for
some applications
So their is need to connect
external ROM/EPROM and RAM to
8051
To increase capacity of memory
ROM is used as program memory
RAM is used as data memory
23. In 8051 when EA pin connected
to Vcc program fetches
addresses from 0000h to 0FFFh
are directed to internal ROM
From 1000h to FFFFh are
directed to external ROM/EPROM
And if EA pin is grounded all
addresses fetched by program
from 0000h to FFFFh are
directed to external ROM/EPROM
PSEN signal is used to activate
output enable signal of
ROM/EPROM
Port 0 is used as multiplexed
address/bus
Initial T –cycle gives lower order
8 bit address and later used as
data bus
8bit lower address is latched
using ALE signal
24. • Port 2 provides higher order 8
bit address
• The lower part of program
stores the vector addresses for
various vectors interrupt routine
•Each interrupt is assigned with
fixed location
• from figure we can see
•When the interrupt does not
use the location it is used as
general purpose memory.
•Instruction to access external
ROM/Program memory
•MOVC A,@A +DTPR
•MOVC A,@A +PC
25. 8051 can address upto 64k bytes
of external memory
MOVX instruction is used to
access external data memory.
Internal memory is divided into
three blocks lower 128 bytes ,
upper 128bytes and SFRS
Upper block and SFRS occupy
same address space 80h to FFh
Upper is accessible by indirect
addressing only
SFRs is accessed by direct
addressing
Lower is accessed by direct as
well as indirect addressing
26. Circuit diagram shows
connectivity with external data
memory.
Multiplexed address/data bus is
provided by external port 0,
external latch and ALE
Port 2 gives higher order sddress
bus
RD and WR signals selects
memory read and memory write
operations
27.
28. 8051 has 16 bit Timer/counter
registers: Timer 0 and Timer 1 both
can be used either as timers or
counters
If it is used as timer it will be
incremented after each m/c cycle
and the count rate is 1/12 of
oscillator frequency.
If frequency is 12 MHZ then timer
clock frequency will be 1 MHZ.
If it is used as counter it will be
incremented in response to 1-0
transition its corresponding external
input it takes two m/c cycles so
count rate is 1/24
Timers and counters are controlled
by TR!/0 bits in TCON
Gate bits in TMOD and INT1/0 input
pins of 8051
C/T bit register decides the
operation 0 for timer selection and
1 for counter