MICROCONTROLLER
Microcontroller is a
general-purpose device, but one that is meeting to read data performs limited
calculation on data, and contained is its environment based on these
calculations. The prime use, of Microcontroller is to control the operation of
a machine using a fixed program that is stored in and does not change over the
lifetime of the system.
The microcontroller design uses a
much more limited set of single and double byte instructions that are used to
move code and data from internal memory to the ALU. Many instructions are
coupled with pins on the IC package; the pins are “programmable” that is,
capable of having several different functions depending on the wishes of the
programmer. The microcontroller is concerned with getting data from and its own
pins: the architecture and instruction set are optimized to handle data in bits
and byte size.
Microcontroller will have much type of
bit handling instructions. It may have operational code for moving data from
external memory to CPU. Microcontroller may have one or two concerned with
rapid movement of code and data from external address.
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The Intel 8051 is an 8bit microcontroller
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1 serial port
·
2 timer
·
2 ,16 bit counter counter/timer
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3 internal and 2 external interrupts
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4kb internal ROM.
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4 number of 8 bit parallel I/O ports (32 pin).
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4 register bank.
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6 interrupt
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Maximum internal clock frequency rating is 12 MHZ
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16 bit DPTR (DPH (8)+DPL(8) )
·
16 bit PC (program counter)
·
40 pin IC (DIP).
·
128 byte internal ram
·
8051 has an on chip oscillator
Pin 1-8 port: these
pin can be configure as an input/output
Pin 9
RESET: A logic one on this pin disables the microcontroller and clears the
content of most registers.
Pin
10 RXD: Serial asynchronous communication input or serial asynchronous
communication output
Pin
11 TXD: Serial asynchronous communication input or serial asynchronous
communication clock output
Pin
12: INTO interrupt 0input
Pin13:
INT1 interrupt 1 input
PIN
14: T0 counter 0 clock input.
Pin
15:T1 counter 1clock input.
Pin
16: WR write to external RAM
Pin
17: RD Read from external RAM
Pin
18: XTAL1, XTAL2- Internal oscillator input and output .It Is an in built
oscillator which derives the necessary clock frequency for the operation
controller.XTAL1 is the input of the inverting amplifier that forms the
oscillator XTAL1 should be grounded when an external oscillator used. XTAL2 is
the output of the inverting amplifier that forms the oscillator and input to
the internal clock generator.
Pin
20: VSS - This is a GNG ground.
Pin
21-28: port 2 acts as an 8 bit bidirectional bit address able. These port pin
are configured as general input/output. It is given address in the SFR address
range.
Pin 29: PSEN If external ROM is used for storing program
then a logic 0 appears on it every time the microcontroller reads a byte
from memory. Program store enable is an active low output signal that acts as a
strobe to read external program memory.
Pin 30: ALE /PROG –The Address Latch Enable (ALE) - This pin used to
de-multiplex the address and data bus. This ALE signal is valid only for
external memory accesses.
Pin 31 EA/ Vpp - External access enable pin if held low. For execution
of program in internal memory , the
EA must be held high. By applying logic
one to the EA PIN, the micro controller will use both memories, first internal
then external.
Pin- 32-39:
These pins can be used as general inputs/outputs. Otherwise, p0 is configured as address output
(A0-A7) when the ale pin is driven high (1) or as data output when the ALE pin
driven low (0)
Pin- 40: VCC This a +5v dc supply voltage pin.
A register (accumulator)
A
register is a general- purpose memory used for storing intermediate results
obtained during operation. The accumulator has been allotted an address in the
on- chip special function register bank.
B register
Multiplication
and division can be performed only upon number stored in A and B register .for
other instruction , it can be used as
a scratch.
DPTR (Data Pointer Register)
It consist
of two separate register: DPH (Data Pointer High) DPL (Data Pointer Low) Its
instead function is to hold a 16 bit address.
PSW (Program Status word) Register
PSW is one of most important SFRS. It contains several status bit that reflected the current state of the
CPU.
Overflow Flag
Over flow flag is used to detect error in signed arithmetic
operations.
Carry Flag
Carry flag is used to detect error in unsigned arithmetic
operations.
Stack pointer (SP)
It is 8-bit wide. SP
generally starts the end of the data memory and is decremented with every PUSH
incremented with every POP. While the stack
may reside anywhere in on-chip RAM.
SFR (Special Function
Register)
SFRs are a sort of control table used
for running and monitoring the operation of the microcontroller. There are 21
addressable 8bit-bit register - A, B ,PSW, P0, P2, P2, P3, IP,IE, TCON and
SCON. The other 11 Registers to be addressed as byte are SP ,DPH,DPL,TMOD,TH0,TH1,TL0,TL1,PCON,SBUF
register.
TIMER/CONUTER
Two 16 bit timer/counter register
· timer/counter 0
· timer/counter 1
Timer - incremented every machine cycle . Counter – incremented
when there is 1 to 0 transition at its external input pin, pin T0 or T1.They
can configured in any of the four operating modes. The timer consists of two
bit register called TH and TL. A machine cycle consists of 12 oscillatory
periods. Which one selected by bit- pair (M1,M0) in register TMOD. Mode 0,1 and
2 are the same for both the
timer/counters. Mod 3 is different.
Timer 1 and timer0
The timer\counter function is selected
by C\T in TMOD register. The form
operating modes are selected by M1
, M0 in TMOD.
mode0
Timer in mode 0 is an 8 bit counter with a divided by 32
prescaler. In this node, the timer register is configured as 13 bit register .As
the count rolls over from all 1s to 0s,it reset interrupt flag TF1.The input in
enable to the Timer when TR1 =1 and
either GATE =0. The 13 bit counter can hold values between 0000 to 1FFFH in TH
and TL.
Mode1
Mode 1 is same as mode 0 ,except that the Timer register is
configured as 16 bit register.
MODE 2
MODE 2 configured the timer register as an 8bit counter (TRI) with automatic reload. Overflow from TL1
not only sets TF1, but also reloads ,TL1
with the contents of TH1, which is present by software.
Mode3
Mode3 is different for Timer 1 and Timer 0. TIMER 1 just
holds its count. It operates the same as when TR1 is set to 0.Timer 0 in mode 3
establishes TL0 and THO as two separate counter.
TMOD
The TMOD register selected the operation mode of TIMER T0
and T1.
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