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at89c51 microcontroller description
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AT89C51 MICROCONTROLLER

AT89C51 is an 8-bit microcontroller and belongs to Atmel's 8051 family. AT89C51 has 4KB of Flash programmable and erasable read only memory (PEROM) and 128 bytes of RAM. It can be erased and program to a maximum of 1000 times.

In 40 pin AT89C51, there are four ports designated as P1, P2, P3 and P0. All these ports are 8-bit bi-directional ports, i.e., they can be used as both input and output ports. Except P0 which needs external pull-ups, rest of the ports have internal pull-ups. When 1s are written to these port pins, they are pulled high by the internal pull-ups and can be used as inputs. These ports are also bit addressable and so their bits can also be accessed individually.

 Port P0 and P2 are also used to provide low byte and high byte addresses, respectively, when connected to an external memory. Port 3 has multiplexed pins for special functions like serial communication, hardware interrupts, timer inputs and read/write operation from external memory. AT89C51 has an inbuilt UART for serial communication. It can be programmed to operate at different baud rates. Including two timers & hardware interrupts, it has a total of six interrupts.

 

Pin Diagram:

 

                     AT89C51 Microcontroller Pin Diagram

  

 

Pin Description: 

 

Pin No

Function

Name

1

8 bit input/output port (P1) pins

P1.0

2

P1.1

3

P1.2

4

P1.3

5

P1.4

6

P1.5

7

P1.6

8

P1.7

9

Reset pin; Active high

Reset

10

Input (receiver) for serial communication

RxD

8 bit input/output port (P3) pins

P3.0

11

Output (transmitter) for serial communication

TxD

P3.1

12

External interrupt 1

Int0

P3.2

13

External interrupt 2

Int1

P3.3

14

Timer1 external input

T0

P3.4

15

Timer2 external input

T1

P3.5

16

Write to external data memory

Write

P3.6

17

Read from external data memory

Read

P3.7

18

Quartz crystal oscillator (up to 24 MHz)

Crystal 2

19                               

Crystal 1

20

Ground (0V)

Ground

21

8 bit input/output port (P2) pins

/

High-order address bits when interfacing with external memory

P2.0/ A8

22

P2.1/ A9

23

P2.2/ A10

24

P2.3/ A11

25

P2.4/ A12

26

P2.5/ A13

27

P2.6/ A14

28

P2.7/ A15

29

Program store enable; Read from external program memory

PSEN

30

Address Latch Enable

ALE

Program pulse input during Flash programming

Prog

31

External Access Enable;  Vcc for internal program executions

EA

Programming enable voltage; 12V (during Flash programming)

Vpp

32

8 bit input/output port (P0) pins

 

Low-order address bits when interfacing with external memory

P0.7/ AD7

33

P0.6/ AD6

34

P0.5/ AD5

35

P0.4/ AD4

36

P0.3/ AD3

37

P0.2/ AD2

38

P0.1/ AD1

39

P0.0/ AD0

40

Supply voltage; 5V (up to 6.6V)

Vcc