Atmel AT89C52 Microcontroller

Pin No

Function

Name

1

External count input to Timer/Counter 2, clock-out

T₂

P₁.0

2

Timer/Counter 2 capture/reload trigger and direction control

T₂ EX

P₁.1

3

8 bit input/output port (P₁) pins

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