DS2251T

121395 4/19

PIN ASSIGNMENT

1

P1.0

19

XTAL2

37

P0.2

55

INTB

2

P1.1

20

GND

38

P0.1

56

BD0

3

P1.2

21

P2.0

39

P0.0

57

BD1

4

P1.3

22

P2.1

40

58

BD2

5

P1.4

23

P2.2

41

BA0

59

BD3

6

P1.5

24

P2.3

42

BA1

60

BD4

7

P1.6

25

P2.4

43

BA2

61

BD5

8

P1.7

26

P2.5

44

BA3

62

BD6

9

RST

27

P2.6

45

BA4

63

BD7

10

P3.0 RXD

28

P2.7

46

BA5

64

R/W

11

P3.1 TXD

29

PSEN

47

BA6

65

PF

12

P3.2 INT0

30

ALE

48

BA7

66

PE3

13

P3.3 INT1

31

PROG

49

BA8

67

PE4

14

P3.4 T0

32

P0.7

50

BA9

68

INTP

15

P3.5 T1

33

P0.6

51

BA10

69

INTA

16

P3.6 WR

34

P0.5

52

BA11

70

SQW

17

P3.7 RD

35

P0.4

53

BA12

71

VRST

18

XTAL1

36

P0.3

54

BA13

72

BA15

PIN DESCRIPTION

PIN

DESCRIPTION

39–32

P0.0 – P0.7. General purpose I/O Port 0. This port is open–drain and can not drive a logic 1.

It requires external pull–ups. Port 0 is also the multiplexed Expanded Address/Data bus.

When used in this mode, it does not require pull–ups.

1–8

P1.0 – P1.7. General purpose I/O Port 1.

21–28

P2.0 – P2.7. General purpose I/O Port 2. Also serves as the MSB of the Expanded Address

bus.

10

P3.0 RXD. General purpose I/O port pin 3.0. Also serves as the receive signal for the on

board UART. This pin should NOT be connected directly to a PC COM port.

11

P3.1 TXD. General purpose I/O port pin 3.1. Also serves as the transmit signal for the on

board UART. This pin should NOT be connected directly to a PC COM port.

12

P3.2 INT0. General purpose I/O port pin 3.2. Also serves as the active low External Interrupt

0.

13

P3.3 INT1. General purpose I/O port pin 3.3. Also serves as the active low External Interrupt

1.

14

P3.4 T0. General purpose I/O port pin 3.4. Also serves as the Timer 0 input.

15

P3.5 T1. General purpose I/O port pin 3.5. Also serves as the Timer 1 input.

16

P3.6 WR. General purpose I/O port pin. Also serves as the write strobe for Expanded bus

operation.

17

P3.7 RD. General purpose I/O port pin. Also serves as the read strobe for Expanded bus

operation.