KSI-W001-000

4

Pin Description(continued)

Port 1

: PIN 1~8 (DIP40), PIN 2~9 (PLCC44)

Port 1 is an 8-bit bi-directional I/O port with internal pullups.

Port 1 pins that have 1's written to them are pulled high by the internal pullups,

and in that state can be used as inputs. As inputs, Port 1 pins that are externally

being pulled low will source current because of the internal pullups.

Port 2

: PIN 21~28 (DIP40), PIN 24~31 (PLCC44)

Port 2 is an 8-bit bi-directional I/O port with internal pullups. Port 2 pins that have

1's written to them are pulled high by the internal pullups, and in that state can

be used as inputs. As inputs, Port 2 pins that are externally being pulled low will

source current because of the internal pullups.

Port 2 emits the high-order address byte during fetches from external Program

Memory and during accesses to external Data Memory that use 16-bit addresses

(MOVX @ DPTR). In this application it uses strong internal pullups when emitting

1's. During accesses to external data memory that use 8-bit addresses (MOVX @

Ri), Port 2 emits the contents of the P2 Special Function Register

Port 3

: PIN 10~17 (DIP40), PIN 13~19 (PLCC44)

Port 3 is an 8-bit bi-directional I/O port with internal pullups. Port 3 pins that have

1's written to them are pulled high by the internal pullups, and in that state can

be used as inputs. As inputs, Port 3 pins that are externally being pulled low will

source current because of the pullups.

Port 3 also serves the function of various special feature of the MCS-51 Family, as

listed below :

Port PIN

PIN NO.

Alternate Function

P3.0

10

RxD (Serial input port)

P3.1

11

TxD (Serial output port)

P3.2

12

INT0 (external interrupt 0)

P3.3

13

INT1 (external interrupt 1)

P3.4

14

T0 (Timer 0 external input)

P3.5

15

T1 (Timer 1 external input)

P3.6

16

WR (external data memory write strobe)

P3.7

17

RD (external data memory read strobe)

RST

: PIN 9 (DIP40), PIN 10 (PLCC44)

Reset input. A high on this pin for two machine cycles while the oscillator is

SD60C31/P SD60C51/P