Philips Semiconductors

Product specification

83C751/87C751

80C51 8-bit microcontroller family

1998 May 01

5

PIN DESCRIPTIONS

PIN NO.

MNEMONIC

DIP/

SSOP

LCC

TYPE

NAME AND FUNCTION

12

14

I

Circuit Ground Potential

24

28

I

Supply voltage during normal, idle, and power-down operation.

P0.0–P0.2

8–6

9–7

I/O

Port 0: Port 0 is a 3-bit open-drain, bidirectional port. Port 0 pins that have 1s written to them float,

interface. When this feature is activated by software, SCL and SDA are driven low in accordance

subsystem presents a 0. The state of the pin can always be read from the port register by the

program.

electrical characteristics listed in the tables that follow. While these differ from “standard TTL”

characteristics, they are close enough for the pins to still be used as general-purpose I/O in

memory as follows:

6

7

N/A

7

8

I

OE/PGM (P0.1) – Input which specifies verify mode (output enable) or the program mode.

OE/PGM = 1 output enabled (verify mode).

OE/PGM = 0 program mode.

8

9

I

ASEL (P0.0) – Input which indicates which bits of the EPROM address are applied to port 3.

ASEL = 0 low address byte available on port 3.

ASEL = 1 high address byte available on port 3 (only the three least significant bits are used).

7

8

I/O

8

9

I/O

P1.0–P1.7

13–20

15–20,

23, 24

I/O

Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. Port 1 pins that have 1s written

to them are pulled high by the internal pull-ups and can be used as inputs. As inputs, port 1 pins

that are externally pulled low will source current because of the internal pull-ups. (See DC

mode and accepts as inputs the value to program into the selected address during the program

mode. Port 1 also serves the special function features of the 80C51 family as listed below:

18

20

I

INT0 (P1.5): External interrupt.

19

23

I

INT1 (P1.6): External interrupt.

20

24

I

T0 (P1.7): Timer 0 external input.

P3.0–P3.7

5–1,

23–21

6, 4–1,

27–25

I/O

Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3 pins that have 1s written

to them are pulled high by the internal pull-ups and can be used as inputs. As inputs, port 3 pins

that are externally being pulled low will source current because of the pull-ups. (See DC Electrical

be programmed (or verified). The 11-bit address is multiplexed into this port as specified by

P0.0/ASEL.

RST

9

11

I

Reset: A high on this pin for two machine cycles while the oscillator is running, resets the device.

programming or verification purposes. The RESET serial sequence must be synchronized with the

X1 input.

X1

11

13

I

Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock generator circuits.

X1 also serves as the clock to strobe in a serial bit stream into RESET to place the device in the

programming state.

X2

10

12

O

Crystal 2: Output from the inverting oscillator amplifier.

NOTE:

(e.g., 2k

Ω).