8031 Pins and Their Functions

1) Working power supply and ground

Vcc (40): power supply +5V±0.5V

Gnd (20): ground

2) Clock

XTAL1 (19): internal oscillator input

XTAL2 (18): internal oscillator output

Figure 2 Two clock circuits: (a) internal clock mode, (b) external clock mode.

1) Parallel I/O port 

①P0.0 — P0.7 (39-32) General I/O port P0 / A0-A7 / D0-D7.

②P1.0 — P1.7 (1-8) General I/O port P1 

③P2.0 — P2.7 (21-28) General I/O port P2 / A8-A15

④P3.0 — P3.7 (10-17) General I/O port P3 / Second function

  P3.0 (10): RXD serial port data reception

  P3.1 (11): TXD serial port data transmission

  P3.2 (12): INT0 external interrupt 0 

  P3.3 (13): INT1 external interrupt

  P3.4 (14): T0 counter/timer 0 external count pulse input

  P3.5 (15): T1 counter/timer 1 external count pulse input 

  P3.6 (16): WR external data memory write control signal

  P3.7 (17): RD external data memory read control signal

1) Control signal 

① ALE (30): Output positive pulse, 1 is valid, external address latch signal.

How does port P0 serve as both address line and data line? 

② EA (31): Input, 0 is valid, the first 4k selects the control signal of the external program memory.

How to select internal/external program memory for the first 4k? 

③ PSEN (29): Output, 0 is valid, selection signal for accessing external program memory.

④ WR (16): External data memory write control signal

⑤ RD (17): External data memory read control signal

⑥ RST (9): Input, high level is valid for 24 clock cycles, generating a reset operation.