INPUT OUTPUT PROGRAMMING OF 8051

As we know that 8051 has 4 ports . These ports can be used as simple input output ports.

When we want to use any pin of any port as input we have to write 1 to its corresponding latch

And for output we have to write 0 .

When any pin is written 1 it serves 5v to the external hardware and when 0 serves 0V.

                         Input output programing in C

This program will toggle all the ports after 1 sec and this task will be repeated infinite times

#include<reg51.h>                    \\header file for 8051

void delay(unsigned int);         \\function prototype

void main()                                 \\intializing the main function

{

While(1)                                      \\super loop

{

P0=0x00;                                       \\write  0 to all pins of port0

P1=0x00;                                        \\write  0 to all pins of port1

P2=0x00;                                         \\write  0 to all pins of port2

P3=0x00;                                          \\write  0 to all pins of port3

delay(1000);                                   \\1 sec delay

P0=0xff;                                             \\write 1 to all pins of port0

P1=0xff;                                             \\write 1 to all pins of port1

P2=0xff;                                              \\write 1 to all pins of port2

P3=0xff;                                              \\write 1 to all pins of port3

}}

\\delay subroutine

void delay(unsigned int x)

{

unsigned int i,j;

for(i=0;i<x;i++}{

for(j=0;j<1275;j++);

}}

Port 3 is also used for special functions. These are written below

3.0                 RXD                used to receive data serially

3.1                 TXD                 used to transmit data serially

3.2                 INT0               external interrupt 0

3.3                 INT1                external interrupt1

3.4                 T0                    input pin for timer0

3.5                 T1                     input pin for timer1

3.6                 WR                  write signal for external memory

3.7                 RD                    read signal for external memory