I/O Port Programming Using Embedded C

1.Sending 00H to FFH to Ports

#include <reg51.h>
void main(void)
{
unsigned char z;
for (z=0;z<=255;z++)
P1=z;
}
Caution
1. Pay careful attention to 
the size of the data.
2. Try to use unsigned char
instead of int if possible.

2.Sending ASCII Characters to Ports

Statement: Write an 8051 C program to send hex values for ASCII characters of 
0, 1, 2, 3, 4, 5, A, B, C, and D to port P1.
Program
#include <reg51.h>
void main(void)
{
unsigned char mynum[]=“012345ABCD”;
unsigned char z;
for (z=0;z<=10;z++)
P1=mynum[z];
}

3.Toggle Port Bits

Write an 8051 C program to toggle all the bits of P1 continuously.

Solution:

//Toggle P1 forever

#include <reg51.h>

void main(void)

{

for (;;)

{

p1=0x55;

p1=0xAA;

}

}

4.Sending values to Port

Write an 8051 C program to send values of –4 to +4 to port P1.

Solution:

//Singed numbers #include <reg51.h> void main(void)

{

char mynum[]={+1,-1,+2,-2,+3,-3,+4,-4}; unsigned char z; for (z=0;z<=8;z++)

P1=mynum[z];

}

5.Toggle Single Bit

Write an 8051 C program to toggle bit D0 of the port P1 (P1.0) 

50,000 times.

Solution:

#include <reg51.h>

sbit MYBIT=P1^0;

void main(void)

{

unsigned int z;

for (z=0;z<=50000;z++)

{

MYBIT=0;

MYBIT=1;

}

}

6.Toggle Bits with Delay

Write an 8051 C program to toggle bits of P1 continuously forever 

with some delay.

Solution:

//Toggle P1 forever with some delay in between “on” and “off”

#include <reg51.h>

void main(void)

{

unsigned int x;

for (;;) //repeat forever

{

p1=0x55;

for (x=0;x<40000;x++); //delay size 

//unknown

p1=0xAA;

for (x=0;x<40000;x++);

}

}