8051 programming in C

Widely used data types for 8051 C

Data Type	Size in Bits	Data range/Usage
Unsigned char	8 – bit	0 – 255
Signed char	8 – bit	-128 - +127
Unsigned int	16 – bit	0 – 65535
Signed int	16 – bit	-32768 - +32768
sbit	1 – bit	SFR bit addressable only
bit	1 – bit	RAM bit addressable only
sfr	8 – bit	RAM addressable 80 – FF only

Some program examples using above data types.

#include<reg51.h> /*  * This function  * SEND VALUES 00 - FF TO PORT P1  *  */ void main() {                 usigned char z;                 for(z = 0; z<=255; z++)                                 P1 = z; }//end of program

#include<reg51.h> /*  * This function  * SENDS ASCII CHARS A,B,C,D,1,2,3 TO PORT 1  *  */ void main() {                 unsigned char ascii[] = "ABCD123";                 unsigned char z;                 for(z= 0; z<=7; z++)                                 P1 = ascii[z]; }//en of program

#include<reg51.h> /*  * This function  * TOGGLES BIT D0 OF PORT 1  * P1.0  */ sbit P10bit = P1^0; void main() {                 unsigned int z;                 for(z = 0; z<=someValue; z++)                 {                                 P10bit = 0;                                 P10bit = 1;                 }              }//end of program

Points to note in above examples:

1)      Try using smallest possible size of a variable to save chip space. Like for looping I used a char variable instead of an integer saving a whole byte of storage space.

2)      Sbit is used for sfr bit addressable only. It includes all sfr registers including ports and register A and B too.

3)      Including reg51.h is of course must. As it contains well in built definition for embedded type data types. This file is different for different chip, controllers and processors.

Time delay in C

There are 2 ways to create time delay in 8051 C.

1)      Using a simple for loop.

2)      Using 8051 timers.

Point to note:

When we program in assembly language we can control exact instructions and their sequences used in delay subroutine. In case of C programs, it is the C compiler that converts the C statements and functions to assembly language instruction. As a result different compliers produce different codes.

Programs related to time delay using loop:

#include<reg51.h> /*  * Toggle P1 with some delay in between  * on and off.  *  */ void main() {                 unsigned int x;                 while(1) // Repeat forever                 {                                 P1 = 0x55;                                 for(x = 0; x<80000; x++);                                 //some delay. delay size unknown                                 P1 = 0xAA;                                 for(x = 0; x<80000; x++);                 }//end of while loop }// end of main //end of program

#include<reg51.h> /*  * Create a delay of 250 ms  *  */ void msdelay(unsigned int x) {                 unsigned int i,j; //loop variables                 for(i = 0; i<x; i++)                                 for(j = 0;j<1275; j++); }//end of msdelay() void main() {                 while(1)//Repeat foreever                 {                                 P1 = 0x55;                                 msdelay(250);                                 P1 = 0xAA;                                 msdelay(250);                 }//end of while }//end of main //end of program

Points to note in loop delay:

1)      Though not accurate method for time delay. Loop method does come handy for display programming. For different chips its need to be tested with an oscilloscope. Value of 1275 works well enough for a millisecond delay. So all delay will be created using value 1275.

2)      Though I will mostly use loop delay. But it is not considered a good practice to use loop delay. It is easy to understand. So I will say try using timers. As it will be shown in coming posts.