DELAY PROGRAM

DELAY GENERATION:

• Delay can  generate i  two ways

1. Software delay
2. Hardware delay

software delay:

The delay can generate by using software.  The following program is example for software delay.

     void delay()

                       {

                    

                           int x,y;   

                           for(x=0;x<200;x++) 

                            for(y=0;y<600;y++);

                  }

hardware delay:

steps for hardware delay:

• Select TIMER 0 or  TIMER 1 In Any one of Timer Mode  i.e user choice { timer mode 0, timer mode 1 ,  timer mode 2, timer mode 3}  
• SET TMOD Register
• Load Timers  { TH0 and TLO or  TH1 and TL1 }
• Start Timer i.e   TR0 OR TR1 is SET
• Wait for timer flag over flow i.e     while(TF0 or TF1==0);
• Clear TF and TR BITS
• Delay completed.

program for hardware delay:-

void delay() 

{

 TMOD=0X01;

TH0=0X4B; 

TL0=0XFD; 

TR0=1;

 while(TF0==0); 

TR0=0;

 TF0=0; 

}

*******************************************************************

For Example  LED program:

LED'S  ARE  ON AND OFF WITH 1 SECOND DELAY.

#include<at89x51.h>  //  It is header file for 8051

void delay()     // delay function called by main

{

TMOD=0X01;

TH0=0X4B; 

TL0=0XFD; 

TR0=1;

 while(TF0==0); 

TR0=0;

 TF0=0; 

}

void main()

{

while(1)

{

P0=0XFF;   // led's are connected to P0 so LED'S  ON

 delay();  // delay for 1 sec

 P0=0X00;   // LED'S  are OFF

delay();     // Delay for 1 sec

}

}