Question

Q1. Write a delay routine for 8051 to create a delay of approximately 1 ms.

Q2. Write a routine for 8051 to create a rectangular wave (on port 2, bit 1) of 66% duty cycle using the above delay routine.

Answer 1

1.

Algorithm for a delay program of 1mS in 8051 timer :

1. Assume the processor is clocked by a 12KHz crystal.

2. Then the timer clock input will me 12KHz/12 = 1KHz.

3. hence the time taken for the timer to make one increment = 1mS

1 program for delay of 1mS DELAY: MOV R6,#250D MOV R7,#250D LABEL1: DJNZ R6,LABEL1 LABEL2: DJNZ R7,LABEL2 RET

2 GENERATING A RECTANGULAR WAVE OF 1mS /*pulse of 1mS is created on pin p1.0*/ #include<reg51.h> sbit pin=P1^0; void timer_delay(); int i; void main() {  TMOD=0X01; // MODE 1 OF TIMER O IS SELECTED     while(1)         {              pin=0;          timer_delay();          pin=1;          timer_delay(); } } void timer_delay() {         // time delay of 1mS using 12KHz crystal oscillator     TL0=0Xdb;       TH0=0Xff;       TR0=1;  while(!TF0);    TF0=0;  TR0=0; }