8051 Micro-controller

Counter is very useful in embedded system because we always need something for counting events happening outside.

let’s take a example if we want to make a visitor counter for counting visitor in museum then we need a device that count person at entry gate. To make this type of device we need counter in embedded device.

• Now timers can also be used as counters counting events happening outside the 8051.
• When timer is used as a counter, it is a pulse outside of the 8051 that increments the TH, TL registers.
• TMOD and TH, TL registers are the same as for the timer discussed in timer section.
• Programming the timer in the timer section also applies to programming it as a counter except the source of the frequency.

C/T Bit in TMOD Register :

• The C/T bit in the TMOD registers decides the source of the clock for the timer.
• When C/T = 1, the timer is used as a counter and gets its pulses from outside the 8051.
• The counter counts up as pulses are fed from pins 14 and 15, these pins are called T0 (timer 0 input) and T1 (timer 1 input).

Example:

Assume that a 1-Hz external clock is being fed into pin T1 (P3.5). Write a C program for counter 1 in mode 2 (8-bit auto reload) to count up and display the state of the TL1 count on P1. Start the count at 0H.

Solution:

#include <reg51.h>

sbit T1=P3^5;

void main(void){
	
	T1=1;
	
	TMOD=0x60;
	
	TH1=0;
	
	while (1) {
		
		do {
			
			TR1=1;
			
			P1=TL1;
			
		}
		
		while (TF1==0);
		
		TR1=0;
		
		TF1=0;
		
	}
	
}

 Example:

Assume that a 1-Hz external clock is being fed into pin T0 (P3.4). Write a C program for counter 0 in mode 1 (16-bit) to count the pulses and display the state of the TH0 and TL0 registers on P2 and P1,respectively.

Solution:

#include <reg51.h>

void main(void){
	
	T0=1;
	
	TMOD=0x05;
	
	TL0=0
	
	TH0=0;
	
	while (1) {
		
		do {
			
			TR0=1;
			
			P1=TL0;
			
			P2=TH0;
			
		}
		
		while (TF0==0);
		
		TR0=0;
		
		TF0=0;
		
	}
	
}