Using counter 0 of ATMega32 to count external input pulses

Timer/counter 0 could operates in timer mode, or counter mode. In counter mode, the TCNT0 increase its values whenever the input pulse fed to pin PB0/T0 falling down or rising up. We can select between these to pulse transitions.

To use counter, we must work with CS02:00 of the TCCR0 register.

• Timer/Counter Control Register 0 (TCCR0)

BIT 7							BIT 0
FOC0	WGM00	COM01	COM00	WGM01	CS02	CS01	CS00

When the CS02:00 = 0x06 , then TCNT0 count the falling edge pulse clock fed to pin PB0/T0.

When the CS02:00 = 0x07, then TCNT0 count the rising edge pulse clock fed to pin PB0/T0.

TCNT0 is 8-bit wise read/write register. It counts from 0x00 to 0xFF. When its value rolls from 0xFF to 0x00, then the TOV0 flag is set.

x2

x1.5

x1

x0.5

00:00 / 00:00

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We can count any value larger than 0xFF by working with TOV0, and adding more variables with programming technique. 

In this example, I create a counter device display the counting result up to 9999.

Schematic diagram.
PortC and PortD display the 4-digit SSD.
SW2 connects the source signal GEN1
to pin PB0/T0, fed the counter 0.
MET1 roles as a pulse counter here, counting
the input signal from GEN1 whenever SW2
is closed.

Source code is here:

	#include <avr/io.h>
	#define F_CPU 4000000UL
	#include <util/delay.h>
	unsigned int counter_0=0;
	void displaySSD(void){
	unsigned char ssd[16]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,
	0x07,0x7F,0x6F,0x77,0x7C,0x39,0x5E,0x79,0x71};
	//Digit 1 1000's
	PORTD=0b00001100;
	PORTC=ssd[counter_0/1000];
	PORTD=0b00011100;
	_delay_ms(10);
	//Digit 3 100's
	PORTD=0b00001100;
	PORTC=ssd[(counter_0%1000)/100];
	PORTD=0b00101100;
	_delay_ms(10);
	//Digit 2 10's
	PORTD=0b00001100;
	PORTC=ssd[(counter_0%100)/10];
	PORTD=0b01001100;
	_delay_ms(10);
	//Digit 1 1's
	PORTD=0b00001100;
	PORTC=ssd[counter_0%10];
	PORTD=0b10001100;
	_delay_ms(10);
	}
	int main(void)
	{ unsigned int temp=0;
	DDRC=0xFF;
	DDRD=0xFF;
	TCCR0=0x07;
	TCNT0=0;
	TIFR=0x01;
	while (1)
	{
	displaySSD();
	/*When counter 0 overflow
	add 0xFF the holding register*/
	if (TIFR&0x01)
	{
	temp+=0xFF;
	TIFR=0x01;
	}
	counter_0=temp+TCNT0;
	/*Reset the display whenever
	the total pulse exceed 10000*/
	if (counter_0>=10000)
	{
	temp=0;
	counter_0=0;
	TCNT0=0;
	}
	}
	}

view raw m32Counter0pulse.c hosted with ❤ by GitHub

A screen shot of this program.

A simulation screen shot.
The counting reaches 2179 with some bugs. 

Back to main tutorial page ATMega32 tutorials in C with Atmel Studio 7.

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