Making a Simple Free Running Timer with Multiplexing Display using Atmega32

In previous post, I made a simple multiplexing display example using a two-digit SSD. In this example, I gonna make a free running timer two a two-digit multiplexing seven-segment display. It will start counting from 0 to 999 seconds before it reset by itself.

Program simulation

The display is driven by delay function. Each digits are activated for only 5ms. I use Timer/Counter 0 to create timing tick.

The CPU clock is 4MHz. Clock period is,

1/4000000MHz =  250 nano seconds, or 0.00000025 second.

Timer 0 prescaler is Fosc/1024. So its Timer/Counter 0 period is,

0.00000025 second * 1024 = 256 micro seconds, or 0.000256 second.

The 8-bit TCNT0 register can store counting value up to 256. So the TOV0 occurs every,

256*0.000256 second = 0.065536 second.

To get a one second timing, I need to make a calculation of one second count. That is,

1 second count = (1 second)/(0.065536 second) = 15 counts.

Finally after the 15 counts, I will get a one-second time. Then I will need to reset the counter variable.

/*
 * m32Mux2Counting.c
 *
 * Created: 6/19/2022 3:36:14 PM
 * Author : aki-technical
 */ 
 
#include <avr/io.h>
 
/*Delay function*/
#define F_CPU 4000000UL
#include <util/delay.h>
 
int main(void)
{
    unsigned char temp=0,cnt=0;
    /*Common Cathode Display*/
    unsigned char displayData[10]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,0x07,0x7F,0x6F};
    /*PortB and PortD Output*/
    DDRC=0xFF;
    DDRD=0xFF;
	/*Select Fclk/1024*/
	TCCR0|=(1<<CS02)|(1<<CS00);
	/*Clear TOV0 flag*/
	TIFR|=(1<<TOV0);
	/*Clear Counter*/
	TCNT0=0;
    while (1) 
    {
		/*Multiplexing Display Process*/
		PORTD=0x00;
		PORTC=displayData[temp/10];
		/*Turn On Digit 1*/
		PORTD=0x01;
		/*Activate for 5ms*/
		_delay_ms(5);
 
		PORTD=0x00;
		PORTC=displayData[temp%10];
		/*Turn On Digit 2*/
		PORTD=0x02;
		/*Activate for 5ms*/
		_delay_ms(5);
 
		/*TOV0 occurs for every 0.065536 second*/
		if ((TIFR)&&(1<<TOV0))
		{
			cnt++;
			TIFR|=(1<<TOV0);
		}
 
		/*One second is equal to 15 counts*/
		if (cnt>=15)
		{
			temp++;
			cnt=0;
		}
		/*Check if it is greater than 99 seconds*/
		if (temp>99)
		{
			temp=0;
		}
    }
}
 
 

Click here to download its source file.

Schematic Diagram