Sample multiplexing 7-segment LED displays on AVR

multiplex-inter-loop.cpp

//
// Sample multiplexing 7-segment LED displays on AVR
// http://blog.malcom.pl/2017/o-multipleksowaniu-wyswietlaczy-led.html
//
// Copyright (C) 2017 Marcin 'Malcom' Malich <me@malcom.pl>
//

#include <inttypes.h>
#include <stdio.h>	// size_t

#include <avr/io.h>
#include <avr/interrupt.h>


#define NO_DISPLAY_LEADING_ZEROS	1

#define LedDrive	PORTD
#define LedData		PORTC


const uint8_t SegDigitData[] = {

			// P  7654 3210
			// p  hgfe dcba
	0x3F,	// 0  0011 1111
	0x06,	// 1  0000 0110
	0x5b,	// 2  0101 1011
	0x4f,	// 3  0100 1111
	0x66,	// 4  0110 0110
	0x6d,	// 5  0110 1101
	0x7d,	// 6  0111 1101
	0x07,	// 7  0000 0111
	0x7F,	// 8  0111 1111
	0x6F,	// 9  0110 1111
	0x80,	// .  1000 0000

};

const size_t SegDigitCount = sizeof(SegDigitData) / sizeof(SegDigitData[0]);


enum Action : uint8_t {
	UpdateDisplay	= 0x01,
	UpdateCount		= 0x02,
};

volatile uint8_t ActionFlag = 0;

uint8_t ticks = 0;

ISR(TIMER0_COMPA_vect) {

	// on every ~2ms, 400Hz = 2.5
	ActionFlag |= Action::UpdateDisplay;

	// on very 100ms
	if ((ticks % 100) == 0)
		ActionFlag |= Action::UpdateCount;

	ticks++;
}

int main() {

	DDRD = 0x0F;
	DDRC = 0xFF;

	LedDrive = 0x0F;
	LedData = 0xFF;

	// interrupt on ~1kHz / 1ms
	OCR0A = 250;
	TCCR0A |= (1 << WGM01);		// clear on compare
	TCCR0B |= (1 << CS00)		// prescaler 64
			| (1 << CS01);
	TIMSK0 |= (1 << OCIE0A);	// compare a match interrupt

	sei();

	// count data
	unsigned int count = 0;

	// display data
	const size_t DigitsCount = 4;
	uint8_t digits[DigitsCount] = { 0xFF, 0xFF, 0xFF, 0xFF };
	uint8_t currDigit = 0;

	while (true) {

		if (ActionFlag & Action::UpdateCount) {
			count++;

			auto num = count;
			for (int8_t i = DigitsCount - 1; i >= 0; i--) {

				uint8_t v = num % 10;
				num /= 10;

			#if NO_DISPLAY_LEADING_ZEROS
				if (v == 0 && num == 0)
					v = ~0;
			#endif

				digits[i] = v;
			}

			ActionFlag &= ~Action::UpdateCount;
		}

		if (ActionFlag & Action::UpdateDisplay) {

			// off previous LED group
			LedDrive |= (1 << currDigit);

			currDigit++;

			if (currDigit == DigitsCount)
				currDigit = 0;

			LedData = ~SegDigitData[digits[currDigit]];

			// on current LED group
			LedDrive &= ~(1 << currDigit);

			ActionFlag &= ~Action::UpdateDisplay;
		}

	}

	return 0;
}

multiplex-interrupt.cpp

//
// Sample multiplexing 7-segment LED displays on AVR
// http://blog.malcom.pl/2017/o-multipleksowaniu-wyswietlaczy-led.html
//
// Copyright (C) 2017 Marcin 'Malcom' Malich <me@malcom.pl>
//

#include <inttypes.h>
#include <stdio.h>	// size_t

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>


#define NO_SHITTY_SWITCH			1

#define LedDrive	PORTD
#define LedData		PORTC


const uint8_t SegDigitData[] = {

			// P  7654 3210
			// p  hgfe dcba
	0x3F,	// 0  0011 1111
	0x06,	// 1  0000 0110
	0x5b,	// 2  0101 1011
	0x4f,	// 3  0100 1111
	0x66,	// 4  0110 0110
	0x6d,	// 5  0110 1101
	0x7d,	// 6  0111 1101
	0x07,	// 7  0000 0111
	0x7F,	// 8  0111 1111
	0x6F,	// 9  0110 1111
	0x80,	// .  1000 0000

};

const size_t SegDigitCount = sizeof(SegDigitData) / sizeof(SegDigitData[0]);


const size_t DigitsCount = 4;
uint8_t digits[DigitsCount] = {};
uint8_t currDigit = 0;

ISR(TIMER0_COMPA_vect) {

#if NO_SHITTY_SWITCH

	const uint8_t pos = 1 << currDigit;
	const uint8_t dig = digits[currDigit];

	LedDrive = ~pos;
	LedData = ~SegDigitData[dig];

	currDigit++;

	if (currDigit == DigitsCount)
		currDigit = 0;

#else // shitty switch

	switch (currDigit) {
		case 0:
			LedDrive = ~1;
			LedData = ~SegDigitData[digits[0]];
			currDigit++;
			break;

		case 1:
			LedDrive = ~2;
			LedData = ~SegDigitData[digits[1]];
			currDigit++;
			break;

		case 2:
			LedDrive = ~4;
			LedData = ~SegDigitData[digits[2]];
			currDigit++;
			break;

		case 3:
			LedDrive = ~8;
			LedData = ~SegDigitData[digits[3]];
			currDigit = 0;
			break;
	}

#endif
}

int main() {

	DDRD = 0x0F;
	DDRC = 0xFF;

	LedDrive = 0x0F;
	LedData = 0xFF;

	// interrupt on ~400Hz
	OCR0A = 156;
	TCCR0A |= (1 << WGM01);		// clear on compare
	TCCR0B |= (1 << CS02);		// prescaler 256
	TIMSK0 |= (1 << OCIE0A);	// compare a match interrupt

	sei();

	unsigned int count = 0;
	while (true) {

		auto num = count;
		for (int i = DigitsCount - 1; i >= 0; i--) {

			digits[i] = num % 10;
			num /= 10;
		}

		count++;
		_delay_ms(100);
	}

	return 0;
}