Multiplexing three seven-segment TIL309 red LED displays with a MSP430 microcontroller. Counts from -99 to 999. Video: http://youtu.be/sDOHmbwP8FU

gistfile1.c

#include <msp430.h>

#define DISPLAY1    BIT4
#define DISPLAY2    BIT5
#define DISPLAY3    BIT6
#define DISPLAY_ALL DISPLAY1 | DISPLAY2 | DISPLAY3

#define LATCH_MINUS 0x0B // minus (-) on the LED display


void DisplayNumber(int num)
{
    int firstDigit;
    int secondDigit;
    int thirdDigit;

    if (num < 0)
    {
        firstDigit = LATCH_MINUS;
        secondDigit = (num / 10) * -1;
        thirdDigit = (num % 10) * -1;
    }
    else
    {
        firstDigit = num / 100;
        secondDigit = (num / 10) % 10;
        thirdDigit = num % 10;
    }

    P1OUT = firstDigit | DISPLAY_ALL;
    P1OUT &= ~DISPLAY1;

    P1OUT = secondDigit | DISPLAY_ALL;
    P1OUT &= ~DISPLAY2;

    P1OUT = thirdDigit | DISPLAY_ALL;
    P1OUT &= ~DISPLAY3;
}

int main()
{
    WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer
    P1DIR = BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6; // make port 1.0-1.6 to output

    int num = -99;

    while (num < 1000)
    {
        DisplayNumber(num++);
        __delay_cycles(80000);
    }
    return 0;
}