/* Program 8-2: Display "2018" on the seven-segment display with Edubase-V2 board
 * 
 * The four-digit seven-segment display is connected to two shift registers that
 * are connected to the microcontroller by SPI serially. The output of one shift
 * register is connected to the segment controls of all four digits in parrallel.
 * The other shift register is connected to the common cathodes of each digit
 * individually. To display one digit, the segment pattern is written to the
 * SPI first then the digit select is written next. Four digits are written 
 * sequentially. If each digit is turned on more then 50 times a second, the
 * digit will appear to be on consistently.
 */
  
#include "SPI.h"            /* use built-in SPI library */

const int slaveSelect = 17; /* slave select (SS) pin for chip select pin 17 */

void setup() {
    pinMode (slaveSelect, OUTPUT);  /* set the slaveSelect pin as output */
    SPI.begin();                    /* initialize SPI */
    SPI.setDataMode(SPI_MODE0);     /* 74HCT595 operates at Mode 0 */
}

void loop() {
    digitalWrite(slaveSelect, LOW);     /* assert SS low to the shift register of seven-segment LED */
    SPI.transfer(~0x5B);      /* write pattern 2 to the seven segments */
    SPI.transfer((1 << 3));   /* select digit 3 */
    digitalWrite(slaveSelect, HIGH);    /* deassert SS */
    delay(4);
    digitalWrite(slaveSelect, LOW);     /* assert SS */
    SPI.transfer(~0x3F);      /* write pattern 0 to the seven segments */
    SPI.transfer((1 << 2));   /* select digit 2 */
    digitalWrite(slaveSelect, HIGH);    /* deassert SS */
    delay(4);
    digitalWrite(slaveSelect, LOW);     /* assert SS */
    SPI.transfer(~0x06);      /* write pattern 1 to the seven segments */
    SPI.transfer((1 << 1));   /* select digit 1 */
    digitalWrite(slaveSelect, HIGH);    /* deassert SS */
    delay(4);
    digitalWrite(slaveSelect, LOW);     /* assert SS */
    SPI.transfer(~0x7F);      /* write pattern 8 to the seven segments */
    SPI.transfer((1 << 0));   /* select digit 0 */
    digitalWrite(slaveSelect, HIGH);    /* deassert SS */
    delay(4);
}