primitive6522shiftOut.ino

// Define Arduino pin constants to correspond with MOS6522 pins
const byte CS1 = 24; // Chip Select 1
const byte CS2 = 23; // Chip Select 2
const byte RS0 = 38; // Register Select 0
const byte RS1 = 37; // Register Select 1
const byte RS2 = 36; // Register Select 2
const byte RS3 = 35; // Register Select 3
const byte RW  = 22; // Read-Write Line
const byte D0 =  33; // Data Bus 0
const byte D1 =  32; // Data Bus 1
const byte D2 =  31; // Data Bus 2
const byte D3 =  30; // Data Bus 3
const byte D4 =  29; // Data Bus 4
const byte D5 =  28; // Data Bus 5
const byte D6 =  27; // Data Bus 6
const byte D7 =  26; // Data Bus 7
const byte CLOCKOUT = 11;  // Mega 2560 clock goes to

void setup() {
  // set all digital ports to output mode
  int inMin = 11; // Lowest input pin
  int inMax = 38; // Highest input pin
  for (int i = inMin; i <= inMax; i++)
  {
    pinMode(i, OUTPUT);
  }
  {
    // set up 1 MHz timer on CLOCKOUT (OC1A)
    pinMode (CLOCKOUT, OUTPUT);
    // set up Timer 1
    TCCR1A = bit (COM1A0);  // toggle OC1A on Compare Match
    TCCR1B = bit (WGM12) | bit (CS10);   // CTC, no prescaling
    OCR1A =  7;       // output every cycle
  }  // end of setup

  // per 6522 datasheet:
  // "selected MCS6522 register will be accessed when CS1 is high and CS2 is low"
  digitalWrite(CS1, HIGH);
  digitalWrite(CS2, LOW);
  // RW switch
  delay(1);
  digitalWrite(RW, LOW);

  // first set Register Select to select ACR (1011):
  delay(1);
  digitalWrite(RS3, HIGH);
  digitalWrite(RS2, LOW);
  digitalWrite(RS1, HIGH);
  digitalWrite(RS0, HIGH);

  // then set the ACR to enable Shift Out
  // Start by zeroing the 3 relevant ACR bits (000):
  delay(1);
  digitalWrite(D7, LOW);
  digitalWrite(D6, LOW);
  digitalWrite(D5, LOW);
  digitalWrite(D4, LOW);
  digitalWrite(D3, LOW);
  digitalWrite(D2, LOW);
  digitalWrite(D1, LOW);
  digitalWrite(D0, LOW);

  // then set to Shift Out, free-running mode shift rate controlled by T2 (100):
  delay(1);
  digitalWrite(D7, LOW);
  digitalWrite(D6, LOW);
  digitalWrite(D5, LOW);
  digitalWrite(D4, HIGH);
  digitalWrite(D3, LOW);
  digitalWrite(D2, LOW);
  digitalWrite(D2, LOW);
  digitalWrite(D1, LOW);
  digitalWrite(D0, LOW);

  // now set Register Select to select T2C-L timer (1000):
  delay(1);
  digitalWrite(RS3, HIGH);
  digitalWrite(RS2, LOW);
  digitalWrite(RS1, LOW);
  digitalWrite(RS0, LOW);

  // set T2C-L timer to a value, say A0 (00100000)
  digitalWrite(D7, LOW);
  digitalWrite(D6, LOW);
  digitalWrite(D5, HIGH);
  digitalWrite(D4, LOW);
  digitalWrite(D3, LOW);
  digitalWrite(D2, LOW);
  digitalWrite(D1, LOW);
  digitalWrite(D0, LOW);

  // now set Register Select to select Shift Register (1010):
  digitalWrite(RS3, HIGH);
  digitalWrite(RS2, LOW);
  digitalWrite(RS1, HIGH);
  digitalWrite(RS0, LOW);

  // send a pattern to Shift Register (e.g. 00011000)
  digitalWrite(D7, HIGH);
  digitalWrite(D6, LOW);
  digitalWrite(D5, HIGH);
  digitalWrite(D4, HIGH);
  digitalWrite(D3, HIGH);
  digitalWrite(D2, LOW);
  digitalWrite(D1, HIGH);
  digitalWrite(D0, LOW);

  digitalWrite(CS1, HIGH);
  digitalWrite(CS2, HIGH);

}

void loop() {
}