Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
Primitive but working code to enable Shift Out operation on MOS 6522 VIA from Arduino.
// 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
const byte ENCDEC = 53;
void setup() {
// set all digital ports to output mode
int inMin = 11; // Lowest input pin
int inMax = 54; // Highest input pin
for (int i = inMin; i <= inMax; i++)
{
pinMode(i, OUTPUT);
}
{
// set up timer on CLOCKOUT pin
pinMode (CLOCKOUT, OUTPUT);
TCCR1A = bit (COM1A0);
TCCR1B = bit (WGM12) | bit (CS10);
OCR1A = 7;
}
digitalWrite(ENCDEC, LOW);
// 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, HIGH);
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, HIGH);
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, LOW);
digitalWrite(D6, HIGH);
digitalWrite(D5, HIGH);
digitalWrite(D4, LOW);
digitalWrite(D3, LOW);
digitalWrite(D2, HIGH);
digitalWrite(D1, LOW);
digitalWrite(D0, HIGH);
}
void loop() {
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment