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@podstawek
Last active April 2, 2022 11:59
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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() {
}
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