CoCoDuino_Int_RAM.ino

/* This sketch emulate a byte of RAM on the CoCo bus. */
/* The single byte is located in the SCS range: FF40 to FF5f */

#define SCS 0
#define RW 1

volatile unsigned int value = 255;
const int data_bus[] = {15, 22, 23, 9, 10, 13, 11, 12};

void setup() {

  /* setup data bus as input */
  for( unsigned int i=0; i<8; i++ ) {
    pinMode(data_bus[i], INPUT);
  }
  
  pinMode(SCS, INPUT);
  pinMode(RW, INPUT);

  pinMode(SCS, INPUT);
  attachInterrupt(SCS, check_io, FALLING);
  attachInterrupt(SCS, z_state, RISING);
}

void loop() {
}

void check_io() {
  if (digitalRead(RW)) {
    for( unsigned int i=0; i<8; i++ ) {
      pinMode(data_bus[i], OUTPUT);
    }

    GPIOC_PDOR = value;
  }
  else {
    value = GPIOC_PDIR & 0xff;
  }
}

void z_state()
{
  GPIOC_PDOR = 0;
  for( unsigned int i=0; i<8; i++ ) {
    pinMode(data_bus[i], INPUT);
  }  
}