20. Building An EEPROM Programmer (Part 1).

Please note that I have disabled comments on this post purely due to a persistent spammer - Dave 23/04/2021.

Its all very well having an EEPROM chip to store our program for the Z80, but somehow we need to get the code onto it. Enter, the EEPROM programmer. So far I have wired up the EEPROM to the Arduino Mega and I can read from it successfully. Writing to it is easy enough, but just now I can't bulk load a file to it. When I do, go find Part 2 :)

Here's a diagram I made using this great tool called Fritizing:

As you can see I've used a 74LS04 Hex Inverter to make sure the 3 control lines are HIGH by default as the pins on the Arduino are LOW by default and as the control pins are 'Active Low' we don't want data overwritten accidentally. It also means that setting the pin to HIGH in the Arduino code means the pin is Active.

Here's the EEPROM Reader code for the Arduino Mega:

/*
 EEPROM Chip Reader
*/

#define memsize 8192

int STS   = 13;  // Status Indicator

int AP[16] = {22,24,26,28,30,32,34,36,38,40,42,44,46,48,50,52};
int AD[16] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
int DP[8]  = {23,25,27,29,31,33,35,37};
int DD[8]  = {0,0,0,0,0,0,0,0};

int CE  = 4;
int OE  = 3;
int WE  = 2;

int i;
int j;
int D;
int A;

void setup() {
      
  // Setup Control Pins
  pinMode(CE, OUTPUT);
  pinMode(WE, OUTPUT);
  pinMode(OE, OUTPUT);
  
  // Disable Chip, and disable read and write.
  digitalWrite(CE, LOW);
  digitalWrite(WE, LOW);
  digitalWrite(OE, LOW);

  Serial.begin(115200);
  
  Serial.println("Reading EEPROM...");
  
  pinMode(STS,   OUTPUT);
  digitalWrite(STS,HIGH);
  
  // Setup Address Pins 
  for (i=0;i<16;i++) {
    pinMode(AP[i],OUTPUT);
  }
  
  // Setup Data Pins
  for (i=0;i<8;i++) {
    pinMode(DP[i],INPUT);
  }

  delay(1000);
  
  for (A=0;A<memsize;) {
    
    if (A<4096) Serial.print("0");
    if (A<256)  Serial.print("0");
    if (A<16)   Serial.print("0");
    Serial.print(A,HEX);
    Serial.print(" ");

    for (j=0;j<16;j++) {
    
      // Setup Address Pins
      for (i=0;i<16;i++) {
        if((A&bit(i))>0) {
          AD[i]=HIGH;
        } else {
          AD[i]=LOW;
        }      
        digitalWrite(AP[i],AD[i]);
      }
    
      digitalWrite(CE,HIGH);      // Chip Enabled
      digitalWrite(OE,HIGH);      // Read Enabled
    
      // Read Data Pins
      D=0;
      for (i=0;i<8;i++) {
        DD[i]=digitalRead(DP[i]);
        D=D+bit(i)*DD[i];
      }
    
      digitalWrite(OE,LOW);     // Read Disabled
      digitalWrite(CE,LOW);     // Chip Disabled
    
      if (D<16) Serial.print("0");
      Serial.print(D,HEX);
      Serial.print(" ");
      
      A++;
    }
    
    Serial.println();
    
  }
  
}

void loop() {
  digitalWrite(STS, HIGH);   // set the LED on
  delay(500);              // wait for a second
  digitalWrite(STS, LOW);    // set the LED off
  delay(500);              // wait for a second
}