Arduino Nano based program loader for 8bit CPU

#include <Arduino.h>
#include <Wire.h>
#include <SPI.h>
#include <Adafruit_SSD1306.h>
#include <Adafruit_GFX.h>

Adafruit_SSD1306 display(-1);

//control pins
#define CPU_RESET A2
#define MEM_WRITE A3
#define SR1_INPUT 2
#define SR2_INPUT 3
#define SR1_CLOCK 4
#define SR2_CLOCK 5
#define SR1_LATCH 6
#define SR2_LATCH 7

//read pins
#define CONFIRM_BUTTON A0
#define COUNTER_0 A1
#define CLOCK_STOP A6
#define PROG_MODE A7

//constants
#define PULSE_DURATION 10

//variables
int confirmButton = 0;
bool programMode = false;

//reset all modules
void resetCPU(){
 
 //CPU reset attempt#1
 //Serial.println("\nCPU Reset Signal");
 display.clearDisplay();
 display.setCursor(0,0);
 display.println("CPU Reset Signal");
 //display.display();
 digitalWrite(CPU_RESET, HIGH);
 delay(PULSE_DURATION);
 digitalWrite(CPU_RESET, LOW);

 //Check if CPU reset worked properly and repeat if necessary.
 int resetCounter = 2;
 while(digitalRead(COUNTER_0)){
  //Serial.println("CPU Reset Attempt#"+resetCounter);
  display.println("CPU Reset Attempt#"+resetCounter);
  //display.display();
  resetCounter++;
  digitalWrite(CPU_RESET, HIGH);
  delay(PULSE_DURATION);
  digitalWrite(CPU_RESET, LOW);
 }
 //Serial.println("CPU Reset Successful");
 display.println("CPU Reset Successful");
 display.display();
 delay(900);
}

//shift 4 bits to SR2 and latch to memory address register.
void setMemoryAddress(byte address){
 
 digitalWrite(SR2_LATCH, LOW);
 shiftOut(SR2_INPUT, SR2_CLOCK, MSBFIRST, address);
 digitalWrite(SR2_LATCH, HIGH);

 String outputText = "";
 for (int i = 0; i < 4; i++){
  if(address & 1)
   outputText = "1" + outputText;
  else
   outputText = "0" + outputText;
  address = address >> 1;
 }
 //Serial.print(outputText+": ");

}

//shift 8 bits to SR1 and latch to memory data.
void writeToRAM(byte data){
 
 digitalWrite(SR1_LATCH, LOW);
 shiftOut(SR1_INPUT, SR1_CLOCK, MSBFIRST, data);
 digitalWrite(SR1_LATCH, HIGH);
 
 String outputText = "";
 for (int i = 0; i < 8; i++){
  if(data & 1)
   outputText = "1" + outputText; 
  else
   outputText = "0" + outputText;
  data = data >> 1;
 }
 //Serial.println(outputText);
 pinMode(MEM_WRITE, OUTPUT);
 digitalWrite(MEM_WRITE, LOW);
 delay(PULSE_DURATION);
 pinMode(MEM_WRITE, INPUT);
}

void setup() {

 //initialize with the I2C addr 0x3C
 display.begin(SSD1306_SWITCHCAPVCC, 0x3C);  

 //clear the buffer.
 display.clearDisplay();

 display.setTextSize(1);
 display.setTextColor(WHITE);

 //initalize serial connection
 Serial.begin(115200);
 Serial.println();

 //initialize pins
 digitalWrite(CPU_RESET, LOW);
 digitalWrite(SR1_INPUT, LOW);
 digitalWrite(SR2_INPUT, LOW);
 digitalWrite(SR1_CLOCK, LOW);
 digitalWrite(SR2_CLOCK, LOW);
 digitalWrite(SR1_LATCH, LOW);
 digitalWrite(SR2_LATCH, LOW);
 pinMode(CPU_RESET, OUTPUT);
 pinMode(SR1_INPUT, OUTPUT);
 pinMode(SR2_INPUT, OUTPUT);
 pinMode(SR1_CLOCK, OUTPUT);
 pinMode(SR2_CLOCK, OUTPUT);
 pinMode(SR1_LATCH, OUTPUT);
 pinMode(SR2_LATCH, OUTPUT);
 
 pinMode(CONFIRM_BUTTON, INPUT);
 pinMode(MEM_WRITE, INPUT);
 pinMode(COUNTER_0, INPUT);
 pinMode(CLOCK_STOP, INPUT);
 pinMode(PROG_MODE, INPUT);

 //notify user to disable the clock and switch to programming mode.
 //program execution will not continue unless these conditions are satisfied.
 programMode = (analogRead(CLOCK_STOP) < 210 && analogRead(PROG_MODE) < 210) ? true : false;
 if(!programMode){
  //Serial.println("Please switch Clock to manual and Memory to programming mode.");
  display.setCursor(0,0);
  display.println("Please switch Clock\nto manual and Memory to programming mode.");
  display.display();
 }
 while(!programMode){
  programMode = (analogRead(CLOCK_STOP) < 210 && analogRead(PROG_MODE) < 210) ? true : false;
 }

 //wait for user to ensure all DIP switches are in the ON (HIGH) position. These switches
 //are inverted in Ben's design, hence moving them to the UP position disconnects them.
 
 //Serial.println("Ensure ALL DIP switches are in the ON (HIGH) position.\nPress button to continue.");
 display.clearDisplay();
 display.setCursor(0,0);
 display.println("Ensure ALL DIP\nswitches are in the\nON (HIGH) position.\n\nPress button to\ncontinue.");
 display.display();

 //loop until the user presses the button.
 confirmButton = digitalRead(CONFIRM_BUTTON);
 while(confirmButton != 1){
  confirmButton = digitalRead(CONFIRM_BUTTON);
 }

 resetCPU();
 display.clearDisplay();
 display.setCursor(0,0);

 //disable memory address dip switch input.
 //Serial.println("\nProgramming the memory");
 display.println("Programming the\nmemory");
 byte code[] = {224, 47, 116, 96, 63, 224, 128, 100, 0, 0, 0, 0, 0, 0, 0, 1};
 for (int address = 0; address < 16; address++){
  setMemoryAddress(address);
  writeToRAM(code[address]);
  display.print(".");
  display.display();
  delay(10);
 }

 //disable shift register latches, and reset all modules again.
 digitalWrite(SR1_LATCH, LOW);
 digitalWrite(SR2_LATCH, LOW);
 resetCPU();
 //Serial.println("\nPlease switch to run mode and enable the clock...");

 programMode = false;
}

void loop() {
   programMode = (analogRead(CLOCK_STOP) > 210 && analogRead(PROG_MODE) > 210) ? true : false;
 if(programMode){
  display.clearDisplay();
  display.setCursor(40,30);
  display.println("RUN MODE");
  display.display();
 }
 else{
  display.clearDisplay();
  display.setCursor(0,0);
  display.println("Please switch to run\nmode and enable the\nclock...");
  display.display();
 }
 delay(100);
}