NHD-0420CW - with Arduino (4-bit Parallel 6800)

//---------------------------------------------------------
/*
Program for writing to Newhaven Display Slim OLEDs based on US2066 controller. 
Pick one up today in the Newhaven Display shop! 
------> https://newhavendisplay.com/oled-displays/

This code is written for the Arduino Mega. Copyright (c) 2024 - Newhaven Display International, Inc.

Newhaven Display invests time and resources providing this open source code.
Please support Newhaven Display by purchasing products from Newhaven Display! 
*/
//---------------------------------------------------------

int DC = 30, E = 31, RES = 32, CS = 33;

//DB4-DB7 connected to pins 26-29 on Arduino MEGA
// R/W signal tied LOW (always write)

unsigned char text1[] = "Newhaven Display----";
unsigned char text2[] = "Slim OLED Display---";
unsigned char text3[] = "4x20 Characters-----";
unsigned char text4[] = "4-bit Parallel------";

void writeNibble(unsigned char nibble) {
  PORTA = (PORTA & 0x0F) | (nibble & 0xF0); // Mask and set upper nibble
  digitalWrite(E, HIGH);
  delayMicroseconds(1);
  digitalWrite(E, LOW);
}

void writeByte(unsigned char byte, bool isData) {
  digitalWrite(DC, isData ? HIGH : LOW); // Set DC for data/command
  writeNibble(byte & 0xF0);             // Send upper nibble
  writeNibble((byte << 4) & 0xF0);      // Send lower nibble
}

void command(unsigned char c) {
  writeByte(c, false);
  delayMicroseconds(40); // Small delay for command
}

void data(unsigned char d) {
  writeByte(d, true);
  delayMicroseconds(40); // Small delay for data
}

void output() {
  command(0x01);
  delay(2);
  for (int i = 0; i < 20; i++) data(text1[i]);
  command(0xA0);
  for (int i = 0; i < 20; i++) data(text2[i]);
  command(0xC0);
  for (int i = 0; i < 20; i++) data(text3[i]);
  command(0xE0);
  for (int i = 0; i < 20; i++) data(text4[i]);
}

void setup() {
  DDRA = 0xF0; // Configure upper 4 bits of PORTA as output
  PORTA = 0x00;
  DDRC = 0xFF;
  PORTC = 0x00;
  pinMode(RES, OUTPUT);
  pinMode(DC, OUTPUT);
  pinMode(E, OUTPUT);
  digitalWrite(RES, HIGH);
  delay(10);

  command(0x2A);
  command(0x71);
  data(0x00);
  command(0x28);
  command(0x08);
  command(0x2A);
  command(0x79);
  command(0xD5);
  command(0x70);
  command(0x78);
  command(0x09);
  command(0x06);
  command(0x72);
  data(0x00);
  command(0x2A);
  command(0x79);
  command(0xDA);
  command(0x10);
  command(0xDC);
  command(0x00);
  command(0x81);
  command(0x7F);
  command(0xD9);
  command(0xF1);
  command(0xDB);
  command(0x40);
  command(0x78);
  command(0x28);
  command(0x01);
  command(0x80);
  command(0x0C);
  delay(100);
}

void loop() {
  output();
  while(1);
}