consul-vdx-term-keyboard-converter/terminal_keyboard_emulator.ino

#include <TimerOne.h>

// config:
const int pinData = 6;
const int pinStatus = 7;

// fixed values 
const int timerDelay = 500;

void setup(void)
{
  pinMode(pinData, OUTPUT);
  digitalWrite(pinData, HIGH);
  
  Timer1.initialize(timerDelay);
  Timer1.attachInterrupt(clockCycle);
  Timer1.stop();
    
  pinMode(pinStatus, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(pinStatus), statusCycle, CHANGE);
  
  Serial.begin(9600);
}

volatile long lastChange = 0;
volatile int x = 0;
volatile int dataWord = 0;
volatile int dataState = 0;
volatile int dataDelay = 0;
volatile int packetDelay = 0;
volatile int packetTail = 0;
volatile int clkState = HIGH;

volatile bool nextKeyReady = false;
volatile byte nextKey = 0;

void typeKey(byte key) {
    noInterrupts();
    nextKeyReady = true;
    nextKey = key;
    interrupts();
}
    
void sendKey(byte key) { 
    noInterrupts();
    dataWord = key;
    dataState = 8;
    dataDelay = 0;
    packetDelay = 0;
    packetTail = 10;
    clkState = HIGH;
    interrupts();
    Timer1.initialize(timerDelay);
    Timer1.start();
}

void statusCycle() {
  long timeNow = millis();
  long changeDiff = timeNow - lastChange;
  lastChange = timeNow;
  if (changeDiff >= 10 && nextKeyReady) {
      sendKey(nextKey);
      nextKeyReady = false;
  }
}

void clockCycle(void)
{
  int dataBit = HIGH;
  if (clkState == LOW) {
    clkState = HIGH;
  } else {
    clkState = LOW;
  }
  if (packetDelay > 0) {
    packetDelay--;
  } else if (dataDelay > 0) {
    dataDelay--;
    dataBit = LOW;
  } else if (dataState > 0) {
    int bitToSend = (dataWord >> (dataState - 1)) & 1;
    dataBit = !bitToSend ? LOW : HIGH;
    dataState--;
  } else if (packetTail > 0) {
    packetTail--;
    dataBit = LOW;
  } else {
    Timer1.stop();
  }
  digitalWrite(pinData, dataBit);
}

void loop(void)
{
  delay(50);

  if (Serial.available() > 0) {
      long key = Serial.parseInt(SKIP_ALL);
      if (key != 0) {
	typeKey(key);
      }
  }
}