Use a rs485 communication module

Hi, those displays are awesome! If you don't mind me asking, how much did your 7x7 one cost?

Normal 'hardware' serial has to output on specific pins on the Original/Pico/WiFi boards (for instance look for USARTx_TX pins on http://www.espruino.com/Pico#pinout). On Puck.js it can be any pin.

However, it sounds like hardware serial won't do as you're limited to 7 or 8 bits.

Instead, you can easily use digitalPulse to send out a series of pulses. What's the baud rate of the data you're sending?

You could do something a bit like this pretty easily:

function toPulses(line, baud) {
  pulses = [];
  // stop bit
  line+="0";
  // start bit
  var lastBit = false; // start bit
  var time = 1;
  for (var x in line) {    
    var bit = line[x]!="0";
    if (bit!=lastBit) {
      pulses.push(time/baud);
      time = 0;
      lastBit = bit;
    }
    time++;
  }
  if (!lastBit)
    pulses.push(time/baud);
  return pulses;
}

var p = toPulses("1001010101010001", 9600/*baud rate*/);
digitalPulse(pin, 0, p);

So then all you need to do is set up the string you give to toPulses - start/stop bits are added automatically so you just need your 3 bits of command + x bits of data.