serial_test.js

var SerialPort = require("serialport").SerialPort
var serialPort = new SerialPort("/home/root/tty1", {
  baudrate: 115200
});

var count = 0;

serialPort.on("open", function () {
  console.log('open');
  serialPort.on('data', function(data) {
    console.log('data received: ' + data);
	count++;
	if(count >= 6) {
	  console.log('sending A');
	  serialPort.write("A", function(err, results) {
	    if(err) console.log('err ' + err);
	  });
	  count = 0;
	}
	if(count == 3) {
	  console.log('sending B');
	  serialPort.write("B", function(err, results) {
	    if(err) console.log('err ' + err);
	  });
	}
  });
});