Modbus Serial RTU CRC Algorithm

crc.js

var data;
process.stdin.on('data', function(chunk) {
  data = chunk
});
process.stdin.on('end', function() {
  console.log(data);
  var givenCrc = data.slice(data.length-2);
  givenCrc = (data[1] << 7 | data[0]);
  console.log(givenCrc);
  var calculatedCrc = CRC(data.slice(0, data.length -2));
  console.log(calculatedCrc);
});
process.stdin.resume();


var POLY = 0xA001;
var SEED = 0xFFFF;
function CRC(buffer) {
  var crc = SEED;
  for (var i=0; i<buffer.length; i++) {
    crc = Calc_CRC(buffer[i], crc);
  }
  return crc;
}
function Calc_CRC(b, crc) {
  crc ^= b & 0xFF;
  for (var i=0; i<8; i++) {
    var carry = crc & 0x0001;
    crc>>=1;
    if (carry) crc ^= POLY;
  }
  return crc;
}