Code:
if (Serial.available()) {
for (uint8_t i = 0; i < 5; i++) {
Serial1.write(M1Cmd[i]);
}
Serial.read();
}
this means if there is data to read on the 9600 baud port (your PC), then you write to the aldl port. you then read a single byte from the 9600 baud port (your PC) to nowhere.
this would technically work, if he is monitoring the serial data, then manually smacking a key in his serial terminal at the correct time to send the message (assisted by the fact that the write would only happen during a time when the bus was not fully saturated and the while() loop has exited)