I can't send the number 13 from the Arduino to Pd using Arduino's Serial.write() function. Instead I'm receiving a 10. Does this have anything to do with the fact that ASCII 10 is a new line feed and ASCII 13 is the carriage return? Maybe [comport] is interpreting both values as the new line feed, just a thought.

A work around this is to use Serial.print((char)13); in the Arduino code. This did work with an Arduino UNO and my laptop, running Debian Jessie XFCE, but it failed with a Teensy 3.6 and an Ordoid-U3, running an Ubuntu 14.04 LTS image.

Both systems run Pd-0.47-1 with [comport] installed via apt-get.