I've got some code to use shift registers in Arduino to light up some LEDs. This is the tutorial http://www.gammon.com.au/forum/bbshowpost.php?id=11518
Everything is cool when I use Arduino's serial monitor. But I don't know how to send the same commands to Arduino from Pd cause what seems to denote the end of a command are the '\n' and '\r' characters (line feed and carriage return).
Anyone knows how to implement those in Pd?

Eventually it wasn't necessary. It's just that depending of the Arduino sketch, you might have to send ASCII values from Pd. For example if Arduino needs to receive 011, you need to send 48 49 49 from Pd.
Anyways, problem solved.

Plus I think that [comport] appends the carriage return to anything you send to it. Not exactly sure though.