====== Serial Protocol ======

For the communication between the host (PC) and the controller (Arduino), there is a serial protocol over USB.
The protocol is line by line, with carriage return ("\n") as end.
The first character denotes the type of command or information.
The following commands have been defined:

  * **C**ounter - set, read or inform about the program counter
  * **P**rogram - fills a program slot