This is a short description of how I managed to develop MiniMAC:

  I got a description of what an emulator should do. A modified
  version of this can be found in eurocrypt.txt.

  I then took the source for season95, which contains a lot
  of useful routines. Especially it contains routines to
  do the serial communication. Season95 also serves as a good 
  skeleton for the program logic ie. the loop that fetches instruction
  headers and carries out the right functions.

  When I doubt on some of the instructions I looked at debug
  output from Maccess and/or Voyager to see the responces from
  these programs to the various instruction types.

  When in more doubt I looked a disassembled PIC software. This is
  also a good source for working encryption keys.

  You will then need a DES inplementation. You can find
  plenty of these on the net. 

  It was what I'll describe as a glorious moment, when MiniMAC
  actually descrambled a channel for the first time.