i wrote implementations of the kermit protocol (and vt100 terminal emulators) for z80 cp/m machines and for the 6502-based BBC micro (both purely in assembler) way back in the mid 1980s. it was fun, and the protocol was really well documented, unlike some others i've had to deal with (i'm looking at you DDE & CORBA). oh, happy times! a bit later i wrote an implementation in C (and a bit of assembler for the interrupt-driven i/o) for the ibm pc.