Ioannis,
Nah, it should be doable with the 18F series - I'm almost there now. Like I said earlier I have a comercially available drive that is based on the 18F2431 and it works fine, step-rate specified to 400kHz (not verified) and USB interface thru some FTDI-chip.

I've got the code from AN744 working "inside" a very simple PBP program - 5 lines of PBP code and 200 lines of ASM. Now I only need to figure out HOW it works so I get it to do what I need. I may opt for interrupt driven RX and polled TX though.

Anyway, I think I'll start a separate thread for that...

Thanks!
/Henrik.