22MHz, Winbond W78E516B, non-'turbo' part, all written in assembly.

The problem is that the device A communication is bit-bang'ed, fairly high speed (56k), and very strict on timing. I have my serial interrupt routine enabled for most of the code, but key sections cannot be interrupted (even if the ISR just returned and did nothing).

I can try running it faster, and maybe, carefully, store bytes from SBUF as they come in _during_ the bit-banged routines...but the easiest solution is to just have a serial port that can buffer more than one byte in hardware.

Thanks though...