On Aug 15, 4:58 pm, "Michael J. Mahon" <mjma...@aol.com> wrote: > Your IIc+ is *exactly* an Apple II with a built-in 4MHz Zip Chip, so > your experience applies in the case of the Zip Chip. Yes, but... the serial hardware in a IIc+ is a little different situation than a physical SSC. I'm still interested to know what other accelerated situations cause the problem.