Antoine,
Thanks for posting the listing of the various $C02D bits from the IIGS
Firmware Reference. It's more instructive than my rambling narrative and may
spur others who were not previously aware to try the technique for printer
switching purposes.
I modify (either clear or set) bit 1 to switch between a parallel printer
card and the internal serial port in slot 1.
I've found I can switch back and forth (and back) without problem provided
the slot is initially set in the Control Panel to the internal port. If it's
initially set to 'Your Card', I experience trouble (no output).