Analog modem emulator?
ard at p850ug1.demon.co.uk
Wed Aug 10 17:21:39 CDT 2005
> > Sounds like the cards were approximately contemporary.
> That's perfectly reasonable. It could be that the Serial card was meant
> for local interfacing to serial peripherals while the Communications card
> was meant for "high-speed" telecommunications applications.
Yes. The bit-banger is fairly usless for serial input, although it's fine
for output. I suspect it was mainly used for driving a serial printer (I
first came across it with a Qume Sprint 5 hooked up to it), and Apple
used ETX/ACK protocol _because_ you then know when the peripheral is
possibly going to send something (unlike XON/XOFF when the peripheral
could send said characters at any time).
The 6850-based card is going to be a lot better for input, but it's a
more complicated and therefore expensive (I guess) card. But more
suiltable if you want to hang a terminal off the Apple (e.g. for running
the P-system ).
 As you doubtless know, the Apple P-system checks for a card in slot
3, and if it finds one, uses it (with the firmware drivers on that card)
for text I/O. Most people put an 80 column card there, the firmware of
which used the Apple keyboard for input, but there's no reason why you
can't put a serial card linked to a dumb terminal there. The manual gives
examples of how to set this up.
> I'll try to remember to check my manuals later today and see if each
> manual indicates the intended use of each card.
The bit-banger card also supports current loop operation, and the manual
gives instructions for linking it to an ASR33 (!).
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