Analog modem emulator?

[Tony Duell]

> > 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 [1]). 

[1] 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 (!).

-tony