> >> What about the serial port?  Can you just use the DSR (pin 5) for
> >> input and DTR (pin 1) for output?
>
> > I wouldn't know if they were configurable at that level - I've always
> > been a well-behaved programmer and used the firmware interfaces,
> > despite their reputation for being awful
>
> They are, actually. At least to some extent.
> But that requires more CPU cycles than the disk port, since the signal is
> not available at bit 7 (it is in bit 6) and sending requires not just
> banging a softswitch, but writing to a register.

Well...  Sort of.  At least setting DTR off is easy:

STZ $C09A, takes 4 cycles.  A steal of a deal.

You'd have to store #$01 into C09A to turn DTR on.   LDA #$01 STA
$c09a is just as effective, but takes two cycles longer than STZ does.

Reading isn't all that bad, LDA $C099 and AND #$40, or rotate bits to
test with the negative flag -- but either way this take 6 cycles to
do.

So, there's a lot of things that would take 6 cycles, and another 2/3
for a branch -- is this too slow for nada net?

-B
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