Re: USB to IEC

Den Fri, 03 Jan 2020 12:35:21 +1300 skrev André Fachat <afachat_at_gmx.de>:
> As far as I understand the Pi does not have enough pins for an IEEE488
> interface, or does it?

If there isn't enough pins some shift register solution or other kind
of multiplexer could be built. A "PI8250" doesn't have to be cycle
exact like a PI1541 so it's a bit more flexible. We are kind of free to
do what we want right now as there afaik isn't any well known IEEE 488
HATs for the Pi. As soon as some "standard" is established we are kind
of locked-in though. It would be nice to combine IEEE-488 with a
PI1541-compatible IEC interface on the same HAT though.

Btw an Arduino has just enough pins for IEEE 488 if you only want it to
be compatible with

> How is the ATN response done in Pi1541? In the Atmega world I could
> use an interrupt for that, would the Pi be fast enough?

I think it's done in software. However for any IEEE-488 HAT it would be
simple to add an ATN trap. With an ATN trap and not having to do cycle
exact emulation, you could run the software under Linux rather than
bare bones (as the cycle exact PI1541 does) and thus have all the
filesystem stuff that's available in Linux.

Btw it might be a good idea to feature creep in an ATN trap that can be
used with an IEC interface too. That way the user could choose between
PI1541 cycle exact emulation (without network or any other processes
running as it runs bare bone) and some IEC drive emulator running under
Linux, depending on what the use case is. I'd say that the only thing
that might drive up cost of such board is PCB size and for ready-made
versions the time to assembly it. Various 74xx chips that would be used
for for example multiplexing lines to get enough lines for IEEE 488 and
74xx chips for ATN trap functionality are almost for free as compared
to the cost of the PCB, the IEEE connector and so on.

-- 
(\_/) Copy the bunny to your mails to help
(O.o) him achieve world domination.
(> <) Come join the dark side.
/_|_\ We have cookies.