Two things occured to me about using the parallel port with a PC to talk
with a VMU

1. OS timing problems- is it possible to just be rude and turn off
interrupts while we run? It looks like the timing is espcially critical, but
maybe there is a slack time that we can periodically turn the interrupts
back on and let the OS do its stuff. An analysis of the VMU's firmware might
be able to find if such a slack time exists and possibly the time limit
before a time-out error.

2. If I remember right, there are some open collector outputs on the
parallel port. This could solve the 5v PC into a 3v VMU problem: Use the
VMU's 3 volt output as a voltage source for the pullup. Going the other way:
when I hooked up the VMU to an analayzer, I used default TTL levels; so if
my analyzer saw it's output levels, a parallel port should also see it.

ok. I lied. Three.

3. I guess the biggest problem is the connector. I just soldered to the
insides of a VMU, but this was sortof a pain in the neck.

Great work Soeren!

-- john

p.s. I missed about 2 days of messages right around the time Soeren first
talking about his work here. Did anyone else?


"Matthias L. Jugel" wrote:

> soeren gust <sgus-@...> wrote:
> original article:http://www.egroups.com/group/vmu-dev/?start=54
> > I have just released the first version of my PC to VM transfer
> hardware.
> > You can get it at "http://soeren.infoserv.de/vm/".
>
> while looking over your hardware descriptions:
>
> a) do you have old floppy connector cables? they have these
> connectors which look like they could work instead of
> the local bus stuff (which is unlikely to be around for
> most people)
>
> b) you can get 5V from the PS/2 connector if you need
> external power, so that might be an idea instead of
> really external power as you used. i don't know if it
> is enough though.
>
> great work :-) i will talk with out hardware guy next
> week and see if we can find an easier way to connect the
> vmu.
>
> leo.
>
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