Hi!
One solution to consider, besides a bunch of small CPU's of personal
choice each having USB-interface and N signals I/O (thus requiring some
USB-hub's), or alternatively using the same way of thinking, but a
CAN-bus starting with a RS-232 to CAN converter from the PC would be:
Use the PC parallel port (bidirectional). For output, have a decoding
circuit (in plain logic or in an embedded CPU of favourite...) and the
required number of 8-bit latches. Use a RESET control signal to reset
the counter, thereafter sending out 8-bit words on D0-D7, having the
strobe select the proper latch to take next strobe to store the data.
This will not look like a shift-register, but more like a parallel
printer... 64 bit to write out would require 8 writes. One could also
imagine a "general" card with "LPT-in" and "LPT-out" that after reset
swallows the first 4 characters to come (and make 32 bits available for
outputs) and sends the rest of a stream "down the line". Next card in
line would take the first 4 characters that arrive into it ...
The cards would be identical to each other to design!
For input, a similar method might be usable, but here, I'm not sure
which signal to use for strobing "next register".
This should all be quire reasonable to implement though!
In the good old days. Texas instruments made the 9995 CPU, which I
think had some kind of serial 1-bit I/O-interface bus, and they sold
quite some different I/O-chips to attach. I never really learnt how this
was designed and set-up, but friends of mine who played with these
things were impressed (by then). I don't know how much of this that is
still available to the open market of electonics... If anyone else in
the list can give a 30 s class, I'd really appreceate it!
All my best,
Göran
On 2010-12-07 16:05, Pontus Pihlgren wrote:
On Tue, Dec 07, 2010 at 09:21:43AM -0500, Ken Cornetet wrote:
Keep in mind that the printer port on regular old PCs can be used for a few
lines of general input and output. I used to do this on a regular basis back in
the DOS days. Looks easy under linux too:
http://www.faqs.org/docs/Linux-mini/IO-Port-Programming.html
It's a solution I'm considering, but I have a concern. Besides the
PDP-15 panel I also have a PDP-12 panel. The PDP-12 panel has arround
120 lights. So while I think it will be possible to control them by
cascading shift registers, I'm worried it will be to slow.
Having more I/O pins and narrower shift registers would speed things up.
I would love to be proven wrong here, in which case I can dig out a
Pentium III with parallel port and start experimenting.
- Pontus.
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