[Simh] Hardware Requirements

Fri Dec 10 20:10:13 EST 2010

I've got a Technico 9900-based process control system arround here 
somewhere. The 9900 CRU was handy for that sort of thing - clumsy for 
more normal purposes.

I also have a a few front panel here, and believe it or not was thinking 
about using the 9900 CRU chips (which have both a 74xxx and a 99xx 
number) to drive the pannel off the parallel port. They are 8 bit, bit 
addressable latches. I would have used a parallel port. 7 of the port 
data bits would select the bit, the remaining port data bit would be the 
value. Speed would probably be good enough - parallel ports can be fast. 
You don't want an emulator that drives a front pannel to be too fast or 
the blinking ligts won't look right.

That is one project that dropped plumb off the bottom of my "someday" list.

Armistead, Jason wrote:

>Göran
>
>Given that TI obsolete the TMS9900 range of CPUs probably 20 years ago, using their 1-bit serial I/O scheme, know as Communications Register Unit (CRU), is probably not a great idea.  It never really caught on outside of TI's own product lines, and it still required (up to) 12 bits for the address bus used to select CRU bits (up to 4096 input and 4096 output bits), plus the 3 CRU signals CRUIN, CRUOUT and CRUCLK.
>
>Using a modern PC as a starting point, maybe you'd be better off with a USB-based device which writes out to a SPI-like serial bus.  Parallel ports are disappearing (and now almost totally non-existent on notebook PCs and even their docking stations), and CANbus is too specialized to each vendor (and thus difficult to find drivers for every OS, especially Unix/Linux-based ones).  Companies like FTDI have some neat USB I/O controller devices (some that are nicely programmable) and could be adapted to your needs using simple control instructions across the USB channel.
>
>Jason
>
>-----Original Message-----
>From: Göran Åhling
>Sent: Friday, 10 December 2010 3:47 PM
>To: simh at trailing-edge.com
>Subject: Re: [Simh] Hardware Requirements
>
>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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>>    
>>
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