From: James Cobb <J...@cfl.rr.com>
Subject: RE: [N8VEM-S100:1417] S-100 Bus Terminator
To: n8vem...@googlegroups.com
Date: Sunday, February 10, 2013, 8:34 PM
I agree with Jack and would want at least 2 if not 3
Jim
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Jack Rubin
Sent: Sunday, February 10, 2013 12:59 PM
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:1394] S-100 Bus Terminator
I’ve always liked the EXTERMINATOR, for the name if nothing else, but I’m not sure that combining termination with an extension card is useful. I tend to want to use an extender that won’t disturb the existing system which may or may not already have termination, and if termination is needed, then I wouldn’t want to sacrifice an extension card to provide it. I’d rather see a short board which simply provides termination in the minimal amount of space required. The CompuPro active terminator is only about 3 inches high.
Jack
Andrew:
Being a congenital penny-pincher, as well as a "tweaker", it strikes me as a lost opportunity to define a PCB like this with *lots* of unused space (and yet sucking up a full S-100 slot). At a minimum, how about filling the remaining space with a through-hole proto-area array? It would/could be accompanied by appropriate regulators along one edge but the setup/layout would be spatially similar to the buffered proto-board (replacing the buffer-area with the line-clamp area). This would leave opportunities for experimenters (with legacy S-100 backplanes) to wire-up small accessory circuits -- else no impact on the termination function?
Alternatively, place the bus-terminator circuitry onto the unused area of the bus-extender card and get three-in-one functionality with extension, termination, and probe functions. An example of this approach of combining
termination and extension was the VTE100a "EXTERMINATOR"; see:
http://maben.homeip.net/static/S100/vamp/cards/VMP%20VTE%20100-A%20Terminator.pdf
http://maben.homeip.net/static/S100/vamp/photos/VAMP%20VTE-100%20Exterminator.jpg
http://maben.homeip.net/static/S100/vamp/photos/VTE%20100a%20Exterminator.gif
If trying to go 3-in-1 ends up running into real estate issues then just combine termination & extension like the VAMP.
Another possibility would be to commit all/part of the (above) proposed proto-area to specific generally-useful functions. Two possibilities
would be a configurable basic UART serial I/O port and/or a configurable 8 or 16-bit (E)EPROM handling up to 1 MB chips. I believe that someone pointed out recently that it would be useful to have a board with these sorts of basic functions in order "bring-up" legacy CPU PCBs in a minimal configuration. One could possibly swap one of these options for the probe in a 3-in-1 configuration? Unfortunately it seems to me that when including the extension-function that the resulting routing problems when adding something like I/O or ROM might require a lot of accessory over-board wires to effectively provide a (minimal) third connection-plane. So that might not be a good idea. But the VAMP illustrates that termination+extension go together quite well.
My preference would be to leave the existing probe+extension PCB alone, and instead look towards combining termination, Serial I/O, and (E)EPROM into a single card.
This plus legacy CPU and RAM cards would result in a functional system on any "naked backplane". If some RAM could be squeezed into this multi-purpose board, so much the better :->. We have all of these circuits in tested-form, the only issue would seem to be routing. This sort of board would also be useful to a wider audience who could only populate the subsections of immediate need (e.g., not actually use the termination section if employing a self-terminated backplane) -- and this would increase the board-orders and therefore the likelihood that we'll quickly reach a good ROI threshold.
The bottom line for me is that a pure termination PCB seems like a lost opportunity. And might not easily reach critical-mass for a board-order :-<.
Attached are the schematic and PCB layout files for the S-100 Bus Terminator.
Please review and send any changes and/or corrections to me.
Thanks and have a nice day!
Andrew Lynch
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