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Re: [N8VEM-S100:1374] S-100 Bus Terminator
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- Subject: Re: [N8VEM-S100:1374] S-100 Bus Terminator
- From: Paul Birkel <pbi...@gmail.com>
- Date: Sun, 10 Feb 2013 03:37:50 -0500
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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:
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 :-<.
On Sat, Feb 9, 2013 at 9:19 PM, Andrew Lynch <LYN...@yahoo.com>
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!
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