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BookWorm
December 6th, 2009, 10:00 PM
My NorthStar Horizon has 12 slots. A complete 256 color Microangelo system takes 9, 10 if the "genlock" (what is a "genlock"?) also takes a slot. I think it supports up to 8 CPU boards. Then there's the FPU, floppy controller, hard drive controller, tape backup controller, 6 or 8 RAM boards, a Cromemco 8PIO, a clock, Screensplitter video board, A/D board, sound board(s), cassette, video digitizer...

Maybe I should quit while I'm only up to 38 slots.

I don't want to replace the motherboard. I want to keep it original. Has anyone here ever connected a second motherboard, using heavily shielded and buffered cables, to an S-100 system with limited slots?

Oh yeah, the interface board in each box would take another slot.:wow:

monahan_z
December 7th, 2009, 12:24 AM
I doubt you could get past 2-3 MHZ with that arrangement. May want to consider boards with multiple functions.

BookWorm
December 7th, 2009, 08:01 AM
Ever heard of a "slot box" for a pee sea? If they can do it, so can we.

First, I will probably have to build the board myself. I would put buffers at each end of every signal. I would use the kind of ribbon cable with the shield on one side, like an Apple disk drive cable. Every other wire would be a ground. I've seen ribbon cables with shielding around them and insulation over that.

It still might not work. But if I can add slots to my pee sea, Why can't I add them to my S-100 system?

NobodyIsHere
December 7th, 2009, 09:38 AM
Hi! Bus length, termination, cross talk, reflections, signal propagation delays, voltage drop, floating grounds, etc. There are many reasons but John is correct. Large S-100 bus motherboards/chassis generally have problems with signal quality.

The PC expansion slot took a <5 MHz bus with 5 or 8 slots and expanded it with 5 or 8 more. Total slot count is between 10 to 16. Typically slow IO boards went in the expansion chassis like serial or parallel ports not memory or video boards. That is a much more forgiving situation than trying to add another general purpose 12-24 S-100 slots to a NS Horizon S-100 bus.

S-100 bus termination and careful design can limit the problems but not make them go away altogether. Many of the large format S-100 chassis had a lot of slots but often many slots were left empty for cooling, etc. Completely full large S-100 bus system (>12 slots) are pretty unusual and tricky to get working reliably. Adding an expansion chassis to that would be extremely difficult.

I'm not saying it is impossible but nearly so -- I would love to see it happen. IMO, the practical limit is about a dozen slots (what's available in a NS Horizon). There are exceptions but not very common.

Thanks and have a nice day!

Andrew Lynch

MikeS
December 7th, 2009, 10:05 AM
<snip>
I'm not saying it is impossible but nearly so -- I would love to see it happen. IMO, the practical limit is about a dozen slots (what's available in a NS Horizon). There are exceptions but not very common.

Thanks and have a nice day!

Andrew Lynch
Most Cromemco systems had 22 slots; a multi-user configuration could indeed fill most of those, especially if you used small memory cards and I/O cards with few ports.

But I'd agree that an external bus extender would be a bit of a challenge to keep clean, considering that even some ordinary single small-count backplanes had problems with noise once they were heavily loaded (not to mention that you're going to need some serious power and cooling).

But hey, more power to ya; Andrew, don't you have some backplanes to sell?

Chuck(G)
December 7th, 2009, 10:28 AM
22 S-100 slots, given the uneven quality of third-party boards would be impossible in a mixed-board system. It's conceivable that a single vendor's boards (i.e. Cromemco) might be made to work in such a system. But most vendors didn't pay too much attention to bus loading and capacitance that tends to many-card backplanes.

You could bridge two backplanes using some transcievers and latches, synchronized to the bus, but it would cost you at least one wait state.

NobodyIsHere
December 7th, 2009, 12:44 PM
Hi Mike! I designed a small actively terminated S-100 backplane PCB for benchtop repair/debugging of S-100 boards. Its not really intended for building a full blown S-100 system although you could use it if you wanted.

The N8VEM S-100 backplane PCB supports 6 slots. I kept it small to fit on the benchtop and also to minimize noise issues. That being said, S-100 systems are notorious for noisy backplanes.

Thanks and have a nice day!

Andrew Lynch

MikeS
December 7th, 2009, 01:08 PM
Never had any bus problems with the Cromemco systems, but the quality (and price) was a little higher than most of the other S-100 stuff, and yes, they were all exclusively populated with Cromemco cards; for some of the high-speed stuff they used a secondary bus across the opposite card edge using ribbon cable and headers.

@Andrew:
Just thought the OP might be interested in one of your boards (if there are any left); might be just the thing for this kind of experiment.

BookWorm
December 7th, 2009, 04:47 PM
Ok, maybe I should limit it to one or two CPU's, and limit the Microangelo system to 16 colors. The Cromemco 8PIO is a permanent part of the system - it controls a "switch register" (wannabe front panel) installed in the front of the computer. I will probably remove the Screensplitter. So except for the 8PIO, all boards will be NorthStar or Microangelo. Did NS ever make a Z80 equivalent of their 8088 Single Slot Computer?

What about one of those backplanes like the Archive or SOL-20 used? It would fit in the back slot, but the cables would get a little crowded.