[vcf-midatlantic] 8-bit ISA slot Single Board Computer

Herb Johnson hjohnson at retrotechnology.info
Tue Sep 20 14:00:37 EDT 2016

Joseph Oprysko posted:

> Is anyone here aware of such a beast?  I have a Heathkit/Zenith Z-150
> system. It's motherboard is literally just an 8-Bit ISA backplane, the
> computer occupies 4 of the ISA slots.

I have Z-150 and related documentation. Zenith/Heath produced a number 
of models of ISA computers which used passive backplanes and several ISA 
boards to complete the PC-nearly-compatible computer. Other Zenith 
products used IBM-type motherboards with most of the PC functions on 
that board.


> I'm curious if there exists a Single Board Computer that would work in the
> 8-bit slots.
> What I would actually like to try is to have multiple SBC's on the ISA bus,
> and have them communicate with each other.

There may be single-board PC's which fit a single 8-bit ISA slot. But 
many were 16-bit ISA, the longer slot. And the PC-104 stackable bus 
standard, is essentially the ISA bus on a different connector. YOu can 
look up PC-104 if that's not familiar.

Running multiple ISA-bus "masters" on one ISA bus, may be a problem. 
Briefly: they each expect to drive the bus as a single master. There may 
be products that can share the bus with each other.

(shrug) you'll have to do some homework to become familiar with such 
things; and then of course find now-vintage products which will share 
the bus; and of course determine how to set them up, boot up sequences, 
who is in charge when, and so on.

Likely more common, are slave CPU boards, where a task or a user gets a 
CPU on a board with memory and I/O; but uses the bus to share resources 
like hard drives. this was common in S-100 TurboDOS systems. Some of the 
S-100 "IEEE-696" CPU boards, can release the bus to another CPU or DMA 
bus-master; some of those boards are fairly functional "computers". 
Multibus did this too.

But I'm guessing the idea, is to use IBM-PC ISA-class products, to check 
out multiple bus-masters and multiple CPU's, in a vintage way. a 
modified ISA backplane, may be such a way. A custom backplane may be 
able to adapt ISA "no share" bus masters to access common ISA bus 
devices. But you might look at PC-104; they are smaller cards, more 
integrated and so with more features; and they may have a multi-master 
standard as part of PC-104. And of course, they are vintage now. ;)

Herb JOhnson

Herbert R. Johnson,  New Jersey USA
http://www.retrotechnology.com OR .net

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