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Prototype S100 Boards for 80386 CPU with 8 or 32MB Static RAM

monahan_z

Experienced Member
Joined
Oct 19, 2008
Messages
260
Location
San Ramon, CA
Just an update for those following these new S100 boards Andrew (at N8VEM), others and I (at S100Computers.com) have been constructing.

I have just finished initial tests of three new prototype boards
An 80386 CPU master/slave CPU board.
an 8 MB Static RAM board
and a 32MB static RAM board.

The RAM boards are connected to the CPU board via an "32-Bit S-100 Overhead Bus"

The 80386 runs at 8 MHZ for the up to 16MG or RAM on the S100 bus. It switches (on the fly) to 32 MHz for the above RAM boards (no wait states). For these two boards the CPU can run in "pipeline mode". A 80386 monitor with real and protected mode functions/test is provided. The board runs standard MS-DOS (v4.01) with this monitor.
See here for more information:-

http://www.s100computers.com/My System Pages/80386 Board/80386 CPU Board.htm

http://www.s100computers.com/My System Pages/80386 - 8MG RAM Board/8MG Static RAM Board.htm

http://www.s100computers.com/My System Pages/80386 - 32MG RAM Board/32MG Static RAM Board.htm

This is a rather complicated setup and definitely not for beginners. We will soon be putting together a batch order for a “production run of bare boards”. Keep an eye out for the announcement. Regular users know these batches do not come around often.
 

rorypoole

Veteran Member
Joined
Dec 8, 2004
Messages
585
Location
UK, Surrey
I have looked at your S-100 expandable 386DX card and it is a bit of inspiring design!! switching the clock speed and bus width when needed and external 32bit access to the ram cards is very very clever.

I had found out about the bus size control pin on the 386dx years ago BS16, but there is also the BS8 pin used to set the bus to 8 bit? the 486 and I think Pentium overdrive chips (built to upgrade 486 motherboards) have the same BS8 bus size pin, and there is A20M pin that sets the memory address to 1mb!
when I was at college I was thinking of building an adapter so I could use a 486 or Pentium overdrive chip in my IBM XT! with maybe some more ram, I did not build it as I lacked the electronics knowledge, but could the same idea be used to put a Pentium overdrive chip or 486 in an S-100 bus computer?
you would have to buffer the cpu so you could run is at a much faster than a few mhz the S-100 bus and other cards can do.
dose the BS8 pin work how I think it dose?

it would be cool to be able to add one or more 486 or Pentium overdrive cpu cards to an existing 8 bit S-100 computer and having it work with all the original 8 bit cards including the old 8080 or z80 cpu card!

a striped down version of your 386 S-bus cpu card could probably work with a 486 in 8 bit mode, but an internally clock tripled 486dx4 in a 2mhz S-bus computer it would run at 6mhz but 12mhz bus speed would give you a 36mhz 486, how far can you underclock it?

it looks like the Pentium Overdrive will underclock to 8 MHz and maybe lower!
www.winhistory.de/more/386/xpmini.htm.en


good luck with the 386 S-100 bus card, I am looking forward to reading about the larger ram cards!
 
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rorypoole

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Joined
Dec 8, 2004
Messages
585
Location
UK, Surrey
it looks like others have had the same idea

Building a 80486 S-100 Bus CPU board.
http://www.edaboard.com/thread303338.html

Layout for a 80486 CPU Board
www.s100computers.com/discus/messages/3/37075.html?1384619816

Embedded Intel486™ Processor
Hardware Reference Manual
www.pld.ttu.ee/~prj/486dev.pdf

I have found 486 upgrade chips rated at 133mhz but can be overclocked to 150mhz, that would be good to but in a S-100 bus computer! would still need a cpu multiplier and voltage regulator adapter circuit
 
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rorypoole

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Joined
Dec 8, 2004
Messages
585
Location
UK, Surrey
I have found the Powerleap PL-K6-III, socket adapter it takes a 333mhz to 600mhz AMD K6-III L1-Cache: 32 + 32 KiB (Data + Instructions)
L2-Cache: 256 KiB, fullspeed

>This upgrade is designed specifically to upgrade Socket 5-7 systems to the K6-III CPU. The K6-3 is the fastest CPU available for Socket >7.

486 motherboard upgrade chips and adapters
www.cpushack.com/UpgradeProcessors.html

but how meny cpus have the BS16 or BS8 or equivalent pin? when the S-100 486 cpu card is working you could test some of the upgrade chips and see
 
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rorypoole

Veteran Member
Joined
Dec 8, 2004
Messages
585
Location
UK, Surrey
When you say it will run up to 32 MHz, you mean it will accept a 64 MHz oscillator (CLK2=64MHz), right?

it is just a what if, I took the S-100 bus clock and multiplied by the CPU's multiplier

why would a 486 need a BS8 pin to be able to switch the data bus from 32bit to 8bit?
to use a 1980s 8 bit ISA card? if so the a feasibility study could be easly done with only an old ISA only 486 motherboard and a 8bit rs232 card in the ISA bus with some leds hooked up, so you can see if it has access to it? and a selection of 486 upgrade adapters and chips.
 
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