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Re: An 80386 CPU and RAM board for tthe S-100 Bus

Thanks John for the update!

Andrew Lynch

On Monday, April 15, 2013 10:52:34 PM UTC-4, monahanz wrote:

I would like to mention that Andrew Lynch and I have just completed work on the final prototype (V4!) of a new 80386 Master/Slave CPU S-100 bus board. This board is capable of reaching up to36MHz for its clock input when used with RAM on its daughter board (see below). 

For those that have been following progress this has been a long project.  It utilizes the 16 bit mode of the 80386 to address up to the 16MG of RAM the S-100 bus is capable of addressing. A second daughter board system with two overhead ribbon cable connectors is utilized to allow 32 bit addressing to one or more RAM boards. This "32-Bit S-100 Overhead Bus" as I call it, allows the CPU to run at its maximum speed (no wait states) and with the current static RAM chips in pipeline mode.  The current daughter RAM board utilizes 16MG of static RAM. The plan is to next add high capacity DRAM boards.

It turned out that the 80386 splices very nicely into the S-100 bus. The CPU control signals are clean and tolerant.  In fact the interface is simplifier than our earlier 8086 and 80286 boards. No bus controller or clock generator chips for example are needed.

The real fun in working with this chip is now one can take advantage of the 32 bit programming mode of the 80386 and its vast memory addressing capability.  It took some time to understand how to switch the CPU into “protected mode” and I have written this up to make it easier who may like to start into this world for the first time.

For those with S100 systems that would like to get into 32 bit system hardware and software this board may be a great place to start.  In the next few weeks we will be sending an order in for a production run of both bare boards.   In all lightly-hood this will be a onetime batch/order, so if you think you would like to play around with a board like this in the future, now is the time to order a board.  Also I should point out, this board is fairly sophisticated, I would not recommend it for people starting off with S100 boards. They should “cut their teeth” on say the 8088 CPU board first.

For more information about both boards please see here:-


For information about 80386 Monitor software please see here:-