About September of last year Andrew and I put together an S100 bus Master/Slave 80286 CPU board. This board was designed to allow one to run CPM86 and MSDOS in the S-100 bus.
As we started to consider and plan for future CPU’s for the bus and software/hardware to run with them, it became clear that it would be nice to have the capability with CPU’s in slave mode to transfer control down one more level. This would allow you to run a slave with for example a DMA controller, or temporally pass control to another CPU without going up a level and program the bus master to take care of things. Particularly because in almost all cases the bus master would be a slow 64K Z80 CPU.
The approach used was to simply duplicate the IEEE-696 protocol again using two unassigned S100 lines (NDEF1 & NDEF3). Keeping the same handshaking protocols etc. We implemented this with our 80286 master/slave CPU board here and are calling this the V2-80286 CPU board.
A brief description of this V2 board can be found here:-
http://s100computers.com/My%20System%20Pages/80286%20Board/80286%20CPU%20Board.htm#V2-80286
(Bottom of the page).
This is probably the most complex board we have done to date, definitely not for everybody! It should not be attempted by somebody starting off with these types of boards.
I will now go ahead and get a few (3 or 4) commercial quality boards made for my own use. If you think you are up to utilizing a board like this now, or in the future, let Andrew or I know so we can include you in the early “first batch”. Otherwise stay tuned for a later group purchase by (hopefully) a group member that will organize a larger purchase - at a lower price.
Note, if you already have the original V1 80286 board, all the chips on that board can be transferred to this new board.
BTW, all our planned future 16 and 32 bit CPU’s will incorporate this new circuit/protocol.