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RE: [N8VEM-S100:1961] S-100 80386 board and RAM board availability

Thanks for feedback Antony.  It turns out the ISA-S100 converter board and the corresponding PC style VGA boards have turned out to be vastly more complicated than I anticipated.  Andrew probably has a better count, but I think we must have done 6 prototypes so far.   It’s a very long story as to the problem(s). It has to do with the fact that VGA board chips require their initialization RAM and Ports to be in 8 bit bytes. They cannot initially accept 16 bit data.  So for our 8088 CPU board absolutely no problems. Any VGA, EPA, CGA board I use works 100% fine.


For 16 bit CPU’s one must send initially two 8 bit bytes back to back with a complete ISA MEMW* etc signal. Likewise for reads.  Even this I solved and can write to at video boards UNTIL an 8086 “rep” code prefix is used. (Screen clear, move etc).  During these times the boards jam IO_BUSY signals on the ISA bus for extra time.   The problem is the S100 bus is already held in a wait state during the back to back read/writes.    All this is done by careful use of a shift register pulling off different signals.  The problem is the ISA wait requests crap up the sequencer. They are variable in length and can strike any time.  Worse I have to make sure runt clock signals are not spliced together.  Probably way much info than you wanted.


Anyway I think the solution is to use two shift registers, the first triggering the second when it is done.  Unfortunately all this has soaked up literally 100’s of hours. (Perhaps I’m a slower learner)!


With Andrew we have now decide to shelve this project for a few weeks and get back to the backlog of other boards.

Just got the latest 80386 prototype going here (V6). Runs with a 40MH clock on the 32 bit overhead bus (10 MHz. for S-100 RAM/IO).  Waiting for SRAM chips to build a 32MB S100 daughter board, (8MB working fine).


However the elephant in the room is the need for a DRAM daughter board (as well as a future 80486 board).   In spite of some early interest nobody has come up with a suggested design.


By comparison the SMB, DMA (will be part on a new MSDOS support board), and a few other repeats should not take too much time. 

Please try and hang in there I will up the turnover ASAP.







John Monahan Ph.D

e-mail: mon...@vitasoft.org

Text:    mon...@txt.att.net



From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Ants Pants
Sent: Thursday, October 10, 2013 2:44 PM
To: n8vem...@googlegroups.com
Cc: mon...@vitasoft.org
Subject: Re: [N8VEM-S100:1961] S-100 80386 board and RAM board availability


Hi John,


yes i have been following your site with respect to the S-100 to ISA board. im looking forward to seeing it :-)


i almost cant wait to see a production version of the 80386 board and static ram board! is there any prototype boards i could get my sticky hands on to have a play with?? :-D .. im very keen to assist in a DRAM board with maby the full 4GB of memory on it or the possibility to add memory as one would need? maby we could use some SDRAM and have some nice connectors onboard.. that would look really smart! maby we would have to start talking about a whole new bus though.. maby an ISA or PCI bus board?.. the future of the computer project?


the MSDOS board with a DMA controller would be nice. 


an updated SMB would be nice.. i would love JAM and JUMP to be added!! (i dont even have a SMB at the moment.. isnt that sad) 





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