Updated to 3 Todd John
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Todd Goodman Sent: Monday, February 9, 2015 1:36 PM To: [email protected] Subject: Re: [N8VEM-S100:6251] Re: A S100 Bus (8 bit data bus) XVGA Video Display board I'd like three if it's not too late. Thanks, Todd On Mon, Feb 9, 2015 at 3:22 PM, monahanz <[email protected]> wrote: > OK I have the following list for people that would like an S100 VGA > video > board:- > > Fabio,3 > David ,2 > Todd,1 > Matt,1 > Andrew L., 1 > Neil,1 > Peter,1 > Elsid, 1 > Paul B., 1 > Gary, 1 > Peter Cole, 1 > John M.,4 > > So I will order 20 boards (2 extra). Will take 3-4 weeks. > Do NOT send any PP payments until you receive the boards. > Peter could you send me your shipping address. > > John > > > > > On Wednesday, February 4, 2015 at 11:45:09 PM UTC-8, monahanz wrote: >> >> Well here it is after no less than 10 prototypes I'm delighted to >> introduce the first XVGA video board that sits in the S100 bus. See >> here:- >> http://s100computers.com/My%20System%20Pages/VGA%20Board/VGA%20Board. >> htm >> Scroll half way down the page. >> There is one major limitation with this S100 bus XVGA board, It will >> only work with our 8088 CPU board. With that board as best I can tell >> it is rock solid running MSDOS with an S100 bus clock speed (PHI) of >> 8 MHz (i.e. a 24 MHz Oscillator on the board). It will NOT work with >> our current 16 bit CPU's ( the 8086, 80286 or 80386). The reason for >> this is due to the fact that these VGA chips (at least for the Cirrus & >> Trident chips), require the >> CPU to be able to send 16 bit data as two back to back 8 bit bytes. The >> chips actually have dedicated lines (MCS16* & IOCS16*) to flag the >> CPU to let it know it is capable of a 16 bit transfer. However I >> found out the hard way, that these chips do not always exercise this >> option -- particular during initialization. On our ISA converter >> board I played around with the circuit to sequentially send two 8 bit >> bytes using Sergey's ISA Super VGA board. I could not find a >> reliable solution. The best effects were sensitive to the bus CPU speed and >> failed altogether at high MHz speeds. >> >> The fundamental problem was that these VGA chips can and do pull wait >> states on the bus at impossible to determine times (particularly during >> screen scrolls). The length of the wait states is highly variable. I >> concluded the only way to solve this is to redo the S100 CPU boards >> themselves so that if the 16 bit CPU board does not get a SIXTN* >> acknowledge from a sXTRQ* it proceeds to send two back to back 8 bit bytes. >> This was actually part of the IEEE-696 specification. However most >> manufactures at the time (an also in our cases), ignored this and >> simply supplied 16 bit capable RAM and/or IO boards. The only >> documented circuit I could find was the (excellent) one described for the >> TecMar 8086 board. >> >> The good news is that the 80486 CPU has the ability to on the fly >> send 8, >> 16 or 32 bit data depending on the chips on the receiving end. The >> other good news is that this XVGA board can send and receive 16 bit >> data. The chips themselves have 16 bit data pins so such a board >> should work at full speed with such a CPU. Most of the time >> transfers will be 16 bits but initialization and ROM access will be 8 bits >> -- just as in the IBM-AT box! >> >> I must point out however that currently this is all theoretical. I am >> in the process of building a knockout 80486 CPU board that should in >> theory be capable of working with any S100 board (old or new). If >> this does not come about then I would fall back to modifying some of our >> earliest CPU boards. >> - That's the plan. >> Anyway wanted to let the group know of the board. I will be doing a >> usual group order of bare boards in the next week or so. If >> interested please let me know. >> > -- > You received this message because you are subscribed to the Google > Groups "N8VEM-S100" group. > To unsubscribe from this group and stop receiving emails from it, send > an email to [email protected]. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
