Hi John, I'd like three please.
Thanks! Todd * monahanz <[email protected]> [150205 02:45]: > 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* > <file:///C:/Users/John%20Monahan/Documents/My%20Web%20Sites/S100Computers/My%20System%20Pages/8088%20Board/8088%20CPU%20Board.htm>. > > 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* > <file:///C:/Users/John%20Monahan/Documents/My%20Web%20Sites/S100Computers/My%20System%20Pages/8086%20Board/8086%20CPU%20Board.htm>, > > *80286* > <file:///C:/Users/John%20Monahan/Documents/My%20Web%20Sites/S100Computers/My%20System%20Pages/80286%20Board/80286%20CPU%20Board.htm> > > or *80386* > <file:///C:/Users/John%20Monahan/Documents/My%20Web%20Sites/S100Computers/My%20System%20Pages/80386%20Board/80386%20CPU%20Board.htm>). > > 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* > <http://www.malinov.com/Home/sergeys-projects/isa-supervga>. 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* > <http://s100computers.com/Hardware%20Folder/TecMar/8086%20Board/8086%20Board.htm>. > > > > 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.
