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RE: [N8VEM-S100:6265] Re: A S100 Bus (8 bit data bus) XVGA Video Display board
OK have you down Robert
-----Original Message-----
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Robert Greenstreet
Sent: Monday, February 9, 2015 6:01 PM
To: n8vem...@googlegroups.com
Subject: Re: [N8VEM-S100:6265] Re: A S100 Bus (8 bit data bus) XVGA Video Display board
Hi John,
If possible, please put me down for 1ea. XVGA Video Display board.
Thank you,
Robert Greenstreet
> ----------------------------------------------------------------------
> --
>
> Date: Mon, 9 Feb 2015 12:22:53 -0800
> From: mon...@vitasoft.org <mailto:mon...@vitasoft.org>
> To: n8vem...@googlegroups.com <mailto:n8vem...@googlegroups.com>
> Subject: [N8VEM-S100:6247] Re: A S100 Bus (8 bit data bus) XVGA Video
> Display board
>
> 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.h
> tm
>
> 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
> <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.
>
>
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