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Re: Help with S-100 VDP board VGA output

Hi Leon!  Thanks!  There is a mildly less terrible datasheet for the
V9958 chip with a similar diagram on page 26.


Thanks and have a nice day!

Andrew Lynch

On Apr 2, 4:32 pm, Elsid <le...@swiftdsl.com.au> wrote:
> There may be a problem with HSYNC from the V9938.
> The sync pulses are missing during the blanking period.
> The data sheet shows a negative HSYNC mode on page 131 that continues
> through the blacking period, but I can't see how to get into this mode (my
> scanned copy is to low in resolution to see the writing below the HSYNC
> label on the left of the waveform) Can anyone help?
> <https://lh6.googleusercontent.com/-QTr7zOVr40M/T3oLTzt4mMI/AAAAAAAAAA...>
> Top trace is CSYNC, bottom trace is HSYNC. Verticle scale is 2 V/Div.
> Regards
> Leon
> On Monday, 2 April 2012 10:41:16 UTC+10, lynchaj wrote:
> > Hi
> > I’ve been working to update the S-100 VDP with the AY-3-8910 sound
> > generator and convert to VGA output.
> > However, I’ve hit a major roadblock and need some help to move forward on
> > this project.
> > It turns out the V9938 does not generate a separate VSYNC signal.  It
> > generates HSYNC and a CSYNC signals separately however both CGA and VGA
> > require separate VSYNC and HSYNC signals.
> > I imagine there is some relationship between CSYNC and HSYNC where you
> > could synthesize VSYNC but after much studying the V9938 datasheet and
> > numerous Google searches I don’t know how to do it.
> > Please take a look at the V9938 datasheet and let me know if generating
> > VSYNC is possible and how to do it.  Without a separate VSYNC we lose any
> > hope of even partial VGA compatibility!
> > Thanks and have a nice day!
> > Andrew Lynch