Re: Help with S-100 VDP board VGA output

[lynchaj <lyn...@yahoo.com>]

Hi, it is possible that if CSYNC* = HSYNC* AND VSYNC* then VSYNC* =
CSYNC* XNOR HSYNC*

Leon, would you please confirm that CSYNC* and HSYNC* pins on the
V9938 are TTL level outputs?

If they are TTL outputs and you happen to have 74LS86 XOR and 74LS04
inverter chips available would you please test to see if we can
reconstitute VSYNC* signal?

Thanks and have a nice day!

Andrew Lynch

On Apr 1, 8:41 pm, "Andrew Lynch" <LYN...@YAHOO.COM> 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
>
>  Printing S100_VDP-sch.pdf
> 356KViewDownload