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Re: S100 VDP success
Hi Leon,
Thanks! Good news on the AY-3-8910 chips!
Regarding the VGA interface, on the ECB side there was a recent board
called the "Color VDU" which introduced a circuit that converted RGBi
signals to VGA although it kept the sync at15+ KHz
Some modern LCD VGA monitors share circuitry with similar TVs and are
able to sync at much lower frequencies than most CRT VGA monitors are
able to. The circuit was surprisingly simple.
Unfortunately I don't have a sync doubler circuit and think it would
be rather difficult to make one.
I am very glad to see movement on the S-100 VDP project. This has a
lot of potential for a really neat board.
Thanks and have a nice day!
Andrew Lynch
On Mar 26, 5:41 am, Elsid <le...@swiftdsl.com.au> wrote:
> Hi Andrew,
>
> Yes, I would like to build a sound generator on this board. I bought couple
> of AY-3-8910s 30 years ago on sale. I knew they'd come in handy for
> something someday.
> Do you have a circuit in mind for the VGA output for the VDP board? Would
> it have a sync doubler or would it only be able to drive VGA monitors that
> sync down to 15.57kHz?
>
> Best regards
> Leon Byles
>
>
>
> On Monday, 26 March 2012 04:16:53 UTC+11, lynchaj wrote:
> > Hi Leon! Thanks! Wow! That's fantastic news! Woo Hoo!
>
> > Sorry for the late reply. Frankly I think I've forgotten who is even
> > working on the S-100 VDP but I *think* it is yourself, Neil, and Dave.
> > That
> > makes sense since I still have two of the five prototype boards left. If
> > I've missed anyone I apologize. My mind has been elsewhere for the last
> > three months it seems...
>
> > I will make the corrections on the S-100 VDP board. This has a lot of
> > potential to be a really neat project. Having a working demonstration
> > really helps as well. Are you interested in building up a AY-3-8910 sound
> > generator chip circuit? I think that this board with a V9938 and an
> > AY-3-8910 would have a reasonable chance of some amount of MSX
> > compatibility.
>
> > We can clone the AY-3-8910 and joystick ports from the N8 design and make
> > adjustments to the IO decode logic.
>
> >http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder¶m=ECB%20N8%20prev
> > iously%20known%20as%20the%20Home%20Computer<http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder¶m=ECB%20N8...>
>
> > Would the rest of the S-100 VDP team please give a quick update as to where
> > you are with the project?
>
> > Thanks and have a nice day!
>
> > Andrew Lynch
>
> > > -----Original Message-----
> > > From: n8vem...@googlegroups.com [mailto:n8vem-
> > > s1...@googlegroups.com] On Behalf Of Elsid
> > > Sent: Monday, March 19, 2012 7:57 PM
> > > To: N8VEM-S100
> > > Subject: [N8VEM-S100:763] S100 VDP success
>
> > > I've finally had some success getting video out of the prototype S100-
> > VDP
> > > board.
>
> > > The first thing I found was the data bus on the V9938 swapped around.
> > > That is, D7 was wired to CD0 not CD7, D6 was wired to CD1 not CD6 etc
> > down
> > > to D0. I think this may have been an early error on one of the prototype
> > > N8VEM VDU boards also.
>
> > > I correct the Data bus swap around but still no video output on p21
> > > COMP_VIDEO or P22,23or 24 (RGB). I should say there was actually a
> > > composite video signal complete with color burst and synchs but there was
> > > no video component on the top half of the waveform. I tried another V9938
> > > - same result. I pulled out the BT478 to just try and get the V9938 part
> > going
> > > on its own. Still no luck.
>
> > > Finally last night Wayne posted that he'd found some problems were caused
> > > on the N8VEM Color VDU board when the VT82C42 is not reset. I looked at
> > > the VDP reset circuit and found that the V9938 is not receiving a reset
> > > because BRD-RESET* is being gated by SYNTMS* at U27C. SYNTMS* is reset
> > > at turn on by BRD-RESET*. - Thanks for the inspiration Wayne.
>
> > > I'm not sure what the function of SYNTMS* is. If it's to enable a
> > > programmable reset for the V9938 we may be better off inverting it and
> > > eliminating the inverter U11F after U27C. This should give us a reset
> > from
> > > either SYNTMS or BRD-RESET.
>
> > > I was using a modified version of HW9918.COM to test the VDP board so I
> > > added a couple of lines to toggle the SYNTMS* signal to reset the
> > > V9938 in the initialization section and Bingo - "Hello World" popped up
> > on
> > the
> > > screen.
> > > I've put some photos and the test program on the N8VEM site at:
> > >http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder¶m=VDP<http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder¶m=VDP>
> > > for anyone who is interested.
> > > I set the address base to 90H but maybe it would be nice to change this
> > to
> > > 98H (start of the V9938 registers) for MSX2 compatibility. I think it
> > will
> > need
> > > some rewiring in the address decoding.
>
> > > Next step is checking out the BT478 and maybe VGA output.
>
> > > How's everyone else going with their VDPs
>
> > > Leon Byles- Hide quoted text -
>
> - Show quoted text -