RE: [N8VEM-S100:763] S100 VDP success

["Andrew Lynch" <LYN...@YAHOO.COM>]

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&param=ECB%20N8%20prev
iously%20known%20as%20the%20Home%20Computer

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&param=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