News:

NEW GAME: Jack and the Beanstalk ! Check this topic!

Main Menu

Philips Videopac + G7400

Started by kcmunchkin83, July 20, 2012, 11:05:10 PM

Previous topic - Next topic

ccc---

I am very happy owner of two G7400s with working power buttons  :)

kcmunchkin83

I didn't realize they were so common and not that expensive. Thank you for letting me know and for the appropriate eBay links where I can look for one. Who knows maybe I'll add one to my collection one day.  :) Any ideas how to make it work in the US?

VideopacBelgium

I'm working to build a JOPAC with SGVA output. Maybe you'll be interested.
Videopac digger

Rene_G7400


gertk

Quote from: VideopacBelgium on July 26, 2012, 09:13:20 PM
I'm working to build a JOPAC with SGVA output. Maybe you'll be interested.

What kind of electronics are you using for this, I assume you are making a scanline doubler ?

From my VGA LCD screen project the biggest problem was creating a new Hsync signal at double the frequency of the normal Hsync.
I used a GAL chip to create a 113 (114) counter but found out later that the VDC is not completely in sync: Quote from kevtris "There's 227.5 cycles per scanline" which explains the random jitter effects on the VDC output (hardly noticable)
The plus graphics part runs cycle perfect. For buffering a complete line I used a TMS4C1050 VRAM chip, it is a 4 bit chip, perfect for the Videopac RGBI system.
>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<

Rene_G7400

Quote from: gertk on July 31, 2012, 12:59:00 PM
"There's 227.5 cycles per scanline"

This is only true for NTSC consoles (VDC 8244), for PAL consoles (VDC 8245) there are 228 VDC cycles (pixels) per scanline.

gertk

Quote from: Rene_G7400 on July 31, 2012, 11:39:31 PM
This is only true for NTSC consoles (VDC 8244), for PAL consoles (VDC 8245) there are 228 VDC cycles (pixels) per scanline.

Then it should be possible to sample the VDC output 'spot on', just need to know on what clock edge the video data from the VDC is stable. I will have to fire up the oscilloscope to check. Maybe I need a latch instead of a buffer in front of the inputs of the VRAM chip. As i said the output of the plus part is captured perfectly, just the VDC output drifts a bit.
 
>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<