gbadev.org forum archive

This is a read-only mirror of the content originally found on forum.gbadev.org (now offline), salvaged from Wayback machine copies. A new forum can be found here.

Hardware > DIY GBA to TV adapter

#34792 - emumanXM - Wed Jan 26, 2005 8:33 am

Well, the GBA to TV/TV de Advance etc are all cheap chinese made junk. I really don't mind it, but for the price I paid, I expect something better. The RGB encoder has plastic over the top of the IC to hide it's part number. It's a CXA2075. It's found in older consoles like the genesis and psx. From what's said about it on the net, it's a high quality part. It produces a nice image on my sony wega. It gets extremely hot and uses a ton of power. There are two other major ICs inside, one is a CoB(glop-top), and one is some sort of IC made by Q-MARK. One must be a D/A converter, I'm not sure what the other one is. It could be a framebuffer or might be some sort of RAM. Rest of the ICs are standard logic and regulators. The CoB IC has an equivelant TQFP100 package.

I want to use a video DAC and make my own that uses less power and requires less circuitry. Texas Instratments has a 10 bit RGB DAC. Can output component, S-Video, and composite video according to it's datasheet. It can be found here: http://focus.ti.com/lit/ds/symlink/ths8133b.pdf
but I'm not sure how well it will work for this application. I'd like to use high resolution displays like VGA and HDTV as well as S-video, etc, but I want to keep the design as simple as possible. Anyone have any suggestions on what to use?

Thanks.

#34819 - Cyberman - Wed Jan 26, 2005 6:24 pm

look At conexant's CX25870/871 just to warn you it can give you a headache if you stare at it too long LOL.
You may need a chip for scaling the video output of the GBA, that might make things a bit of a pain.

Cyb
_________________
If at first you don't succeed parachuting is NOT for you.

#34823 - emumanXM - Wed Jan 26, 2005 7:10 pm

The THS8133 does not require a microcontroller, the one from conexant does. Plus TI will send me a free sample :P Why would I need to scale the output? It should fit on an NTSC display. But I never attempted such a project before, so please give me your input. :)

#34824 - tepples - Wed Jan 26, 2005 7:17 pm

emumanXM wrote:
Why would I need to scale the output? It should fit on an NTSC display.

It depends. For one thing, the vertical scan rate, horizontal scan rate, and pixel clock rate of the GBA display don't match those of NTSC television, so you'll need to use a full 75 KiB frame buffer for a good picture. For another, TV resolution is 352x240 non-square pixels, and if your TV encoder doesn't support a square-pixel input mode, you may need to stretch the 240x160 pixel output of the GBA by a factor of 1.1 horizontally (to 264x160) to keep squares square and circles round.
_________________
-- Where is he?
-- Who?
-- You know, the human.
-- I think he moved to Tilwick.

#34856 - emumanXM - Thu Jan 27, 2005 6:51 am

tepples,

With the right clocks, and the data clock output from the LCD, ignoring the gba's H and V sync, can I do it? I wonder if the TV de Advance uses a framebuffer...

#34857 - tepples - Thu Jan 27, 2005 7:27 am

You can make a display out of the GBA without a frame buffer; it just won't be compatible with any television set. The GBA's horizontal scan rate is 13.6 kHz, which NTSC and PAL televisions cannot sync to, being designed for horizontal rates more in the neighborhood of 15.7 kHz. Trust me; you'll need to watch at least the GBA's pixel clock and vsync, timing framebuffer writes off those.
_________________
-- Where is he?
-- Who?
-- You know, the human.
-- I think he moved to Tilwick.

#34928 - emumanXM - Fri Jan 28, 2005 7:56 am

The GBA Transverter uses the same circuitry as the one made by Q-Mark, but they use ICs actually in a package. I really want to get one so I can see how these guys did the frame buffer.