VGA RGB palette conversion? - Page 1
Forum section: electronics / projects

author: algorithm
author_rank: Regular Contributor
timestamp: December 01, 2016, 12:32:52 am
content: What Im working with has an LCD display with 4 data lines coming out of a VDP (video display processor)I am trying to find out a way to use the RGB signal from those 4 lines. I saw this,Would something like this work? Does anybody have any better ideas?I considered using a different VDP with RGB output pins to intercept those data lines, and ideally display from the RGB pins. Although that thought was a shot in the dark, and I had no idea if something like that would work or not.Any advice is appreciated,Thanks

author: moffy
author_rank: Super Contributor
timestamp: December 01, 2016, 12:52:26 am
content: So you are using the resistors as a crude DAC? If so you are going to run into bandwidth problems. The sync and intensity signals need synchronisation, it will be moderately tricky. What bandwidth/resolution are you looking at?

author: amyk
author_rank: Super Contributor
timestamp: December 01, 2016, 03:47:15 am
content: If the timing is vaguely VGA-compatible any modern monitor should be able to sync to it. Depending on how much current that VDP can source, a resistor DAC could be OK, or you may want to add a buffer amp to drive it.

author: algorithm
author_rank: Regular Contributor
timestamp: December 02, 2016, 03:11:14 am
content: Quote from: moffy on December 01, 2016, 12:52:26 amI honestly have no idea what Im doing as of yet.Well with the sync there are pins for vertical sync(vsync), horizontal sync(hsync), and composite sync (csync).I just wish I could get direct R, G and B lines out of the thing without having to make an ulterior circuit.Quote from: amyk on December 01, 2016, 03:47:15 amWell thats what I was thinking, if I could just get RGB I could wire a VGA HD-15 directly to it. (of course Im not so knowledgable with such things)The screen is 12-bit RGB. "only the upper 4 bits of each are used (12 bits total) ""you would need 3x 4 bit A to D converter chips and a way to split into RGB video"There is this, but I really wish there was a more direct way to get RGB.FWIW I dont mind if the resolution is smaller.Part of me figures if there was a better way someone would have done it, but I also have a feeling there is a way...Once again thanks everyone.

author: Someone
author_rank: Super Contributor
timestamp: December 02, 2016, 03:36:40 am
content: Quote from: algorithm on December 02, 2016, 03:11:14 amYou've really poorly described a) what you're doing, and b) what you want to achieve.For everyone else, this is un multiplexing the RGB signals going to an LCD in the Sega Game Gear:http://www.freewebs.com/vgmods/gamegearmodifications.htmThe circuit could be made smaller with a CPLD but it still won't be simpler. If you have problems getting the image to work try a modern LCD monitor with RGB (VGA) inputs since they will sync to almost any signal.

author: hamster_nz
author_rank: Super Contributor
timestamp: December 02, 2016, 05:19:15 am
content: Have a look at the schematics of any FPGA dev board with RGB out. This arrangement is pretty common and works fine.