Genesis/Mega Drive display output mod - Page 1
Forum section: electronics / general

author: Ampera
author_rank: Super Contributor
timestamp: August 03, 2017, 12:21:44 pm
content: I tend to come here for the odd retro computing problem, as the bank of knowledge here is much greater, and it's a lot nicer than joining a random forum with a random community.I have a Commodore 1084 CRT monitor. It's a great display with Chroma/Luma inputs, Composite inputs, CGA compatible RGBi inputs, and analog RGB inputs. My problem is that it's PAL.This is fine for my PAL Commodore 64, and I don't want to change the monitor to NTSC.I want to hook up a Sega Genesis, the primary reason being that my PVR2 capture device doesn't want to pass it through to HDMI (It has no problem with most other analog signals, just the Genesis)When I hook up the Genesis to my 1084, I get no colour, but the picture is is perfectly fine in standard greyscale B&W (yes, I know, oxymoronic).So I am aware the Genesis has switches/solder bridges that control the region and the video output. My issue is that I don't know if modifying my Genesis for PAL colour is going to slow down the CPU and make my NTSC games unplayable. There is no real region locking on the Sega Genesis, and I just need the PAL colour signal, scan rates don't need changing.The base question here is if I change my Genesis to output in PAL, is it going to underclock the system? If so I need to get an NTSC to PAL colour converter.

author: Halcyon
author_rank: Unknown
timestamp: August 03, 2017, 12:26:36 pm
content: NTSC to PAL (and vice versa) converters were pretty cheap (when they were popular). Many are now discontinued.Rather than modifying your console, you're probably better off getting a multi-system composite video (PAL/NTSC/SECAM) to VGA or HDMI converter.https://www.jaycar.com.au/composite-video-rca-svideo-to-vga-converter/p/XC4906I'm sure you can find similar devices for cheaper on ebay in the USA.

author: Ampera
author_rank: Super Contributor
timestamp: August 03, 2017, 12:53:21 pm
content: Then I can't use my nice 1084 display.I think when I need to use it I'll just buy a cheapie 10-20 USD PAL/NTSC converter. They even still have them on Amazon.EDIT: Also at that price I might as well just buy a composite display. (40 USD for a converter)

author: stj
author_rank: Super Contributor
timestamp: August 04, 2017, 08:50:46 pm
content: i seem to remember the megadrive has a din socket that has RGB available on it.

author: Ampera
author_rank: Super Contributor
timestamp: August 04, 2017, 09:31:09 pm
content: Quote from: stj on August 04, 2017, 08:50:46 pmIt does, but the only issue is that it's still NTSC RGB. I don't know if my PAL display will take it.Although since the colour channels are separate, and I can adjust stuff.You know if the pinout is identical, that actually might work.

author: ebastler
author_rank: Super Contributor
timestamp: August 06, 2017, 08:46:50 pm
content: Quote from: TwoOfFive on August 04, 2017, 09:31:09 pmIn their original narrow sense, PAL and NTSC refer just to the modulation schemes (i.e. how to encode color in a single composite video signal). That modulation is not used at all in RGB mode. Hence, if your monitor and the Genesis both have RGB inputs/outputs, a major part of the problem is solved.More loosely speaking, PAL and NTSC are often also used to refer to the complete set of parameters of a video standard -- frame rate, number of lines etc.. In these respect, PAL and NTSC differ as well, and that difference is of course preserved when transmitting the signal via RGB.It is certainly worth a try to connect the two systems; quite possible that the monitor can handle 60Hz frame rate as well. The pinout of the RGB connectors should be your least worry. I am sure you can Google the respective pinouts, and rig up an improvised adapter for testing. (Keep those loose wires short and you should be alright...)

author: Ampera
author_rank: Super Contributor
timestamp: August 06, 2017, 10:38:51 pm
content: Actually the problem would be the cable. I got the pinouts, but I don't have a large supply of DIN connectors and cables to wire together.

author: Ampera
author_rank: Super Contributor
timestamp: August 07, 2017, 04:11:02 pm
content: Right, so I do want to manufacture a cable. I am perfectly competent in actually constructing such a cable, I just need help with figuring out what goes where.This is the pinout for the Analog and Digital (IBM CGA compatible) RGB inputs on my monitor. I obviously need the analog one, which seem to be pretty much SCART RGB.This is the pinout for my Mega Drive/Genesis:So obviously, red goes to red, green to green, blue to blue, ground to ground. My issue is what to do with the sync.Excuse me while I get stupid here, but where does that one go? It's composite sync, that much I know, but do I need it? Should it go to both V and H Sync, or what should I do?Besides this I think I can source some basic cable, and a couple of DIN connectors of the right type. Thanks for any help, I am planning on going into EE as a life career, but I haven't gotten to some parts yet.

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: August 07, 2017, 04:58:24 pm
content: It seems you'll need an LM1881, which will split the Sync to V-Sync:http://www.ti.com/lit/ds/symlink/lm1881.pdf.To get your H-Sync you'll need to follow the rest ofhttp://www.epanorama.net/documents/vga2rgb/vgamonitor.html

author: ebastler
author_rank: Super Contributor
timestamp: August 07, 2017, 05:43:56 pm
content: This threadhttp://nfggames.com/forum2/index.php?topic=4037.0suggests that the 1084 monitor will simply accept the composite sync from the Genesis on its HSYNC input. And, as a side note, it also seems to say that the 1084 will accept the NTSC-standard picture format. Fingers crossed!

author: Ampera
author_rank: Super Contributor
timestamp: August 07, 2017, 07:18:55 pm
content: Quote from: ebastler on August 07, 2017, 05:43:56 pmOf course it will if it's an NTSC unit. I however have a PAL unit. I do think it will work however.I talked to my dad about it and he reckoned that the composite sync should be wired to both H and V sync channels. I'll order the parts and see what happens.

author: ebastler
author_rank: Super Contributor
timestamp: August 07, 2017, 07:39:19 pm
content: Quote from: TwoOfFive on August 07, 2017, 07:18:55 pmGiven that the poster in that forum bought his monitor in the US, you might be right that he had an NTSC-ready model. But I agree with you that there is a decent chance that the RGB signals will be cross-compatible anyway.Regarding the sync signals, forum wisdom seems to agree that it is sufficient to wire the composite sync signal to the 1084's HSYNC input (which must have a built-in sync splitter). But it probably won't hurt to route it to VSYNC as well; and in any case it is easy to try both options. Good luck!