dr.zeissler wrote on 2021-02-24, 18:10:

tested mce in cga-mode on tandy1000 rl/hd with nec71vm.
it works great. minor issue, textmode and graphicsmode differ up to 5mm to the left.

will check if I can get a smaller image-setting so everything is visible.

Differ to what?
I had the same problem of the picture starting drawing very close to the edge, like in the overscan area of a regular TV. Using a Tandy 1000HX. The composite output is fine, I can only assume it's how the RGBI output is done, as it was expected to be displayed on a CGA monitor without overscan (while a TV uses the composite cable.)

Autocenter on TFT in textmode (like volkov/norton commander).
Monitor is on 640x240 Pixels.
Starting a game the picture in graphics mode seems to be shifted 5mm to the left.
Option1: Autocenter on TFT
Option2: Moving the picture 5mm to the left and making it a bit smaller.

though the image is better on function "auto center" on TFT I currently push the center-button on changing text/graphics-mode.
not perfect, but best quality.

the GGLabs dongle does support 6-bit RGB, you have to change the DIP switches to enable it though

Hello and welcome,

A very old device sends a TTL signal in the CGA standard, but monochrome, i.e. RGB as one signal. I would like to get a monochrome CVBS signal from this. It's probably much simpler than your MCE project. Can I ask you for a diagram?

Best regards, Jan Kobior
jkobior@gmail.com

quote=scorp post_id=934661 time=1612624830 user_id=40266]
Hello there,

just wanted to briefly introduce another small project of my - a MCE-Adapter. You can use it to connect old PCs to a 15kHz capable RGB/VGA Monitor or to use it with Sync converters like GBS-8200. I made it to be able to use my Hercules, CGA and EGA graphics cards, but may be someone else will find it useful as well. The project is completely open source, both hardware and software.

Features:
- Converts digital MDA, Hercules, CGA, low-res EGA, high-res EGA to analog RGBS or RGBHV/VGA signal
- Color DAC for 3, 4, 16 and 64 color modes
- Switchable composite sync from H- and V-Sync
- Loop through HV-Sync, colors conversion only mode
- Switchable composite sync inversion
- Includes IBM's "brown-hack"for CGA and 16-colors EGA modes
- Switchable green and white monochrome screen emulation

You can find the project here:
https://github.com/necroware/mce-adapter

I also made a video series about it on my youtube channel, if you are interested:
https://www.youtube.com/watch?v=7c3yLX52ZEs&l … uGk6_uk54765G1t
[/quote]

I got a kit and built the MCE adapter with the intent to use a Sony PVM 1350 to display a CGA signal. Which isn't exactly working and I'm trying to determine why. 15khz RGBs signal should work, I'm using a VGA to BNC cable. I have managed to get 15khz RGBHV to display on an Acer P216hl LCD, which accepts the 15khz signal fine. The aspect is a bit stretched but I have a good image.

Never tested with that display, so I don't know if it would work there at all. From pictures it seems to have only RGB with composite sync, so at least you have to set the jumper accordingly to set it into RGBS. If you do that, do you get anything? May be scrolling screen or something similar?

scorp wrote on 2025-01-31, 18:59:

Never tested with that display, so I don't know if it would work there at all. From pictures it seems to have only RGB with composite sync, so at least you have to set the jumper accordingly to set it into RGBS. If you do that, do you get anything? May be scrolling screen or something similar?

Everything I understand about RGBi is that if you combine HV into Composite Sync. Run that into any PVM or similar CRT with RGBs inputs, you should get a picture but the colors would be incorrect.

Basically all PVMs support 15khz RGBs, some newer models actually support 31khz and higher. Some even have an input that accepts RGBi.

In my understanding there is no reason aslong as I have the jumper set for RGBs that it wouldn't work for CGA/EGA which run at 15khz. However my PVM will not accept 18khz or 21khz.

So the adapter should correct the colors and on paper work with any PVM or Scart TV etc. With RGBs. I'm not an engineer. So I don't really understand why I get nothing on the screen.

Turns out, I'm having some problem getting the correct Csync from the MCE adapter. My CGA card also has CGA Composite, while not a clean Csync. When connected to RGB ext. Sync the CGA color and picture works correctly on PVM 1350 using RGBs inputs.

May be C-Sync has to be look different on this device. Unfortunately I have only GBS-8200 to test which also uses C-Sync. Would be nice if you'd open an issue on the project site. If you are able to program the GAL, we can experiment a bit and I'll provide a different firmware for testing.

I don't currently have the ability to program chips. I usually buy a kit or assembled board when they require a programed chip. However I don't mind doing some testing.

Issue 10 on the project site. Refers to an issue with the C2 value being to low for CGA C-SYNC to work properly. I thought this might be the same problem. They so tests of 2.2uf and 4.7uf. So perhaps I should be trying one of those values or perhaps a different value?

Yes please, try 4,7uf and report if that works for you.

I replaced c2 with a 4.7uf. It doesn't seem to make any difference in my case.

I'm not completely sure how the MCE adapter is Combining HV into Csync. I have found a circuit that applies to CGA to SCART. However my idea is to just build the HV to Csync part and attempt to use it correct the Csync. I think I need 5v on R7, however the R8 can be removed along with the RGB grnds.

I tried this circuit for HV to Csync from retrorgb, not entirely sure being its intended for VGA that its CGA compatible. It didn't seem to correct my sync. However I just sort of slapped it together. Tried pulling HV from inputs on the GAl and routing the Csync to pin 15.

Not sure if I'm actually trying something different or just duplicating what the MCE adapter is already doing?

I'm seeing the issue also might be that the CGA HV sync are both Positive. Combineing them is probably still a Positive Csync. According to info on the PVM 1350 the Csync input is Negative. I'm seeing that I can run that through a 7404 and that will invert the Positive Csync to Negative Csync.

I ran the Csync through the 7404 hex inverter. That corrected the CGA Sync polarity to Negative. Which now works correctly on PVMs.

However I'm not sure if you redesign the adapter to change Csync Polarity to Negative would have a negative effect on any other displays or video devices such as GBS8200.