1. More than 1 MB on GD542x only adds INTERLACED modes - does your monitor support it? Most (or even all?) LCD monitors don't.

2. Is the second megabyte of the same type as the first? FPM is probably necessary, not EDO.

Guld wrote on 2024-12-30, 20:09:

- Anything using over 1 MB of video memory produces an unstable image

It would be a bit uncommon that memory usage would affect whether the video signal sync is stable or unstable. Rather, it is more likely that the pixel clock, hsync and vsync rates and the timing geometry of the video mode is what affects whether the signal is stable or not.

The video mode 1280x1024 at 16 colors requires 1280*1024 / 2 = 655,360 bytes of memory.

Whereas 1280x1024 at 256 colors requires 1,310,720 bytes, which is more than 1,048,576 bytes (1MB limit).

So you can try with the 1280x1024 at 16 colors mode to verify this memory usage hypothesis. If that mode doesn't sync, then it is likely not the memory usage amount that is causing the problem.

If 1280x1024 with 16 colors syncs, but 1280x1024 with 256 colors does not sync, then it would lend validity to the issue being something memory usage/memory bandwidth related.

Like was mentioned above, I think CL-GD5428/9 can do 1280x1024 video mode only as interlaced. For 1024x768 it should be able to do either interlaced or noninterlaced.

So if 1024x768 works for you and you are not sure if that was interlaced or noninterlaced, you can try using the Cirrus Logic CLMODE utility to force the refresh rate of that video mode to be interlaced. This allows testing whether your LCD/CRT can sync to interlaced modes.

Ah...thanks, I didn't know about CLmode, that helps because it displays some info about interlaced modes (which I had completely forgotten about).

Neither 1280x1024x4 (16 color) or 1280x1024x8 (256 color) work.

Neither does 1024x768...unless I set it to a monitor which will cause it to output non-interlaced...Then I can see the output (working on an older LCD panel here).

So that looks like what is going on and explains why some of my equipment seems confused about the vertical rate when one of these interlaced modes comes up. So...now to see if I can get the interlaced modes to work via any of my video equipment 😁.

Anyone know of a good converter that can handle the interlaces inputs and output something useful? If I can figure out anything with the equipment I've got I'll post something.

Thanks!

I have developed CRT Terminator Digital VGA Feature Card ISA DV1000 to handle interlaced video modes. It displays them as progressivized. For example, on a Diamond SpeedSTAR 64 (CL-GD5434), Windows 3.1 in interlaced 1280x1024 256 colors mode captures like follows:

although it should be noted that such use case is overclocking the Feature Connector way beyond the original VESA rated limits. Nevertheless, with a good quality VGA card, it can work.

clb wrote on 2024-12-30, 22:27:

I have developed CRT Terminator Digital VGA Feature Card ISA DV1000 to handle interlaced video modes. It displays them as progressivized. For example, on a Diamond SpeedSTAR 64 (CL-GD5434), Windows 3.1 in interlaced 1280x1024 256 colors mode captures like follows:

although it should be noted that such use case is overclocking the Feature Connector way beyond the original VESA rated limits. Nevertheless, with a good quality VGA card, it can work.

Thanks for sharing! I had run into your card once before and it certainly looks interesting!