Do you have video settings in BIOS?

DundyTheCroc wrote on 2023-06-14, 08:18:

Do you have video settings in BIOS?

Not really, nothing that could disable one or the other, unless I'm mistaken. Is there a specific option I should look for?

Thanks!

See this thread, a very efficient method using the debug command: Re: C&T 65550 CRT BIOS

Thermalwrong wrote on 2023-06-14, 20:26:

See this thread, a very efficient method using the debug command: Re: C&T 65550 CRT BIOS

Thank you so much for pointing this out! I apologize, I didn't search the forum hard enough before asking.

The solution didn't quite work for me yet, apparently when I set the flag? for the addresses indicated in the post, it goes into a video mode my monitor can't show (it's an lcd monitor, not a CRT, that might be the issue?).
Reading the manual now for some info, but looking into another solution to test this out.

That's a shame, I wonder what's different. It's definitely a C&T CT65550? Personally I don't know much about this debug option because I use the built-in flat panel more.

Check out this page: https://www.advantech.com/en-eu/support/detai … /faq?id=1+FY+68
Using CBROM you can extract the VGA BIOS, though I found I had to use a later version of cbrom than what's on that page. I used 1.26B successfully to get the VGA BIOS out.

Hopefully your resulting VGA BIOS is 32KB in size, because that's the only kind I know how to edit, no known editor for the larger 48k BIOS. BMP32K50 should be able to open the VGA BIOS (syntax: "bmp32k50.exe vgabios.bin") for a CT65550 and you can change the display mode in there - I do this in dosbox-x on my main PC. Once edited you'd integrate the VGA BIOS back in and reflash the new BIOS.
Here's the setting to change a few pages in, it should only require changing this one setting:

I do recommend checking the product's manual and BIOS thoroughly though because many of them implement jumpers or BIOS settings to control the LCD output and that could be causing problems for you. If there are jumpers/BIOS settings to change, perhaps setting the LCD display to 1024x768 could allow the VGA output to behave more correctly.

Thank you very much for this information!

I'm still trying to make the previous solution work because I'm afraid to modify the BIOS, to be honest. It's not due to lack of experience, but I recently bricked an RX5600xt and I still haven't found the "time" to find how to unbrick it, 🤣.

Yup, mine is definitely a CHIPS 65550 (that's how I found the driver)

I still believe that when I do:

1o 3d0,1
2o 3d1,1
3q

it switches to CRT, but for some reason it goes into a mode my LCD monitor can't display (it shows a message with the error). It's consistent with the datasheet for the 65550, because if I (blindly) type "o 3d1, 2" (I believe, I'm typing this from memory) it goes back to dual mode and I get back the display (at 640x480, of course).

To test this, I'm looking for a way to change the resolution via script or command line, so that I can blindly set the video mode to 1024x768 @ 60hz and see if I get video.

Or am approaching this the wrong way?

Thanks again!