CGA / RGBHV compatibility?

[TheHexaCube]

Hi!

First of all, kudos for the amazing project you have built!

I have stumbled upon the GBS-8200 and your CFW as I am looking to replace a broken CRT with some (any!) TFT of a cnc milling machine.

The CNC-Controller provides a RGBHV signal, with 5V TTL signals as far as I can tell (based on information available)

I have found out that the GBS-8200 with stock firmware will not handle this, and instead requires an analog RGBS signal, ie. RGB being 0-1V, and also a composite sync signal.

This seems to be often accomplished by using an XOR + Inverter circuit for converting H-/V-Sync to C-Sync.

It is, however, a little unclear to me at the moment whether or not this fix is required, nor will even work to begin with, for your CFW.
It is also slightly unclear to me, what signal level the sync-inputs can handle/require.
(EDIT: It appears that the maximum input voltage for the GBS is around 3.3V, but 1V is the "supposed" input levels? Is that a correct assessment?)

I would love for some elaboration on what is, or is not, needed for this to properly work.

Looking forward to a reply and thanks again
Best regards!

[eparadis]

I can't answer your question, and it sounds like you're going to have to do some level shifting interface circuitry for your application.

But before you get too far, I was looking into using this as a CGA replacement and found that the docunmentation more or less states that this can't do any of the useful video modes you would likely be interested in:

https://ramapcsx2.github.io/gbs-control/Wiki/Tested-video-modes.html#ibm-pc-and-compatibles

CGA (640x200)
VGA     ATi Mach 64     03h     VGA     640x200     ?????     ?????     NO
VGA     ATi Mach 64     06h     BIOS     640x200     ?????     ?????     NO
VGA     ATi Mach 64     0Eh     BIOS     640x200     ?????     ?????     NO

IBM mono (720x350 text only)
VGA     ATi Mach 64     07h     VGA     720x350     ?????     ?????     NO

Herc mono (720 × 348)
VGA     ATi Mach 64     1Bh     VGA     720x400     ?????     ?????     NO
VGA     ATi Mach 64     1Ch     VGA     720x400     ?????     ?????     NO
VGA     ATi Mach 64     97h     VGA     720x400     ?????     ?????     NO
VGA     ATi Mach 64     C3h     VGA     720x400     ?????     ?????     NO

If I find out more definitive information, I'll update this post. And I welcome any corrections to the above information. It's straight off the docs page.