I have no experience with this sorta of thing and thus unlikely to be any help, but I do like to learn so I googled the manual and noticed under Primary Display one of the options is: Not Installed. Also under Video Rom Shadow one of the options is Absent.

I’m curious what/how exactly can you tell is occurring without a video adapter? Can you manipulate the bios settings at all? (Maybe modify bios defaults offline then and flash it?)

since your board has video on board, my guess its looking for Monitor DDC to report output presence.

BloodyCactus wrote:

since your board has video on board, my guess its looking for Monitor DDC to report output presence.

DDC was fairly modern invention, its more likely to be checking impedance on analog outputs
https://www.geeks3d.com/20091230/vga-hack-how … vga-dummy-plug/

BloodyCactus wrote:

since your board has video on board, my guess its looking for Monitor DDC to report output presence.

Maybe I'm looking at the wrong manual / images, I don't see any evidence of video on board.

BinaryDemon wrote:

BloodyCactus wrote:

since your board has video on board, my guess its looking for Monitor DDC to report output presence.

Maybe I'm looking at the wrong manual / images, I don't see any evidence of video on board.

yep, nothing on https://stason.org/TULARC/pc/motherboards/A/A … 86-SBC-400.html

from a bios perspective it needs something to hook int10 and provide basic functions, a dummy firmware

BinaryDemon wrote:

BloodyCactus wrote:

since your board has video on board, my guess its looking for Monitor DDC to report output presence.

Maybe I'm looking at the wrong manual / images, I don't see any evidence of video on board.

oh I was looking at the wrong AAEON SBC

The board has indeed no on board video (that's a different SBC, I have one of those too).

What would be the most simple video card, from a low level programming perspective? Hercules?
Where would I find detailed programming information?

BinaryDemon wrote:

I have no experience with this sorta of thing and thus unlikely to be any help, but I do like to learn so I googled the manual and noticed under Primary Display one of the options is: Not Installed. Also under Video Rom Shadow one of the options is Absent.

I’m curious what/how exactly can you tell is occurring without a video adapter? Can you manipulate the bios settings at all? (Maybe modify bios defaults offline then and flash it?)

It just beeps like an ordinary BIOS that lacks a video card.
The BIOS is a bit awkward to use, it has a 'gui', but I can enter the BIOS and do some basic modifications.

bios might use this maybe? http://stanislavs.org/helppc/int_10-1a.html
I dont know, havent looked into any bioses code, MDA is the simplest card
I never tried running such old hardware with no graphic card, more modern stuff will beep but it wont stop it from booting
looking up BIOS Data Area in bios companion book:

187h 135 Int 10h 1 byte Video display adapter options
2Bit 7 - bit 7 of last video mode
30b = clear display buffer setting mode
41b = do not clear the display buffer
5Bit 6-4 - memory on video adapter
6000b = 64Kb
7001b = 128Kb
8010b = 192Kb
9011b = 256Kb
10100b = 512Kb
11110 = 1024Kb or more
12Bit 3 - video subsystem
130b = not active
141b = active

Bit 3 - video subsystem
0b = not active

looks like it should "just work"