Volt meter, Scope?

Could also trace the pins and what the jumpers bridge together

The unpopulated sockets is interesting, possible the card is inop? Though I guess other cards leave those empty, maybe a foreign language bios.

Some questions about a Hercules card

https://arvutimuuseum.ee/th99/v/P-R/50414.htm

https://www.dosdays.co.uk/topics/Manufacturers/tamarack.php

That card is probably the oldest I’ve seen with a shart branded chip, usually found those on PCCHIPS devices.

The best solution is oscilloscope, or at least a frequency meter.

MDA/Hercules monitors expect 18 kHz HSYNC, 50 Hz VSYNC.
CGA monitors expect 15 kHz HSYNC, 60 Hz VSYNC.

rmay635703 wrote on 2025-03-14, 15:56:

The unpopulated sockets is interesting, possible the card is inop? Though I guess other cards leave those empty, maybe a foreign language bios.

"Foreign language" is likely correct. "BIOS" is wrong, though. MDA/CGA cards do not have a BIOS, because the mainboard BIOS of the IBM PC (and all compatibles) include the code to interface with an MDA or CGA card. The big socket is for a character ROM, a ROM chip that does not contain any code, but the image of the 256 text mode characters. The card shown in this thread is a quite late MDA/CGA clone that has the standard "IBM extended ASCII" (aka Codepage 437) character set integrated into the main chip. So a character ROM is only required if some other character set is required, for foreign languages.

The small socket next to it contains the label "LS374". This is the type number of an 8-bit latch chip. This chip is either used to store the current character code (as the address for the character ROM) or the output of that ROM (the 8 pixels for the current scanline of the current character). It is used as an auxilliary chip to interface with the character ROM. My guess is that the chip will latch the character code, to keep the address bits to the ROM stable while the central chip reads the attribute byte.

Although this isn’t likely the exact card and there are some discrepancies my guess is this lines up

M/C should be mono/color, PTR should configure the parallel port (enable/disable/address).
From there on I can only guess that CG might enable/disable CGA and EMU could be emulating the CGA while in Hercules mode (like ATI small wonder does through software)

rmay635703 wrote on 2025-03-15, 19:29:

From there on I can only guess that CG might enable/disable CGA

No.
It toggles between the internal character generator ROM (integrated in the SARC chip), and the external character generator ROM (in the EXT CG socket).

EMU could be emulating the CGA while in Hercules mode (like ATI small wonder does through software)

I hope so! The other meaning could be that it emulates MDA on a colour monitor (CGA monitor).
Ie, that it understands MDA specific things like bold, underline, bright.
Or watches writes to MDA memory region, MDA registers etc.

Because that's something that used to be annoying.
Productivity software meant for MDA/MGA would blink like crazy if being used on CGA.
EGA/VGA were smarter. They could run with both MDA and CGA software.

Grzyb wrote on 2025-03-14, 16:46:

The best solution is oscilloscope, or at least a frequency meter.

I don't have an oscilloscope or a frequency meter, just a cheap multimeter - would it not be possible to use that? As far as I understand, I'd only need to check if there's a signal coming through on the pins that are only used by CGA. I know which pins shouldn't be used on MDA because the 5151 literally has them missing on its hardwired DB9 cable, so if I'm getting anything at all on those, then it's running in CGA.

Grzyb wrote on 2025-03-14, 16:46:

MDA/Hercules monitors expect 18 kHz HSYNC, 50 Hz VSYNC.
CGA monitors expect 15 kHz HSYNC, 60 Hz VSYNC.

So there's no chance it could be sending anything other than these two? I'm a bit worried it could be doing something weird like sending MDA at 15kHz / 60Hz - even though I know that wouldn't make any sense, I think.

Jo22 wrote on 2025-03-15, 21:39:

EMU could be emulating the CGA while in Hercules mode (like ATI small wonder does through software)

I hope so! The other meaning could be that it emulates MDA on a colour monitor (CGA monitor).

I hope so too, because the choice between "free compatibility with hundreds of games with no performance overhead" versus "destroying the monitor" is a bit of a no-brainer 😁

alfiehicks wrote on 2025-03-17, 09:01:

Grzyb wrote on 2025-03-14, 16:46:

MDA/Hercules monitors expect 18 kHz HSYNC, 50 Hz VSYNC.
CGA monitors expect 15 kHz HSYNC, 60 Hz VSYNC.

So there's no chance it could be sending anything other than these two? I'm a bit worried it could be doing something weird like sending MDA at 15kHz / 60Hz - even though I know that wouldn't make any sense, I think.

Other combinations are certainly possible:
Re: CGA/MDA/HGC test program
...but note that it's about *software* CGA emulation on generic "Hercules" cards.

That SARC chipset obviously does the emulation in hardware.
It may be similar to that of ATI GS/SWGS:
- CGA emulation on MDA monitor by double-scanning 75% of the scanlines, at normal MDA frequencies
- Hercules emulation on CGA monitor by interlace, at normal CGA freqencies

But it may be something different...