space_eraser wrote on 2025-03-13, 01:42:

Hi all,

I have OTI067 ISA VGA with VGA BIOS 1.05 which posts 1MB RAM. VGA was in local store for a long time. There are 4 DRAM chips TMS44C256-10N. Its 100ns 256Kx4bits chip. Some sotware detects 512k, some 1024k. Is there any chance to verify what is right value ?

As you said, the chips are 256k x 4bits, so they are 128KB each and there are four chips. There can only be 512KB total on the card in this configuration. Not sure why some things are reporting 1MB but it can't be correct unless there are more memory chips elsewhere (which there don't appear to be).

It's 512 KB, period.
OTI067 doesn't even support more.

I suspect somebody faked the BIOS to sell that card as a 1 MB one.

BTW: can you dump the BIOS of that card, eg. using NSSI ?

I would like to have a look at that...

Seems very strange because it is a by-the-books Oak card with the original BIOS chip sticker and an Oak FCC ID.

It's basically identical to one shown at VGA Legacy:
https://www.vgamuseum.info/index.php/cpu/item … 325-oak-oti-067

Grzyb wrote on 2025-03-13, 03:07:

BTW: can you dump the BIOS of that card, eg. using NSSI ?
I would like to have a look at that...

Ofcourse see attached file.

Grzyb wrote on 2025-03-13, 02:57:

I suspect somebody faked the BIOS to sell that card as a 1 MB one.

If somebody, then probably someone in factory. It seems original.

Ozzuneoj wrote on 2025-03-13, 03:23:

Seems very strange because it is a by-the-books Oak card with the original BIOS chip sticker and an Oak FCC ID.

It's basically identical to one shown at VGA Legacy:
https://www.vgamuseum.info/index.php/cpu/item … 325-oak-oti-067

Yes interesting. Also RAMDAC, ROM and DRAM chips are socketed in my version. The other cards with the same OTI067 have these chips soldered without socket, or partialy socketed but not all.

That BIOS is identical to one of the BIOSes found here - https://www.vgamuseum.info/index.php/companie … 326-oak-oti-077

So it looks genuine - just buggy.
It supports various chips: 057, 067, 077.
Correctly identifies the 067 chip, but misidentifies the RAM size.

You can try replacing it with an other 057/067/077 BIOS.
Or with the 067-only BIOS found here - https://www.vgamuseum.info/index.php/companie … 325-oak-oti-067

Grzyb wrote on 2025-03-13, 02:57:

It's 512 KB, period.
OTI067 doesn't even support more.

Oh, didn't know about that limit. This likely explains the well-known mediocre performance of many (but not all) OAK graphics cards: The OTI067 obviously only supports a 16-bit memory bus. On the other hand, "my favorite OAK" (as I like to call it) easily achieves 4MB/s ISA performance and has a programmable clock generator built into the RAMDAC (called "SYNDAC" according to the BIOS). This card must be using the OTI077 in 32-bit mode.

EDIT: Deep link on VGAmuseum to a card that is likely similar to my favorite OAK: https://www.vgamuseum.info/images/vlask/oak/oti077fb.jpg - but I am quite sure my card has a DIP RAMDAC which is not MUSIC branded, but electrically compatible. Non-Deep link to the OTI-077 page: https://www.vgamuseum.info/index.php/cpu/item … 326-oak-oti-077

Grzyb wrote on 2025-03-14, 09:01:

You can try replacing it with an other 057/067/077 BIOS.
Or with the 067-only BIOS found here - https://www.vgamuseum.info/index.php/companie … 325-oak-oti-067

Thanks for help. Can you investigate some experience with replacing original ROM/PROM with EPROM/EEPROM? It seems there is some limitation in total length of VGA BIOS dumped from shadow RAM by NSSI. My version dumped by NSSI has 32kB and original from vgamuseum website has 64kB. I am using XGecu T48 programmer but the issue is to resolve original PROM chip. It seems original VGA BIOS is 64kB, it means for example EPROM 27512. But is there full pin compatibility with original factory programmed chip, which is usually PROM without labels?

All I know is that the oti067.zip -> BIOS.BIN file is 64 KB, but the second half is all FFs.

It's likely that only the first half of the ROM is mapped into the CPU address space.

You can experiment - when using EEPROMs, there's nothing to lose.