Does the vga bios for that card have a function that writes to that register/bit?
Do other drivers exist that use that register/bit ?

The video BIOS contains code to set bits 6-7 of CRTC register 0x31. See part of it in the following Ghidra disassembly. The clock select value to be programmed is in CH. Then it puts one bit into the (documented) "clock-select 2" bit of CRTC register 0x34, and the rest into CRTC register 0x31:

(Note, though, that I run this card in a non-x86 system. So the video BIOS does not get executed and I can't say which specific values would be written into the register.)

There is (in an IBM PS/2 document) a reference to a newer ET4000 data book, dated 1992. But no one seems to have scanned it?

Much of the VGA chips especially WD were made to interface with MCA bus as well but in practice I didn't see any produced besides cirrus logic.

Cheers,

To be clear: I merely used the citation from the IBM document as evidence that a newer data book exists for the ET4000; newer than the 1990 edition that is on Bitsavers and archive.org. This thread is still about an ISA card.

pentiumspeed wrote on 2023-02-06, 00:20:

Much of the VGA chips especially WD were made to interface with MCA bus as well but in practice I didn't see any produced...

I found at least 2 : "Matrox Magnum Graphics Controller MG-104, MG-108" and even all the software IBM released for them is preserved:

Re: 8bit PVGA1A OEM VGA for Olivetti. Drivers ?

but I confused WD95C01 with WD90C01, the real chip used in those is WD95C01.

I got to test an the older revision of the ET4000, marked TC6058AF. In that revision, the chip behaves as described in the 1990 data book:

• Pins 12 and 109 act as output enable for the video RAM,
• CRTC register 0x31 does not exist. I.e., it always reads back as zero, regardless of what you write to it.

In contrast, as described above, in the newer TC6100AF revision of the ET4000...

• pins 12 and 109 can be used as additional general purpose outputs, e.g., connected to the clock generator;
• they are controlled by bits 6-7 of CRTC register 0x31, which can also be read back.

Since no one so far came up with the updated edition of the data sheet, there's no way of knowing what other features were added to the TC6100AF revision.

PS: I forgot to mention: In the newer ET4000 (TC6100AF), the newly added, undocumented CRTC register 0x31 seems to work exactly as on the later ET4000W32i. As described, bits 6-7 control the clock select lines. Bits 4-5 are not implemented and always read back as 0. Bits 0-3 can be written and read, and probably serve as "scratch bits" without any functionality behind them.

Can someone explain in layman's terms what the effect of this difference would be for an end user?

If the graphics card manufacturer took advantage of the additional clock select pins – like on the card that started this thread – he could easily have the card select between more than the usual 8 pixel-clock frequencies. For the end user: If the video BIOS and/or driver knows about this, this can add more video modes or additional refresh rates to existing video modes.

(And in my case: I'm not an end user; I work on low-level drivers for these cards.)

mxmxmx2 wrote on 2023-02-17, 17:26:

If the graphics card manufacturer took advantage of the additional clock select pins – like on the card that started this thread – he could easily have the card select between more than the usual 8 pixel-clock frequencies. For the end user: If the video BIOS and/or driver knows about this, this can add more video modes or additional refresh rates to existing video modes.

(And in my case: I'm not an end user; I work on low-level drivers for these cards.)

Okay, good to know! I was just curious as to what it meant from a practical standpoint, and I can see now why that'd be a big deal.

Also, thank you for your time in doing this. Not many people are out there doing driver work to expand the capabilities of vintage hardware. 😀

I like to "bump" this thread because I have discovered yet another difference between the TC6058AF chip revision (as documented in the available data sheet) and the newer TC6100AF revision of the ET4000.

In the data sheet (and, hence, in the TC6058AF) pins 44 - 41 are used as address inputs A23 - A20:

However, in a TC6100AF-based ISA graphics card that I have tested, pins 43 - 41 are actually connected to the LA19 - LA17 (unlatched address lines) of the ISA bus. This only makes sense if those pins were reassigned a different function in the newer chip revision.

Hence, to repeat my question from two years ago: Does a data sheet for the newer revision (rev. F or rev. G, TC6100AF) of the ET4000 exist? If anyone has it, I'd be very happy to receive it.

hello
i checked out my collection and found that i have an early version of et4000. it was made in week 9002 and instead of et4000ax, its marked et4000c, and with no tc6058af or tc6100af code at all.
er i robbed the card off my former colleague about 16 years ago...

ET4000/W32i has a register that controls what these upper address line pins do, maybe the same register is used for these pins on the older chips too. The datasheet is too large to attach to this post but I imagine it won't be difficult to find.

Tiido wrote on 2025-03-06, 16:02:

ET4000/W32i has a register that controls what these upper address line pins do, maybe the same register is used for these pins on the older chips too. The datasheet is too large to attach to this post but I imagine it won't be difficult to find.

Yes, I know about the data sheet for the ET4000W32i. But that does not help me in finding all the changes in the ET4000 revision TC6100AF. (Like the address pin reassignment.)

noshutdown wrote on 2025-03-06, 15:31:

i checked out my collection and found that i have an early version of et4000. it was made in week 9002 and instead of et4000ax, its marked et4000c, and with no tc6058af or tc6100af code at all.
er i robbed the card off my former colleague about 16 years ago...

Fascinating. Out of curiosity: Can you post a photo of it?

mxmxmx2 wrote on 2025-03-06, 18:08:

Fascinating. Out of curiosity: Can you post a photo of it?

yes, here it is:

noshutdown wrote on 2025-03-07, 00:34:

mxmxmx2 wrote on 2025-03-06, 18:08:

Fascinating. Out of curiosity: Can you post a photo of it?

yes, here it is:

Hey, that is really similar to this one that I picked up several years ago. The design really is different from other ET4000 models, which was the main reason I grabbed it.

On mine the chip is marked ET4000AX TC6059AF. The board part number is lower than yours, but there are lots of differences so it's hard to say if one is older than the other. The fact that yours also has an EGA output is really interesting too.

Looking up the FCC ID, mine appears to have been made by DFI. It looks like it was a retail product too, since there is a tiny tiny thumbnail for an ebay listing in this post for a boxed card with the same name.

EDIT: Also, this may be the original software for the card? https://www.ebay.com/itm/365253084619

Ozzuneoj wrote on 2025-03-07, 08:18:

On mine the chip is marked ET4000AX TC6059AF.

... and it has a datecode of CW7 1992, whereas noshutdown's has a datecode of CW2 1990.

Thank you both for your photos. I had never seen those two chip revisions before.