Sigma VGA card settings

Hello
I try to revive my old PC-1 (16K-64 K main board, dual diskettes). The problem is that I have no longer a CGA dispay to connect to.
The PC seems to work. I heard the diskette reading. I use a modified DOS that allow users of PC's with the original BIOS to attach a fixed disk or a VGA adapter. In my precious possessions I have found a card marked "Sigma VGA" It's a 34 cm long (13 inches) card http://parabolfr.free.fr/SigmaVGA.jpg
The card has a switch SW1 with 8 contacts and some jumpers.I would be grateful if someone could give me some doc or the settings of this card.
Regards

The early posts in thread http://www.vintage-computer.com/vcforum/showthread.php?t=9107 may help you.

Thank you, Modem7, for pointing me to this thread. However there are some discrepancies between the described cards and mine. Despite my efforts, I could not get a working configuration. But I'm not sure my card is still in good shape.

I have been given a Video 7 VGA card with the user's manual but without any driver.
I inserted the card into my PC-1, connected the card to my IIyama display and to my great surprise, it has worked at the first try. I could run the Dazzle program which is a IBM demo program that was used to demonstrate the IBM VGA display.

The BIOS date of my PC is 10/19/81

It's the reason why I'm obliged to boot with a special diskette that contains 2 files (CONFIG.SYS and BOOT.SYS) I don't remember exactly how it works (I could not find the source) I suppose it intercepts the DOS before it attempts a screen write.

The BIOS date of my PC is 10/19/81
It's the reason why I'm obliged to boot with a special diskette that contains 2 files (CONFIG.SYS and BOOT.SYS)

Click to expand...

Yes, as we know, that second revision BIOS doesn't recognise (then execute) the BIOS extension ROM found in cards such as the hard disk controller and EGA/VGA cards.

I inserted the card into my PC-1, connected the card to my IIyama display and to my great surprise, it has worked at the first try.

Click to expand...

Well, that surprised me. I had some time this weekend and decided to try the same thing. I have a 16/64K board with second revision BIOS, and I have an 8 bit VGA card. I could not get the VGA card to output anything. Replaced the second revision BIOS with a third revision BIOS, and VGA card working. That is what I expected.

So what's going on with your set up (VGA card working with second revision BIOS)? The only thing I can think of is that your VGA card is initialising itself as soon as it gets power. One hiccup I can see: During initialision, the VGA card's initialisation code alters the INT 10 vector (in low RAM) to point to code in the VGA ROM. Your VGA card needs to ensure that it only does that after the POST has finished doing its read/write check of low RAM.

An odd thing. The 8 bit VGA card I used was also a Video 7, but of course, mine could be a different version.

modem7 said:

...So what's going on with your set up (VGA card working with second revision BIOS)? ...

Click to expand...

As I have said, I use a modified DOS to boot the system. It allows user's of PC's with original BIOS to attach a fixed disk, or an EGA or VGA adapter and monitor. I boot the PC with this modified diskette which then ask me to replace the diskette with the diskette I normally use.
The modified diskette contains a CONFIG.SYS with an entry DEVICE=BOOTS.SYS
BOOTS.SYS is in fact a .COM program renamed .SYS It was written in assembler as a device driver. It intercepts DOS before DOS attempts a screen write. The author was an IBMer. Unfortunately I have lost the source and I can't give you more details on how the program works.
I can send you a copy of the diskette, when I'm able to copy it. Since yesterday I have a new problem: My PC refuses to start an I have no other mean to read a floppy diskette....

My video card is a Video 7 VEGA VGA compatible with VGA, EGA, CGA, MDA and Hercules standards. I have let he defaults settings.
On the PC switch positions 5 and 6 of SW1 set to ON

As I have said, I use a modified DOS to boot the system. It allows user's of PC's with original BIOS to attach a fixed disk, or an EGA or VGA adapter and monitor.

Click to expand...

Oops. I didn't pick up on the significance of the special boot diskette. Don't know why. You've made it clear in the first post.

I note that early 5150s with a Davong Systems hard drive also had a specialised boot diskette (see http://www.selectric.org/old5150/index.html).

I can send you a copy of the diskette, when I'm able to copy it.

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Thank you but no. I would have no use for it because I will keep my early 5150 as original as possible (I have other 5150s to play with).