I'm sure these chips are on more cards than just the Pure3D's from Canopus but that's not relevant to the question I have.

On the Canopus we find a Chrontel chip, this chip turns VGA signals into PAL/NTSC signals.
http://www.datasheetcatalog.org/datasheets2/20/204066_1.pdf

However, there's also an Atmel chip;
http://www.atmel.com/dyn/resources/prod_documents/doc0364.pdf

As far as I can tell from reading the datasheet, it's a PAL emulator. I'm sorry, what? Why would there be a need for an emulator if there's already a converter (the Chrontel chip) ??

Can somebody please explain the function of that Atmel chip to me? How does it relate to the Chrontel chip?

Emulation?
No, nothing to do with emulation. The atmel is a CMOS chip, with an erasable and programmable flash memory area, just like many eeprom bios chip on motherboards and VGA.

Then, what is it's function on the Voodoo cards?

NitroX infinity wrote on 15.01.11 at 22:08:15:

Then, what is it's function on the Voodoo cards?

Isn't obvious ? It stores the videocard BIOS.

u20 can also be used with an other, smaller IC

as far both ICs missing on the non TV-out version i would say both chips are need for the TV-out
http://tdfx.de/pic/pure3dlx_01b.JPG

http://tdfx.de/pic/pure3d_01b.JPG

RaverX wrote on 16.01.11 at 00:44:32:

NitroX infinity wrote on 15.01.11 at 22:08:15: Then, what is it's function on the Voodoo cards? Isn't obvious ? It stores the videocard BIOS.

Voodoo Graphic cards do not require a BIOS. Though I suppose it could be used to store information about PAL/NTSC resolutions?

NitroX infinity wrote on 16.01.11 at 13:52:18:

RaverX wrote on 16.01.11 at 00:44:32: NitroX infinity wrote on 15.01.11 at 22:08:15: Then, what is it's function on the Voodoo cards? Isn't obvious ? It stores the videocard BIOS. Voodoo Graphic cards do not require a BIOS. Though I suppose it could be used to store information about PAL/NTSC resolutions?

No, it couldn't.

Look at the pictures posted by exxe (thank you, exxe). You should notice an important difference between the two layouts beyond the atmel and chrontel chips.

Every Voodoo Graphics chipset (as every VGAs chipset) needs a crystal oscillator, in order to stabilize the chipset pixel clock signal. This is important to provide a stable image on the screen, at fixed resolution and refresh. Looking at first picture, you can find the crystal oscillator at the bottom of the card, under the ICS gendac.

But in the second picture, which displays the layout with TV out capabilities, the crystall oscillator is placed in the upper part of the board, beside the chrontel chip.

Now, also the chrontel chip need a crystal oscillator, but as you can see, there is only one. My guess is that the atmel chip is used as crystal oscillator replacement ;)

You can read the description for pin 17, page three of chrontel datasheet, to find a confirm about that.

To me it looks as both cards have a quartz just in different locations Y1 vs Y2. As to the Atmel chip I was thinking that i might have something to do with the special features Canopus provides with it's sw like the Witchdoctor setup to pass all signals to the Spectra2500.
My two cents on the matter.
Cheers,
G1nX

G1nX wrote on 16.01.11 at 16:37:01:

To me it looks as both cards have a quartz just in different locations Y1 vs Y2.

Right, but in case of TV capabilities, the chrontel chip would need a crystal oscillator as well, while in the TV version of the card you can see there is only one oscillator.

This could be explaned by the presence of the atmel chip indeed, a replacement of the crystal oscillator.

You only need one quartz because it serves the same function it only depends if it will handle VGA only or VGA + TV-out thus the different location on the board. See a similar scenario on Rush cards:
http://www.tdfx.de/pic/helios_rush_01.JPG
http://www.tdfx.de/pic/adrenaline_rush_01.JPG
An these don't have an Atmel chip only the BIOS chip (various brands).