1200XL PAL GTIA Adapter Board - Gauging Interest

[flashjazzcat]

OK. So I've established that PAL is isolated on the 1200XL if jumper W10 is removed. Therefore, we can have a low-profile adapter with 1-1 connections, with the second oscillator's output fed to the GTIA PAL input. Yes?

[Dropcheck]

Why don't you use the schematics to the XL or XE computers to see what OSC and PAL (pins) are used for in these computers?

 

OSC is always used. It is the main system clock source in all boards and GTIA/CTIA variations. PHI0 and PHI2 are derived indirectly from this input.

 

PAL is used only on PAL GTIA chips. The pin is not connected on GTIA NTSC chips.

 

Which explains on a 1200XL why the jumper W10 is not connected. It never was released as a PAL version. True?

 

XL schematics show a jumper to connect this pin to OSC. This would affect PAL GTIA chips only.

 

1200XL NTSC to 1200XL PAL complete conversion sans TV Modulator

 

The 800XL PAL has 2 crystals

 

So the question becomes/remains do we need to:

 

1. Replace the main OSC circuitry entirely and then close W10 jumper or

 

2. Add additional circuitry (ie PAL crystal connected to the PAL pin on a PAL GTIA) and not close W10 or

 

3. Replace the main OSC circuitry entirely, add additional circuitry to the PAL pin and still not close W10.

 

Edited December 28, 2011 by Dropcheck

[Mathy]

Hello guys

 

Remove the jumper and add the extra circuitry. (Just had a look at both the 130XE and the 800XL's schematics)

 

The jumper is only needed for NTSC machines, the extra circuitry is only needed for PAL machines.

 

Mathy

 

PS I'm not sure if it would be possible to add some kind of switch(ing circuitry), so that one could choose between NTSC or PAL.

Edited December 28, 2011 by Mathy

[Defender II]

I'd like at least one. When a final cost is established, I can let you know if it should be bumped up to two.

[Dropcheck]

Hello guys

 

Remove the jumper and add the extra circuitry. (Just had a look at both the 130XE and the 800XL's schematics)

 

The jumper is only needed for NTSC machines, the extra circuitry is only needed for PAL machines.

 

Mathy

 

PS I'm not sure if it would be possible to add some kind of switch(ing circuitry), so that one could choose between NTSC or PAL.

 

I'd think you'd have to have both the PAL Y1 and Y2 circuitry on a board to switch between original NTSC to PAL. But then to be really be one or the other you'd also have to have both PAL and NTSC chips and then you'd .......... Well you get the picture. Might as well completely redo the motherboard. Way more than a hobby project. I suppose it could be done, but at what cost and hassle?

 

So you're suggesting that Y1 would have to be replaced and the circuitry for Y2 connected to the PAL and OSC pins on the GTIA and W10 jumper not closed?

[Mathy]

Hello Dropcheck

 

Do you have a schematic for the 1200XL, so that I can check?

 

Mathy

[Dropcheck]

Hi Mathy,

 

I wish I did. I'm flying blind here. I have a mod schematic that's been floating around here for awhile that flashjazzcat sent me http://www.atariage.com/forums/index.php?app=core&module=attach&section=attach&attach_rel_module=msg&attach_id=228073

 

I have the NTSC 800XL schematics and flashjazzcat has put a link to the PAL versions a few posts ago. Just trying to put the pieces together. But .....

[Mathy]

Hello Dropcheck

 

I don't have permission to look at the attachment...

 

But I looked at the link Jon posted, yikes, the Jerzy schematics. But if you look at the first gif (800xl_01.gif) you'll find OSC and PAL in the lower left corner. The 74LS74 stuff and the stuff around it. That's what we need to create the PAL (timing) signal for the PAL machines.

 

If I'll ever find them in the mess behind me, I'll have to scan the original schematics by Atari. The Dutch Atari User Group (Stichting Atari Gebruikers) once sold them to members. I was one of them. BTW Guus Assman (who visited AtariAge from time to time) was their president (SAG, not Atari) at some time.

 

Mathy

[Dropcheck]

Hi Mathy,

 

Sorry here's the image

[Dropcheck]

Yea I looked at the schematics he linked to. Looks very close to the image above.

[flashjazzcat]

To be clear, the plan was to incorporate the Y2 circuit on the adapter board. Switching between PAL / NTSC on the fly is too complex for the reason Dropcheck has already described.

 

For a permanent PAL conversion, the user would have to replace the main oscillator (Y1), replace Antic and GTIA with PAL versions, and put the adapter board under GTIA. If W10 is already vacant, that's the job done. The only soldering should be for the main oscillator on the motherboard. The main clock is linked to the Y2 circuit to regulate it, as I understand, so it doesn't drift out of sync with the rest of the system. So there should be no need for cut traces or offset header pins.

 

In my case, this adapter ideally needs to be about 5mm high including the height of the socket in order to fit underneath an overhanging VBXE board. This can only be done if the adapter is similar to the VBXE Antic adapter in construction. The headers may cost a little more, but 1) square header pins commonly found on offset adapters destroy machine sockets and won't fit in precision sockets, and b) there's no point in making the board bigger than it needs to be.

Edited December 29, 2011 by flashjazzcat

[Mathy]

Hello Jon

 

Looks like it. I can't find the above Y1 circuitry on the 130XE schematics, but the XE derives it's OSC signal from the 14.something clock signal that the Freddy chip divides by 4. I guess the 1200XL doesn't have a Freddy chip, but you never know.

 

Mathy (who doesn't feel like opening his 1200XL)

[Gunstar]

Count me in for at least one, probably two.

 

@Gunstar - a true PAL machine should run pretty much all NTSC software. Switching from the NTSC/50 you have now to a true PAL signal will change the following:

 

Output signal will be true PAL, and require a PAL compatible monitor. Many North American colour monitors could handle a 50Hz signal as long as it was still NTSC colour encoding. The updated machine will now be transmitting PAL colour signals. Your 110V Commodore 1701/1702/1084 will only show black and white.

 

Artefacted colours wont work anymore.

 

Software that inspects the PAL/NTSC personality of the GTIA will now see PAL, not NTSC.

 

I have a PAL 800XL, an NTSC 1200XL and a quasi-PAL 1200XL. I cant think of any software that runs on the quasi-PAL 1200XL that wont run on the 800XL.

 

Thanks, that is good to know about the compatibility, but the fact that my 50/60Hz 1084S would only show B/W is a big turn-off. I don't want to have to get another monitor PAL CRT or a PAL compatible LCD monitor, not until my 1084S stops working, which will hopefully be a very long time. I'd rather have my quasi-PAL 1200XL that runs most PAL software, especially since it's mostly just demos that don't work, every PAL game I've tried works fine on my Quasi-PAL 1200XL.

[flashjazzcat]

Thanks, that is good to know about the compatibility, but the fact that my 50/60Hz 1084S would only show B/W is a big turn-off. I don't want to have to get another monitor PAL CRT or a PAL compatible LCD monitor, not until my 1084S stops working, which will hopefully be a very long time. I'd rather have my quasi-PAL 1200XL that runs most PAL software, especially since it's mostly just demos that don't work, every PAL game I've tried works fine on my Quasi-PAL 1200XL.

 

This reminds me of another interesting point. When I still had the NTSC chips in the 1200XL, my 1084S-D2 would only display a mono picture, although I was told the PAL monitors were dual-standard. None of the LCD monitors I own have any trouble whatsoever coping with the NTSC signal.

 

For information, VBXE2 is a neat way of solving NTSC / PAL monitor problems. The Commodore monitors accept the RGB signal regardless of which Antic / GTIA chips and oscillators are fitted.

[Gunstar]

Apparently the 1084 dual-standard (on both NTSC and PAL versions) only applies via RGB. Other than that, they can handle the different refresh rates through composite/s-video, but not the different color standards. Your example of your color problems with the 1200XL on your PAL 1084 as well as your VBXE point prove this theory. I also never had a problem using 50/60hz ST software on my 1084, becuase it was via RGB and people here say the NTSC 1084 will have the same mono only problem with PAL machines that you have with your 1200XL on your PAL 1084.

 

It seems to me that some sort of NTSC/PAL color signal converter would be a much simpler answer than relying on obtaining a compatible monitor.

Edited December 30, 2011 by Gunstar

[mimo]

First off, rgb is rgb it is not region specific.

Some 1084s are dual standard, a friend of mine has a pal 1084 that he uses with an av moded 5200 and ntsc 800. No such luck with either of my 1084s though.

Iirc some of the ntsc ones are switchable between pal and ntsc?

Edited December 31, 2011 by mimo