I want to trade a PAL GTIA for an NTSC GTIA

[Gunstar]

Here's the deal; about a year or so ago I ordered a replacement GTIA chip for an NTSC 8-bit I'm rebuilding, but just recently got back to rebuilding it. Unfortunately I ordered a PAL GTIA from Best Electronics by mistake, and I no longer have the reciept and it's been so long I don't think I could exchange it anyway. It actually costs $10 for the PAL and only $5 for the NTSC version from Best E. anyway, so if someone has an extra NTSC GTIA and needs a PAL, or wants one for backup or whatever, you'd be getting a deal. So, I know it's a long shot, but is there anyone who wants to trade their NTSC GTIA chip to me for a PAL? I know I'm not talking about much money anyway, but I hate to see this PAL GTIA go to waste and I still need the NTSC chip, so...a couple $ for shipping is still cheaper anyway. Even if Best E. would still exchange it, with shipping there and paying for return shipping it'd cost me about the same as just buying the $5 NTSC chip straight out. So, anyway I look at it, if I can find someone who wants to trade, one way shipping for each would save us both money and no chip would go to waste (collecting dust unused).

Edited December 1, 2007 by Gunstar

[Evidious]

I spare GTIA Chip If you want it. C014805 is the atari part number right?

[atariksi]

I happen to have a spare tested and working NTSC GTIA chip and some other stuff too if you need it... I'll swap for the PAL version.

 

If you also want me to ship you anything else with the NTSC chip, let me know.... Currently, I have up for auction a simulator that's very useful for testing stuff like keyboard, joystick ports, etc. using a PC hook-up:

 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...em=320189144289

 

You can email me at [email protected]

[Gunstar]

I spare GTIA Chip If you want it. C014805 is the atari part number right?

 

That's the right part. Wow! 2 people and I thought it would be a long shot for 1...

 

I appreciate both replies, I guess I'll have to go with Evidious since he replied first, unless it's more important to atariksi and no big deal to Evidious...

The PAL chip I have,C014889 is untested (by me) but was bought new from Best Electronics so it should work fine. Evidious, do you care if I trade with atariksi since his is tested? You were first, so if you really want to trade I'll take my chances that yours works fine too...

Edited December 1, 2007 by Gunstar

[Evidious]

It's fine with me if you want to trade with atariksi. Good Luck with your project

[antec]

Waiting for the proper part to arrive, You could simply feed the PAL-GTIA OSC clock (pin 28) to its PAL input (pin 16) with an inch of wire. Pin 16 is not connected in NTSC systems. And adjust the color pot for changed base shift (an so for the shifted pallete). After that your ony problem is different key-repeat rate (OS reads a reg in GTIA and assumes 50Hz or 60Hz VBL).

 

Hope that helps

[tjlazer]

So why not just use the PAL CHIP? I thought people got it to run PAL and NTSC software here in the states. I want to get one for my 1200XL. What all do you need for this this mod? I already have the 32-in-1 OS that has the PAL OS hack...

[antec]

GTIA is quite irrelevant for software issues. It just happens that the PAL color clock (4.43 MHz) does not divide so nicely into a 6502 main clock

(2.21 MHz would be out of spec for standard components of that time, 1.11 MHz would be lame, both would be quite off the 1.79 MHz benchmark).

So PAL GTIA has a separate input for additional 4.43MHz clocking signal, and PAL ATARI's have additional oscillators to provide it.

(Pin 16 is an input pin for PAL GTIA, do not let anyone tell you otherwise.)

ANTIC is way more important, as it controls the VBL rate, and shorter VBL-interrupts are the main issue in PAL/NTSC incompatibilities.

When people replace ANTIC's, they basically get a 50Hz-refresh NTSC machine, which seems to be just what is needed.

 

GTIA is an asynchronous chip (hard-wired delays inside), so playing with its timing it is a bit problematic. But I have replaced CTIA with PAL GTIA once, and it worked smoothly (400's OS does not read any registers from CTIA/GTIA ) .

 

What one could try is to take a PAL ANTIC, PAL GTIA, NTSC wiring, and overclock it by 5/4. If nothing catches fire, the video signal will be "62Hz PAL" , which modern TVs should accept, and 2.2MHz CPU. Anyone willing to try?

Edited December 15, 2007 by antec

[Rybags]

So, that would involve putting the PAL crystal in place of the standard NTSC one?

 

The RAM in newer machines will handle the higher speed just fine, since it has latencies much under what's needed.

 

Problem is, POKEY would be way out, so sound would be higher pitched, and a custom OS would be needed just so that you could boot a disk (assuming you could get the dividers needed for 19.2 k SIO).

[walter_J64bit]

LOL, I've just looked at My XEGS Motherboard, the GTIA is on a socket!

Edited December 16, 2007 by walter_J64bit