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Running PAL A8's at NTSC speed


Level42
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I know this has been discussed before and several ways have been suggested but I was wondering about this again.

 

I live in PAL territory and thus all but one of my A8's are PAL.

 

However, since I've played the older (cart) games on NTSC speed I really wouldn't want to play them at PAL speed again. But yet....I don't want to have NTSC only machines because of the more recent games and demos needing "standard" PAL or having PAL/NTSC detection.

 

My goal is to be able to play the old games (let's say pre 1986) at NTSC speed on a PAL machine. Nothing more. Of course I'd prefer the set-up to be switchable.

 

As monitor I use a Bang & Olufsen MX4000 TV which can display both PAL and NTSC composite and/or Y/C signals without problem.

 

I know there are two crystals in PAL machines but I don't know much about the details.

 

I did find this interesting little PCB from Adafruit which can be programmed to deliver any clock between 8kHz and 150Mhz. It can also provide 3 clock signals, all independent from each other:

 

https://learn.adafruit.com/adafruit-si5351-clock-generator-breakout/overview

 

The one thing I don't know for sure yet is if it can run stand-alone, the Adafruit people seem to say not, but the datasheet of the SI5351 says it has NVRAM for start-up so that's a bit unclear...

 

ANyway, if we can calculate the speed difference between NTSC and PAL games.....could we adjust one (or both) clock signals in a PAL machine to get exactly the right speed without getting display problems ?

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The quick/easy solution is just use an NTSC Antic.

Even though the main clock speeds are slightly different it's Antic more than anything that decides game speed since the framerate will be either just under 50 or 60.

By using NTSC Antic but leaving the rest along you'll still get the PAL 4.43 MHz colourburst so the monitor should work OK.

Some programs might have quirks since the GTIA reports as PAL. The key repeat rate will be annoyingly slow as well.

 

There's no easy way yet to switch between the 2 systems. If someone developed a dual system adaptor board. Or a modern day Antic and GTIA replacement with switching would be the way to go but it's probably not close.

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There's no easy way yet to switch between the 2 systems. If someone developed a dual system adaptor board. Or a modern day Antic and GTIA replacement with switching would be the way to go but it's probably not close.

 

 

A long-time dream of mine... Please, someone make it happen. Money is waiting. :)

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The quick/easy solution is just use an NTSC Antic.

 

Even though the main clock speeds are slightly different it's Antic more than anything that decides game speed.....

Really .....mmmm didn't realise that. Worth giving a try swapping the Antic from my NTSC 800XL.

 

Thing is......speed should be _exactly_ like NTSC gameplay for me....

 

So....are the crystals for the main part of the system equal on both NTSC and PAL machines ?

And......could we simulate the speed difference by only increasing the main clock frequency with the correct factor ?

Edited by Level42
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In the context of gaming accuracy the main clock doesn't really matter. The difference is so small that you'd not notice 59.94 FPS vs 59.92 FPS or whatever the resultant happened to be.

 

With the colour stuff - GTIA uses the master clock 3.59 MHz on NTSC to generate the colours but on PAL the colourburst has to come from a seperate crystal since it's at a 5:4 ratio, ie about 4.43 MHz.

 

In fact that 's probably the main difference between PAL and NTSC motherboards, the PAL GTIA has a seperate input pin for the clock used to generate colour where NTSC doesn't.

 

The colours generated by GTIA can be altered by the colour tuning pot. Whether a foreign GTIA can run on clocking for the other system and still generate the proper colours for either, I don't know. My suspicion is that the colours might be off a bit but probably not by a huge amount.

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I have tried a PAL CPU card in an NTSC 800. My monitor didn't like it. That would be the best of both worlds if we can get a good picture.

 

It works when you change the crystal to a PAL one.

 

NTSC: 3.57945 MHz - CO10177 or CO61090

PAL: 3.546894 MHz - CO16112 (standard on every PAL XL/XE)

 

The system clock crystal type must match the GTIA system (NTSC GTIA = NTSC system crystal) to get a coloured display. And when using PAL, the PAL color carrier circuit must also be present.

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I have all my Ataris imported from Argentina and there the pre-1990 machines are original NTSC converted to PAL-N 50hz. These system is a "Frankenstein" to fit the PAL system into american RF frequency. These machines uses PAL Antic and internally generates NTSC 50hz signal, and have a extra board containing the crystal and discrete circuitery to convert into PAL-N. The color palette are the same of european PAL, but in hi-res artifacting the colors are slighty different.

 

Because multi-system PAL-NTSC TV sets are common since the end of 80's in the Mercosur region these conversions became unnecesary, all video devices are sold in NTSC right.

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Thank you for the info, and Welcome to AtariAge. Would you happen to have photos or (better yet) schematics of those conversions?

 

I'd love to basically have an overclocked PAL 800 running at 50 FPS at the slightly higher 1.79 vs 1.77. Do you think anything like this is possible?

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That would slightly speed up the line rate. Though Atari's by default use a slightly slower line rate than analog broadcast standards.

 

NTSC 228 vs 227.5

PAL 285 vs 283.75

 

How TVs would cope with that, unknown. The older analog controlled CRTs seem to be fairly versatile, the main things of importance is the colourburst frequency matches and the overall frame rate is close to the home standard.

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Couldn't we make a switchable GTIA and ANTIC ?

 

It will require a lot of switches but I guess address and datalines can be simply "piggybacked" ?

 

There are analog switches in SMD packages so you could fit a lot of them on one board.

 

One mechanical switch would control all those analog switches at once. There's no need for "on the fly" switching I guess. The crystal would need switching too, I guess that should be done though a mechanical switch so we'd need a DPDT.

 

I don't know if analog switches in IC format will have any influence on the signals going in and out of the ANTIC and GTIA.

 

It's a basic idea....but as long no-one has tried it.....

Edited by Level42
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Maybe Dropcheck would make up an NTSC GTIA conversion board like she has for NTSC-to-PAL conversion. I converted my 1200XL to PAL with it. Comes with the special board that sits in the GTIA socket, a PAL chrystal and then you just drop in PAL GTIA on the board and put a PAL ANTIC right in the ANTIC socket. Walla! A PAL computer. It seems to me the exact same, mirrored, conversion could be done to turn PAL-to-NTSC.

Edited by Gunstar
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