CPU boards, and swapping PAL/NTSC..

[andym00]

Just wondering if I was to obtain a couple of NTSC CPU boards from Best if that's all I'd need to convert my 400 & 800 from PAL to NTSC ?

 

Is it really that simple ? Just pop it in ? Or are there other clock shenanigans to take into account that'll bite me ?

[Rybags]

Not quite... but it would be a near-enough solution, exceptions listed below.

Personally, I'd do an XL or XE - the advantage there is that the OS on those is universal and better able to cope with the differences.

 

PAL machines also have the ~ 4.3 MHz crystal needed for the proper PAL colour carrier frequency.

 

You can do a quick & dirty NTSC machine by just putting an NTSC Antic into a PAL machine. End result is it'll be slightly slower than a real NTSC machine due to 1.78 vs 1.79 MHz speed. I did that on one of my XEGS machines. IIRC it works fine on the 1084S monitor I have that otherwise doesn't work properly with native NTSC signals.

 

Next step up is NTSC GTIA - for whatever reason, the GTIA actually holds the PAL hardware register that software can interrogate to determine what system you're on. In most cases it won't matter but in some it will.

 

As for the full-blown way, ie having NTSC GTIA and Antic and master clock but using the PAL colourburst crystal feeding the proper signal into GTIA... I don't even know if that's possible. PAL GTIAs put the phase delay onto that extra signal on a seperate input pin. Not sure if NTSC machines also do that, or merely use a "copy" of the master clock.

Edited December 27, 2010 by Rybags

[andym00]

Not quite... but it would be a near-enough solution, exceptions listed below.

Personally, I'd do an XL or XE - the advantage there is that the OS on those is universal and better able to cope with the differences.

 

PAL machines also have the ~ 4.3 MHz crystal needed for the proper PAL colour carrier frequency.

 

You can do a quick & dirty NTSC machine by just putting an NTSC Antic into a PAL machine. End result is it'll be slightly slower than a real NTSC machine due to 1.78 vs 1.79 MHz speed. I did that on one of my XEGS machines. IIRC it works fine on the 1084S monitor I have that otherwise doesn't work properly with native NTSC signals.

 

Next step up is NTSC GTIA - for whatever reason, the GTIA actually holds the PAL hardware register that software can interrogate to determine what system you're on. In most cases it won't matter but in some it will.

 

As for the full-blown way, ie having NTSC GTIA and Antic and master clock but using the PAL colourburst crystal feeding the proper signal into GTIA... I don't even know if that's possible. PAL GTIAs put the phase delay onto that extra signal on a seperate input pin. Not sure if NTSC machines also do that, or merely use a "copy" of the master clock.

 

Sounds promising and worth a quick try at least.. It's only for testing my own stuff on, and it'd be purely an occasional testing thing, rather than shipping a 400 or 800 from the states that's likely to arrive in more pieces than it departed in..

 

The clock rate will be close enough, and being slightly slower is better than slightly faster.. As long as it'll display on one of the commodore monitors I've got, then no worries..

 

I assume the 400/800 ROMs won't have a problem with this though ? I mean they check the region and handle things somewhat correctly if it finds an NTSC Antic ?

 

All excited now

[Rybags]

400/800 ROMs are hard-coded for whatever region.

 

The first thing you'd notice is the key repeat rate changes. Actually on a PAL system changed to NTSC that is a good thing because it speeds up. On the other hand an NTSC OS on PAL hardware means an annoying slowdown.

 

Cassette loads will probably fail, but <who cares>.

 

The clock speed difference like you said - it won't be noticable, the frame rate will be slightly slower but then again, they weren't true PAL/NTSC rates in the first place due to the missing half scanline.

[andym00]

I don't think I'll be doing anything other than booting it from a flash cart, so the keyboard and cassette IO aren't important to me..

As long as it'll fire up a cart I'll be a happy bunny

 

[Rybags]

Just go for it then.

 

Old TV sets will likely not like it and just show B&W, but the newer gear and most monitors should be fine.

[pavros]

Hi,

 

Cassette IO should be fine. Some years ago I replaced 14.18MHz oscillator in my 130XE with 16MHz one just to check if it can run on 2MHz CPU clock. I worked perfectly and noticable faster which I could check listening to some musics (TV sync was broken of course). Loading from cassette worked fine for standard 600 baud as well as for 6000 (Blizzard Turbo system, common in Poland). Seems like POKEY has its built-in internal clock 1.78MHz which is not dependent on any external signals.

[Rybags]

There's no internal fixed clock... and it's been used in various arcade applications from ~ 1.2 to 1.79 MHz, and also at ~ 500 Khz by someone doing a standalone audio project. Resultant audio frequencies will always vary according to what base clock you're feeding into it.

 

Pokey is tolerant to some variation in serial input speed.

The docs say +-5% for unclocked Serin data, but maybe that's a lowball figure.

[pavros]

OK. Maybe it was POKEY's tolerance which allowed correct cassette IO with 2MHz clock but in that case it would be like at least +11%. Anyway, difference between 1.78 and 1.79 should not matter at all. Which POKEY pin is base clock input BTW?

[Rybags]

http://www.atarimax.com/jindroush.atari.org/achpokey.html

 

That should be Pin 7.

[frogstar_robot]

There's no internal fixed clock... and it's been used in various arcade applications from ~ 1.2 to 1.79 MHz, and also at ~ 500 Khz by someone doing a standalone audio project. Resultant audio frequencies will always vary according to what base clock you're feeding into it.

 

Pokey is tolerant to some variation in serial input speed.

The docs say +-5% for unclocked Serin data, but maybe that's a lowball figure.

 

A variable clock could be an interesting addition to a dual POKEY mod. The original POKEY would have to be left alone because of the other chores it does but the ability to vary the second POKEY's clock from software would at the very least offer possibilities for accurate tuning not to mention the sounds you could get if it can tolerate having it's clock swept through a range.

[Rybags]

Problem there though is you'd need it running synchronous to the CPU anytime doing register accesses... or need to have a bridging interface that handles the transfers at the different clock rates.

[ijor]

OK. Maybe it was POKEY's tolerance which allowed correct cassette IO with 2MHz clock but in that case it would be like at least +11%.

 

This has (almost) nothing to do with the serial pokey tolerance (which btw, it is not specific to Pokey, but it is intrinsic to serial async transmission).

 

Tape SIO is unlike, and different in many ways, than any other "regular" SIO. One of the differences is that standard tape blocks are recorded with a header consisting of two bytes with alternates one and zero bits. When reading the tape, this header is read without using Pokey serial engine (there is no need because the bit pattern is known), and it is timed. The timed value of this header, translated with a table, is used to configure Pokey serial frequency for the rest of the block. An 11% wouldn't be a problem (not in this regard).

[Rybags]

Forgot to take that into account... the Frame/Vcount timing is sped up so therefore the relationship between those and Pokey AUDF intervals would still be the same.

 

So long as the bit rate of the tape hadn't drifted outside the range the tables cover, it should still work normally.

[pavros]

Ah, yes! I also forgot about tape rate detection. As far as I remeber it's two bytes $55,$55 preceding each block of data and AUDFs are adjusted according to detected rate. Yes, this must be an explanation why tape IO was still working. Thanks guys.

[Thorsten Günther]

Just wondering if I was to obtain a couple of NTSC CPU boards from Best if that's all I'd need to convert my 400 & 800 from PAL to NTSC ?

 

Is it really that simple ? Just pop it in ? Or are there other clock shenanigans to take into account that'll bite me ?

 

May I suggest a much simpler method?

 

Sell the PAL 800 on eBay (UK e.g., but you may get even better prices for these machines are even rarer here - Germany) and buy an NTSC one on eBay USA. 800s are pretty common on the western side of the pond and quite rare on the eastern side due to the high price (a friend of mine had his parents buy him an 800 and 810 - they paid about DM 5,000 (that's more than EUR 2,500).

 

Thorsten

[Almost Rice]

May I suggest a much simpler method?

 

Sell the PAL 800 on eBay (UK e.g., but you may get even better prices for these machines are even rarer here - Germany) and buy an NTSC one on eBay USA. 800s are pretty common on the western side of the pond and quite rare on the eastern side due to the high price (a friend of mine had his parents buy him an 800 and 810 - they paid about DM 5,000 (that's more than EUR 2,500).

 

I agree with Thorsten. There are additional reasons. Modern monitors are not so forgiving with these mixed machines. Most will not display the video and at best a B/W screen. It is better to get an NTSC machine if you want NTSC and a PAL machine for PAL. I learned it the hard way and bought PAL systems to use if I want to run PAL only software.

[Rybags]

NTSC 4.43 is actually a psuedo-standard and plenty of gear out there will handle it.

 

IMO the cheapest and easiest way by far would be to just get an NTSC Antic and put it in the existing board.

[andym00]

May I suggest a much simpler method?

 

Sell the PAL 800 on eBay (UK e.g., but you may get even better prices for these machines are even rarer here - Germany) and buy an NTSC one on eBay USA. 800s are pretty common on the western side of the pond and quite rare on the eastern side due to the high price (a friend of mine had his parents buy him an 800 and 810 - they paid about DM 5,000 (that's more than EUR 2,500).

 

The PAL 800s are staying, I like them too much, and the NTSC requirement is something that'll be needed not too often..m Much as that'd be the simpler solution buying an NTSC 800, shipping is not going to be trivial.. I did think of this first actually, but then stumbled across the CPU boards on Best.. When I enquired about the cost of shipping their NTSC 800s to the UK, the answer was not promising due to the weight and I quote "Because of the very heavy nature of the original Atari 800 computers Andy, they are not cost effective to ship to the UK".. Although the price is good, (~80UKP), shipping is going to be bonkers..

 

For now, and because I want to keep an 800 as a PAL machine, I'll grab a couple of CPU boards and do the dirty conversion like this, and keep an eye out for an NTSC 800 turning up on eBay UK or somewhere closer..

[andym00]

NTSC 4.43 is actually a psuedo-standard and plenty of gear out there will handle it.

 

IMO the cheapest and easiest way by far would be to just get an NTSC Antic and put it in the existing board.

 

But I'm crap with a soldering iron so the $15 cost of the CPU board saves any innocent computers getting injured in the process..

[andym00]

I agree with Thorsten. There are additional reasons. Modern monitors are not so forgiving with these mixed machines. Most will not display the video and at best a B/W screen. It is better to get an NTSC machine if you want NTSC and a PAL machine for PAL. I learned it the hard way and bought PAL systems to use if I want to run PAL only software.

 

 

Between my 1701, 1702 & 1084 I think there's not going to be a problem displaying it..

I do agree that having an NTSC 800 would be the best solution though, it's just a question of finding one at the right price with shipping not being insane.. For now I'll take the CPU board change option as an interim solution, and just keep an eye out for NTSC 800s..

[Rybags]

Fair chance the 800 is all socketed... been a while since I had my 400 apart, can't remember if the CPU board was or not.

[Almost Rice]

I agree with Thorsten. There are additional reasons. Modern monitors are not so forgiving with these mixed machines. Most will not display the video and at best a B/W screen. It is better to get an NTSC machine if you want NTSC and a PAL machine for PAL. I learned it the hard way and bought PAL systems to use if I want to run PAL only software.

 

 

Between my 1701, 1702 & 1084 I think there's not going to be a problem displaying it..

I do agree that having an NTSC 800 would be the best solution though, it's just a question of finding one at the right price with shipping not being insane.. For now I'll take the CPU board change option as an interim solution, and just keep an eye out for NTSC 800s..

 

On a older monitor, it is more likely you manually select NTSC or PAL so it is not a problem. Newer LCD monitors that I have used do no like the NTSC systems with PAL ANTIC or PAL systems with NTSC ANTIC, because they autodetect PAL or NTSC if the signal is 50Hz or 60Hz. I get either a rolling picture or at best a black and white picture.

[Thorsten Günther]

On a older monitor, it is more likely you manually select NTSC or PAL so it is not a problem. Newer LCD monitors that I have used do no like the NTSC systems with PAL ANTIC or PAL systems with NTSC ANTIC, because they autodetect PAL or NTSC if the signal is 50Hz or 60Hz. I get either a rolling picture or at best a black and white picture.

 

Fully acknowledged, this is a common problem regarding any non-CRT based TV sets. One should constantly keep in mind that LCD and Plasma TVs are in fact computers embedded in a TV casing, and they are unlikely to accept PAL60 or NTSC with 50Hz - it simply didn't cross the programmers' mind that such a signal could even exist. I encountered the same problem with PAL60 ROMs on the VCS2600 (thankfully, I tried it with a Harmony cartridge).

 

Thorsten

[mimo]

800 should be fully socket-ed, and if you ask around here I'm sure you will get an ANTIC chip for less than $15

as for converting a 400, you would have to get the rf monitor as well, and it is an awful lot harder to use an NTSC RF signal in the UK compared with composite or s-video.