PAL vs NTSC Megachip

[madgrizzle]

What's the difference between a PAL and NTSC Megachip (besides one being PAL and the other NTSC).  I'm looking to increase the chip RAM in my Amiga 2000 and, unless I'm wrong, NTSC Megachip is fairly rare (and therefore expensive when they do come available.. I don't watch amibay 24/7 to express interest if one did show up there).  PAL Megachips, however, seem less rare.  Since I use a graphics card (VA2000/CX) and if there is no difference in motherboards, what is stopping me from installing a PAL Megachip?  I know the VA2000/CX works with PAL.

[Matt_H]

Gotta use the version that corresponds to your motherboard, I'm afraid. I don't know all of the technical details, but there are very subtle differences between the PAL and NTSC versions of Agnus (the 2MB Agnus is the other main component of a Megachip) as well as the PAL and NTSC motherboards, so you need both parts to match.

[BLTCON0]

What's the difference between a PAL and NTSC Megachip (besides one being PAL and the other NTSC).

First of all, there's no PAL / NTSC when it comes to the A2000, since it doesn't have an RF modulator and only produces a monochrome composite signal (PAL and NTSC include specifications for colour and audio subcarrier signals).
So by PAL / NTSC we'll simply refer to PAL-timed and NTSC-timed, as the only thing that remains is each standard's timing specifications.

The only difference is the Agnus. A "PAL" megachip has a PAL-timed Agnus and an "NTSC" one an NTSC-timed Agnus.

But this also implies that each version must be matched by the proper oscillator on the motherboard:
28.37516 MHz for "PAL" and 28.63636 MHz for "NTSC".

So if you can only get a PAL megachip, you have two options:

1. Leave it running in PAL mode (which might even be desirable for many apps and games), mindful that it'll be a slightly "overclocked" PAL since the oscillator is a bit faster (by about 1%). It'll generally not matter though and will be hardly noticeable.

2. Soft-switch the Agnus to NTSC timings after the system has booted up (all megachips support that), using a suitable utility (degrader etc) or even KS 3.1's own bootup menu. This will result in a perfectly NTSC-timed system.


Most megachips come with the 8375 Agnus, in its PAL or NTSC variant respectively, and only support software switching between PAL/NTSC timings.
But a rare minority use the original 8372B 2 MB Agnus, which can be configured to boot in either PAL or NTSC timings, selectable via pin41 (grounded = NTSC, floating or high = PAL). So these megachips are "the best" but on the downside they're ultra rare and typically considerably pricier.

 I'm looking to increase the chip RAM in my Amiga 2000 and, unless I'm wrong, NTSC Megachip is fairly rare (and therefore expensive when they do come available.. I don't watch amibay 24/7 to express interest if one did show up there).  PAL Megachips, however, seem less rare.

A few years ago it was the other way round. Anyway, I'd say just buy the PAL one (one on sale here) and if need be, you can always ask around for the NTSC-equivalent Agnus and replace the PAL one. Or you may find that soft-switching when required is not a very big nuisance after all.

 Since I use a graphics card (VA2000/CX) and if there is no difference in motherboards, what is stopping me from installing a PAL Megachip?  I know the VA2000/CX works with PAL.

Nothing stops you, go for it.

[BLTCON0]

Gotta use the version that corresponds to your motherboard, I'm afraid.

Not really, they work fine. The only side-effect is that by running a PAL Agnus on an NTSC oscillator you get ~1% faster PAL timings. If he soft-switches to NTSC, it's 100% the same as having an NTSC Agnus, so then Agnus and oscillator match and he gets perfect NTSC timings.
Conversely, by running an NTSC Agnus on a PAL oscillator, you get ~1% slower NTSC timings, but perfect PAL-timings when soft-switching the Agnus to PAL.

(The above 1% variances in each case would only likely matter for stuff like video work).

 I don't know all of the technical details, but there are very subtle differences between the PAL and NTSC versions of Agnus (the 2MB Agnus is the other main component of a Megachip) as well as the PAL and NTSC motherboards, so you need both parts to match.

Ideally yes, to produce the expected timings.

The Agnus doesn't actually "know" if it's in a PAL or NTSC system.
A PAL (or PAL-configured) Agnus will simply assume the oscillator is the correct PAL 28.37516 MHz one. Similarly, an NTSC (or NTSC-configured) Agnus will simply assume the oscillator is the correct NTSC 28.63636 one, and adjust timings accordingly.

E.g. in PAL mode the time-length of each horizontal scanline will be 1816 oscillator 'ticks', while in NTSC mode it will be 1820 ticks.
The Agnus has no way of knowing if the input frequency is indeed PAL-correct or NTSC-correct, so a PAL configured Agnus will still produce 1816-tick-long lines even if the oscillator is an NTSC one.
Similarly, an NTSC configured Agnus will still produce 1820-tick-long lines even if the oscillator is a PAL one (actually it'll be alternating 1816- and 1824-long lines as 1820 isn't divisible by 8, but that's of little interest here).

[magnetic]

bottom line with all the technical talk is get an NTSC megachip for ntsc amiga!

[madgrizzle]

I wonder if the difference in timing will throw-off the VA2000/CX.. Regardless, soft-switching doesn't likely to seem to be much of an issue.

[BLTCON0]

bottom line with all the technical talk is get an NTSC megachip for ntsc amiga!

Quite the opposite - the tech talk establishes he can use a "PAL" megachip and soft-switching the Agnus still have an 100% accurate "NTSC" system.

[Pat the Cat]

Quite the opposite - the tech talk establishes he can use a "PAL" megachip and soft-switching the Agnus still have an 100% accurate "NTSC" system.

This is correct from a software compatibility point of view.

It is not correct from a video expansion hardware compatibility point of view.

If you want to use external video hardware that is NTSC based, stick with an NTSC Amiga. It will save you SO much messing about going in circles.

Likewise, PAL external video hardware is designed to work with PAL specifications, and PAL itself differs subtly from country to country.

Amgias were designed to output to both kinds of monitors, but when it comes to things like genlocks, video digitizers, frame buffers etc, the 2 different crystal types fitted inside the 2 different styles of Amiga (and also differently wired video encoders on some Amigas) mean they just don't work with the "other" system.

Things get even worse when you are talking about video card expansions on A2000/A3000/A4000. It's a rats nest of complexity.

[BLTCON0]

This is correct from a software compatibility point of view.

And also from a hardware compatibility point of view.

It is not correct from a video expansion hardware compatibility point of view.

I addressed that in my 2nd post, but only PAL-timed video work would be affected.

If you want to use external video hardware that is NTSC based, stick with an NTSC Amiga. It will save you SO much messing about going in circles.

An Amiga 2000 with the correct 28.63636 MHz oscillator AND an Agnus running in NTSC timings *IS* an NTSC Amiga 2000, no matter if the Agnus defaulted in NTSC timings or was soft-switched into them.

Likewise, PAL external video hardware is designed to work with PAL specifications, and PAL itself differs subtly from country to country.

It differs with respect to the colour and audio subcarriers, none of which are at play inside an Amiga 500/2000. These are issues for colour composite outputs and RF modulators.
Under RGB the terms PAL and NTSC are reduced to PAL-timed and NTSC-timed, nothing more.

Amgias were designed to output to both kinds of monitors, but when it comes to things like genlocks, video digitizers, frame buffers etc, the 2 different crystal types fitted inside the 2 different styles of Amiga (and also differently wired video encoders on some Amigas) mean they just don't work with the "other" system.

Things get even worse when you are talking about video card expansions on A2000/A3000/A4000. It's a rats nest of complexity.

What do you mean the two different crystal types? In an Amiga there's only one crystal, inside the oscillator can. The Agnus has no crystal/oscillator of its own, it produces the system timings by dividing/shifting/inverting the single master clock.
So since the important thing (the oscillator) in this case is already of the correct NTSC type (28.63636 MHz), the only remaining factor to match is the Agnus. So if set to NTSC timings, all's good. It's really that simple.

Let alone that in some applications the master clock is externally provided and Agnus ignores the motherboard oscillator which becomes irrelevant in this case - so the only requirement is that the Agnus timings match the external source's.

[Pat the Cat]

But the master clock oscillators run at different speeds in NTSC and PAL Amigas.

While the chips are identical, the basic ticks run at different speeds.

Re: A1200 Motherboard NTSC or PAL?

Two easy ways.

1. Look at the markings on the crystal oscillator. It's just to the left of the ROMs. If it says 28.63636 it's a NTSC motherboard. If it says 28.37516, it's PAL.

2. If there is a crystal just to the right of the IDE connector, it's PAL. If there isn't one there, it's NTSC.

[/B]


IIRC an Agnus with pin 41 masked defaults to PAL timings. An important thing to remember when removing and reinserting Agnus chips (the mask might fall off between reinsertion).

EDIT: Right BLTCON0, you had all that covered anyway. But I stand by my original point - there's a big difference between "compatible with NTSC or PAL video hardware" and "compatible with running software at PAL or NTSC speeds". Which was actually what the orginal poster was asking for;-

Since I use a graphics card (VA2000/CX) and if there is no difference in motherboards, what is stopping me from installing a PAL Megachip? I know the VA2000/CX works with PAL.

Even if the VA2000/CX does work with a PAL megachip, external NTSC equipment will not work, even if the machine is soft switched into NTSC mode (because then the megachip has issues switching an 8375 from PAL to NTSC, which is why there are 2 versions).

If this isn't accurate, then please tell me why there are 2 different versions of the megachip, PAL and NTSC. Just default timing settings?

[UberFreak]

There's a guy on Amibay (Tuxbar81) who designed a replacement for the Megachip for A500/2000, he's selling them assembled or as kits.
Two batches have been sold already, pre-orders for the 3rd are currently open.

Look here:
http://www.amibay.com/showthread.php?92591-Project-of-Megachip-for-Amiga

What's the difference between a PAL and NTSC Megachip (besides one being PAL and the other NTSC).  I'm looking to increase the chip RAM in my Amiga 2000 and, unless I'm wrong, NTSC Megachip is fairly rare (and therefore expensive when they do come available.. I don't watch amibay 24/7 to express interest if one did show up there).  PAL Megachips, however, seem less rare.  Since I use a graphics card (VA2000/CX) and if there is no difference in motherboards, what is stopping me from installing a PAL Megachip?  I know the VA2000/CX works with PAL.

[Pat the Cat]

There's a guy on Amibay (Tuxbar81) who designed a replacement for the Megachip for A500/2000, he's selling them assembled or as kits.
Two batches have been sold already, pre-orders for the 3rd are currently open.

Look here:
http://www.amibay.com/showthread.php?92591-Project-of-Megachip-for-Amiga

Uh... not suitable for A2000 according to the link.

Onto which Amiga this board works?

The design has been made of the A500 rev6 motherboard.
The electronic design works onto the A2000 but the geometry design is not adapted for this computer.
The routing for the A2000 version will be made soon.

I suggest madgrizzle checks what Agnus and motherboard revision they have, and look for an alternative method of upgrading chip RAM. Or, wait for tuxbar to do a version that will fit an A2000.

If you are incredibly fortunate, you might find you already have an 8372AB fitted or 8372B. Which are the Agnus types from an A3000, 2MB chip RAM OK. Replace the RAM chips already fitted and it's good to go. More likely it is an earlier Agnus. But check and post and maybe you can get some further advice.

Agnus chip types to give you some idea of what the limits are of each;-

https://en.wikipedia.org/wiki/MOS_Technology_Agnus

If you want a utility that will tell you without taking the machine apart (not motherboard, but at least Agnus type);-

http://aminet.net/package/util/moni/SysInfo
 
 Must admit, I'd just reach for the screwdriver rather than trust software. Yes, I know, I trust me. Not software.

[madgrizzle]

Even if the VA2000/CX does work with a PAL megachip, external NTSC equipment will not work, even if the machine is soft switched into NTSC mode

Ah, now I think I understand.. So even if the VA2000/CX can output a signal over HDMI, the HDMI monitor set for NTSC won't be able to display it?  When you talked about external equipment, I thought you were talking about things like genlocks and such which I don't use.

Well, anyway, we'll find out since I already bought the thing.  Who knows, maybe some of the settings of the VA2000CX can get tweaked.  Worst case scenario we'll put the question to rest and I either find an NTSC Agnus (right?) or just put it all up for sale for someone with a PAL Amiga.

[Oldsmobile_Mike]

Well, anyway, we'll find out since I already bought the thing

Maybe I missed the point of this thread, but assuming you have a monitor or display device that supports both NTSC and PAL, what's the issue?  (assuming you're not using a genlock or something, as someone stated above).  For Workbench and productivity software it won't matter, just select whatever screenmode you want, and for games you can select either PAL or NTSC with WHDLoad/Degrader/etc.  I don't think anyone's too likely to notice that 1% speed difference mentioned above.

Or is the question will a NTSC motherboard + NTSC VA2000/CX work with a PAL Megachip?  Guess, like you said, we'll find out!  



##SMDH, I can't believe we're still having issues with NTSC vs. PAL in 2017, lol. :laughing:

[madgrizzle]

Maybe I missed the point of this thread, but assuming you have a monitor or display device that supports both NTSC and PAL, what's the issue?

Heck, I thought I understood this stuff until this morning.  Its a Dell (I think S2240L) with VGA and HDMI.. and I use HDMI with the VA2000/CX.. Isn't PAL and NTSC an analog thing?

For Workbench and productivity software it won't matter, just select whatever screenmode you want, and for games you can select either PAL or NTSC with WHDLoad/Degrader/etc.

Learning something new every day about my Amiga (didn't know about the WHDLoad tooltype).  Wish I hadn't taken a 25 year hiatus.

Or is the question will a NTSC motherboard + NTSC VA2000/CX work with a PAL Megachip?  Guess, like you said, we'll find out!  

AFAIK, there's no NTSC or PAL variety of VA2000/CX.. certainly didn't have to pick an option when I ordered it.

##SMDH, I can't believe we're still having issues with NTSC vs. PAL in 2017, lol. :laughing:

Hadn't heard of SMDH before.. when I googled it I got "Seriously Degraded Modem Hours"... which I thought was funny considering the era of the computers (I googled again and got the real definition)