PAL vs NTSC Megachip

[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.

[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?

[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.

[Pat the Cat]

The 8372AB is the 8372B, it's just the circuitry of the 8372B inside the packaging of the 8372A, so they separately suffixed a standalone "B" to signify it's a 8372B.

However, it's impossible to encounter such an Agnus in a production A2000. The 8372(A)B Agnus offers a single RAS line while the RAM design of the A2000 requires 2 RAS lines from the Agnus.
On the A3000, they solve this by recreating the separate RAS lines by combining the information from the RAS line and the two highest order address bits. But such circuitry doesn't exist in the A2000.

(scratches head, checks pin outs from link).

Correct. However, it is STILL worth checking to see what actual Agnus is fitted already, and whether or not there are any board modifications, and also what revision of motherboard is actually in use.

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?

Yes! No Agnus has the capability to auto-detect the master oscillator frequency! So designing a "plug and play" universal megachip isn't possible.

OK. So this particular Amiga will ALWAYS default to PAL and start up in that video mode. Unless madgrizzle wants to fit a switch that lets them start up in either PAL or NTSC.

...
The above instruction set for example correctly produces the NTSC interlaced field pattern:...

Bottom line is, after modifcation with the listed Megachip version (PAL) this particular A2000 might not work correctly with external expansions that demand a correctly timed interlaced NTSC signal. IE, external video expansions. OR graphics slot expansions, because essentially the graphics slot on an Amiga is the external set of connector pins with a few extra control pin signals.

Whether or not madgrizzle gets a working HDMI signal that they can use with their monitor... Will depend on the HDMI adaptors connection and operation.

I don't fancy your chances madgrizzle, but you've taken the plunge already, and it might just work fine.

Or it might not. Whether or not you need to change your display is pretty much in the hands of chance right now. You might need to fit a switch to get the Megachip 2000 to choose NTSC or PAL at startup, that doesn't seem like too much of a big deal to me.

It's just a LOT of people have had issues trying to get decent HDMI output from an Amiga, and adding a chip RAM expansion which defaults to the "opposite" video mode of the built in crystal is just asking for extra trouble. In my opinion.

[Pat the Cat]

Yes the board is the same and will happily take as a drop-in replacement the other Agnus.

Not if he's got a skinny Agnus A2000.
 
 I don't think madgrizzle has, seem to recall him mentioning a motherboard upgrade, but the thing is, people do sometimes search for existing answers, and for such people, buying a Megachip 2000 upgrade isn't an option.
 
 Kiss kiss. Keep It Stupidly Simple?