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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: madgrizzle on August 10, 2017, 01:26:17 AM
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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.
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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.
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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 (http://www.ebay.com/itm/Amiga-2000-CDTV-Megachip-Chip-Ram-Adapter-/322628722919?hash=item4b1e2ba0e7:g:EcwAAOSwRgJXgWan)) 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.
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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).
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bottom line with all the technical talk is get an NTSC megachip for ntsc amiga!
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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.
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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.
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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.
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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.
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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.
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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?
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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.
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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.
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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.
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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:
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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)
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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)
:roflmao:
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If you are incredibly fortunate, you might find you already have an 8372AB fitted or 8372B.
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.
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?
Yes! No Agnus has the capability to auto-detect the master oscillator frequency! So designing a "plug and play" universal megachip isn't possible.
If it could autodetect whether the motherboard is equipped with a 28.63636 MHz (NTSC) oscillator or a 28.37516 MHz (PAL) one, it could of course also be designed to automatically adjust its bootup timings accordingly. But this would require an independent internal clock inside the Agnus and extra comparator circuitry, which is an unnecessary complexity.
So when you set an Agnus to PAL timings, you're simply more or less just telling it "look, I assure you that the master clock is 28.37516 MHz and I want PAL timings, so each scanline will be 1816 ticks long, even fields will be 313 scanlines high and odd fields will be 312 scanlines high, VBLANK time will be 25/24 scanlines and I want hardware enables/stops at ticks #X and #Y for each scanline"
Similarly, when you set an Agnus to NTSC timings, you're simply telling it "there's a 28.63636 MHz master clock so I want NTSC timings, so even fields will be 263 scanlines high and odd fields will be 262 scanlines high and scanline length will alternate between 1816 and 1824 ticks etc etc"
The above instruction set for example correctly produces the NTSC interlaced field pattern:
-first field (#0) is even, so it has 313 scanlines (odd number), so it begins and ends with a short line (1816)
-second field (#1) is odd, so it has 312 scanlines (even number), it begins with a long line (as field #0 ended with a short line) and thus ends with a short line
-third field (#2) is even, so it has 313 scanlines (odd number), it begins with a long line (as field #1 ended with a short line) and thus ends with a long line
-fourth field (#3) is odd, so it has 312 scanlines (even number), it begins with a short line (as field #2 ended with a long line) and thus ends with a long line
... and the sequence repeats, i.e. fifth field (#4) is identical to #0 etc, so we get the periodic sequence:
- long field ending on short line
- short field ending on short line
- long field ending on long line
- short field ending on long line
Given all that, it's impossible for an Agnus to 'refuse' to be set to PAL timings if an NTSC oscillator is presence, and vice versa.
This leads to the 1% faster "nearly PAL" (when oscillator = NTSC but Agnus timings are PAL)
and 1% slower "nearly NTSC" (when oscillator = PAL but Agnus timings are NTSC) timings, which may well be video-hardware incompatible.
But these are the only video-illegal modes.
Any NTSC video hardware finding an Amiga with an NTSC oscillator and an NTSC-timed Agnus (regardless if it was set via jumpers or soft-switched via the KS 3.x menu) will work just fine.
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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.
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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.
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I hear you Pat and appreciate your comments. I probably was too quick to pull the trigger, but it is what it is. The nice thing about the VA2000/CX is that its an fpga and the developer is still active. I'd be more concerned if I had a legacy graphics card, but right now, I'm hopeful with the parameters that can be set for the VA2000/CX that I can get it to work. There are setting for mode (resolution), hsize, vsize, hoffset and voffset..
Is it correct to say that the megachip itself (not the chip, but the board) is the same regardless of being PAL or NTSC? So if I find a NTSC Agnus I can pop it in and get a working NTSC megachip?
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I hear you Pat and appreciate your comments. I probably was too quick to pull the trigger, but it is what it is. The nice thing about the VA2000/CX is that its an fpga and the developer is still active. I'd be more concerned if I had a legacy graphics card, but right now, I'm hopeful with the parameters that can be set for the VA2000/CX that I can get it to work. There are setting for mode (resolution), hsize, vsize, hoffset and voffset..
Is it correct to say that the megachip itself (not the chip, but the board) is the same regardless of being PAL or NTSC? So if I find a NTSC Agnus I can pop it in and get a working NTSC megachip?
Yes the board is the same and will happily take as a drop-in replacement the other Agnus.
Matching pairs are:
390544-01 (PAL) and 390544-02 (NTSC) , non Vbb, 2 MB 8375 Agnus
318069-10 (PAL) and 318069-11 (NTSC), Vbb, 2 MB 8375 Agnus
My very own Megachip was originally equipped with a 390544-02 NTSC Agnus (bought it from the US). Used it in soft-switch mode (*) on my otherwise PAL A500 for a while, then replaced it with a 318069-10 one without any issues and eventually with the "proper" 390544-01 one just cause I found one cheap.
(*) Of course, soft-switching after boot up is not recommended as specific software may already have determined the mode and expect it remains unchanged. But if you stick to soft-switching via the early bootup menu, it'll be as good as having an NTSC Agnus.
I doubt the VA2000/CX cares much about that stuff, anyway. Seems to me it just keeps sampling the RGB info on the videoslot and sends it "resized" into a VA2000 videobuffer for display under some native mode, essentially acting as a scandoubler.
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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?
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Not if he's got a skinny Agnus A2000.
board = the megachip board, not the A2000 motherboard
Is it correct to say that the megachip itself (not the chip, but the board) is the same regardless of being PAL or NTSC? So if I find a NTSC Agnus I can pop it in and get a working NTSC megachip?
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Just installed megachip. Booted up to workbench with no issues. After boot, Amiga Workbench shows 1,912,888 graphics mem. I was able to run Cannonfodder, which requires 2 MB of chip ram.
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I was able to run Cannonfodder, which requires 2 MB of chip ram.
Always a good test. I seem to recall buying a Megachip years ago for my A500 for just the same reason. :lol:
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To add some additional information to the topic, as I have been working on getting a 3000 going, I haven't done anything with my 2000. I went ahead and connected the output of the 23-pin video to a GBS8220 to see what the PAL megachip would do and though it took some tweaking, the video works well with the workbench. Whatever incompatibility there might be due to a PAL agnus inside an NTSC amiga is handled by the GBS. I also tried a game on it (Defenders of the Crown) and it worked as well. However, you cannot set a tooltype of NTSC for it. I assume if there is no tooltype, it defaults to PAL and that seems to work.
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Cannonfodder ? That ran on my 1MB Chip mem A2000 in the 90s ?
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Cannonfodder ? That ran on my 1MB Chip mem A2000 in the 90s ?
With WHDLoad it needs 1.5MB, AFAIR.
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I've got a PAL megachip in my NTSC A2000...no issues whatsoever. I also have a PAL megachip in an NTSC A500...again, no issues.
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What do you have it connected to? Are you going direct to a monitor or something else?
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On the 500, I have an Indivision ECS. On the a2000, I have it passing out through an SCART to one of those HDMI upscalers.