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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: orb85750 on December 03, 2010, 05:26:47 PM
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OK, I know that OS3.0/3.1 can switch between PAL and NTSC at boot-up. But is it simply the kickstart ROM that determines which way it boots by default? Or is there any other hardware/software side to it? In other words, can I make a machine NTSC by exchanging the kickstart with an NTSC ROM?
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AFAIK It's determined by the Agnus/Alice custom chip version.
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Changing the KS Roms won't do it, it's all down to slightly different motherboards, sorry... :(
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Changing the KS Roms won't do it, it's all down to slightly different motherboards, sorry... :(
Just a crystal, tv modulator and some other discrete things. It's quite trivial to convert Commodore computers from one standard to another.
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Just a crystal, tv modulator and some other discrete things. It's quite trivial to convert Commodore computers from one standard to another.
Yeah, but if your not handy with a soldering iron or just can't be bothered it's can be a bit difficult for some folk to tackle... :)
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OK, thanks for the info. If the motherboards are physically different (and I do believe all of you!), then why is one able to boot the NTSC machine in either mode and a PAL machine in either mode too? It must be some type of software trick fix?
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OK, thanks for the info. If the motherboards are physically different (and I do believe all of you!), then why is one able to boot the NTSC machine in either mode and a PAL machine in either mode too? It must be some type of software trick fix?
I get what you mean but the software can only temporarily switch from NTSC to PAL or vise versa, to make it permanent you'd have to modify the motherboard... :)
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Aren't there still some incompatibilities between the two, when you switch in software ?
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To make the A1200 NTSC you need to connect pin 41 of the Alice custom chip to ground, and that causes the A1200 to default to NTSC. If you are going to use the rf or composite outputs, you will need to change the built-in modulator, as NTSC signals have a different colour encoding system than PAL.
If you will only use the RGB port just do the pin ground mod and you will be set. Anyway, instead of changing the built-in modulator you can also attach an NTSC A520 external modulator.
I hope it helps. :)
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AFAIK It's determined by the Agnus/Alice custom chip version.
First agnus was ntsc only, the next two were available in pal/ntsc versions. From ECS onwards the chips are the same, the motherboard puts either 5v or ground on a pin that sets the default & you can change it in software using BEAMCON0.
It's actually misnamed as PAL/NTSC covers the colour encoding. It just changes between 50/60hz.
PAL60 is the common name for a 60hz signal using PAL colour encoding, most modern TV's support it. Some don't which is annoying if you have an xbox360 as not all games will run in 50hz.
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To make the A1200 NTSC you need to connect pin 41 of the Alice custom chip to ground, and that causes the A1200 to default to NTSC. If you are going to use the rf or composite outputs, you will need to change the built-in modulator, as NTSC signals have a different colour encoding system than PAL.
If you will only use the RGB port just do the pin ground mod and you will be set. Anyway, instead of changing the built-in modulator you can also attach an NTSC A520 external modulator.
I hope it helps. :)
Yes, quite helpful. Thanks. Any suggested ground?
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The easiest way, if you are bad at soldering, is to get ground from the back of the power connector. But the most tidy, and adequate one, is making a tiny bridge with the ground signal present in the Alice chip itself.
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To expand on what Jope mentions.. PAL/NTSC 1200 motherboards are identical.. it's just a few component differences.. To turn a PAL unit to NTSC
1. Swap X1 for a 28.6363Mhz Oscillator
2. Move R245 to R246 location (This feeds NTSC color clock from Alice/Budgie to the RGB encoder)
3. Remove R202, and place a 0 Ohm at R203 (This pulls the #NTSC pin on ALICE low, and NTSC signal on the encoder High to Select NTSC in both cases)
4. Remove the Y451 (4.336Mhz Crystal) to disable the PAL burst oscilator, since this circuit's noise seems to sometimes cause a pattern on the composite output.
Side notes (Effects the composite out only. Don't have to do this, but just to be complete):
Z221 (Band Pass Filter), would also need to be changed, but have long since gone EOL, but leaving R221 & R223 (which should also be changed) at the lower value compensates for it.
R224&R225 would also need to be modifed, if the delay line is swapped, but the delay line Z222 is also long since EOL, so you also leave this is as is, the delay is a bit off, but it's really not noticable.
After you do the changes 1-4..
The system will now boot up in NTSC, the composite output will also be NTSC, and the RF modulator output will not work (you'd need to swap it for an NTSC one)
If you only do step #3 (Similar to what Gulliver is mentioning).
This is the quickest and easiest way..
You'll have the system boot up in "sorta NTSC". The RGB will function as expected in NTSC. The composite will be monochrome only, an A520 should let you have color NTSC composite. Now, because you're in NTSC with the wrong main crystal frequency. Some Genlocks will not function, and there might be problems with serial port communications and music playback on some application that don't check the crystal speed or the graphics.library "True" flags.. This is pretty much identical to the case of choosing NTSC in the startup menu..