PAL vs NTSC CPU differences

[e1will]

I've read that the clock speeds of the PAL 6507 and NTSC 6507 are about 1% different... is that the only difference? Are the CPU functions identical other than that?

 

Specifically I'm wondering if any of the illegal opcodes that encounter race conditions when executing produce different results on the different console types. (Probably not since the CPU would just be racing against itself...)

 

And yeah, this is sort of a back-door way of re-opening the question whether it would be possible to write code to test whether a PAL or NTSC console is running. From what I've read in the archives there doesn't seem to be much hope, but you never know...

 

(And at any rate, if there was a way to programmatically check this, you'd probably still want an option to override the default TV type in case the code guessed wrong. I like the way "Man Goes Down" handles it: the Select switch changes the type, and the game then "remembers" the preferred setting via the AtariVox if one is present.)

 

--Will

[Thomas Jentzsch]

Chances are IMO much better when looking for TIA differences. Though even there noone has found anything yet.

[+batari]

I've read that the clock speeds of the PAL 6507 and NTSC 6507 are about 1% different... is that the only difference? Are the CPU functions identical other than that?

 

Specifically I'm wondering if any of the illegal opcodes that encounter race conditions when executing produce different results on the different console types. (Probably not since the CPU would just be racing against itself...)

 

And yeah, this is sort of a back-door way of re-opening the question whether it would be possible to write code to test whether a PAL or NTSC console is running. From what I've read in the archives there doesn't seem to be much hope, but you never know...

 

(And at any rate, if there was a way to programmatically check this, you'd probably still want an option to override the default TV type in case the code guessed wrong. I like the way "Man Goes Down" handles it: the Select switch changes the type, and the game then "remembers" the preferred setting via the AtariVox if one is present.)

 

--Will

There is a glitch in the playfield in score mode when the players are different colors and the playfield covers the center portion of the screen. Sometimes you get a vertical thin line of garbage where the colors meet. Perhaps that is not there on a PAL TIA, and/or maybe the garbage also affects something you can read (such as collision registers?)

 

Anyway, Melody/Harmony should be able to detect what console it's running on, provided the 2600's clock itself is accurate enough.

[SeaGtGruff]

I've read that the clock speeds of the PAL 6507 and NTSC 6507 are about 1% different... is that the only difference? Are the CPU functions identical other than that?

Maybe I'm mistaken, but isn't the 6507 just the 6507-- there's no "NTSC" version or "PAL" version of it? The 6507 doesn't generate the clock pulses, does it? I thought the clock pulses have to be generated by an onboard crystal oscillator, and are then fed into the TIA, which divides them by 3 to get the machine clock cycles, which are then fed into the 6507? The 6507-- and, for that matter, the 6532-- doesn't have "NTSC" or "PAL" or "SECAM" versions, does it? It's just the TIA that comes in different "flavors" like that? (I mean, sure, there are/were different versions of the 6507 chip based on its maximum operating frequency-- 1MHz, 2MHz, 3MHz, or 4MHz-- but that has nothing to do with "NTSC" versus "PAL" frequencies.)

 

Michael

 

Edit: So I guess my quick answers are, "The clock speed isn't determined by the CPU," and "The *CPU* functions are the same on an NTSC 2600 and a PAL 2600, because they have the same CPU."

Edited July 22, 2009 by SeaGtGruff