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Is a 6502 processor always a 6502 processor?

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Hi all,


I have a question regarding the "general" learning/programming of the 6502 processor.


I am currently learning ASM programming for the Atari 2600 and as I am studying, I am learning the specifics of the 6502 processor registers, etc. (nothing new here)


Once I have a general understanding of the 6502 ASM "in's and out's", will it then be "somewhat" (certainly different in many ways) manageable to then move to programming other 6502 based machines?


I would like to branch out to some of my childhood favorites (Commodore PET and VIC-20) as well in the future.

What are your thoughts please?


(apologies if this is an improper place for this post)




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for the most part, yes.   The instruction set and registers will be the same.    What you will need to relearn is how each system handles, text, graphics, sound, etc.


Some systems use variations like the 6510 which might have small differences.   I don't recall what they were.

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The MOS 6502, 6507, 6510, and 8502 have identical instruction sets (and registers).


The 6507 has the reduced address bus;

The 6502 is the baseline model (‘lawsuit-compatible’ version of the 6500)

The 6510 has a parallel port addressed at locations 0 & 1, used on the Commodore 64 for memory banking controls and Datasette interface

The 8502 is a 6510 with glue for the Commodore 128's FAST mode and co-operation with the Z80 coprocessor.


The WD 65C02 (used in some Apples, among other things) adds a few instructions and does away with most of the undocumented (‘illegal’) instructions (like, say, ‘lax’)


The WD 65816 adds a 16-bit mode but maintains the full 8-bit instruction set, again at the cost of losing the undocumented instructions.


The Ricoh RP 2A03 and 2A07 from the NES are instruction-set compatible (including undocumented instructions) with the 6502 for the most part, but Decimal mode is not available, and the sound generator (APU) is on the same chip.



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3 hours ago, Keatah said:

What about 6502C "Sally"?

The 6502C Sally used in the Atari 8-bits has an additional HALT signal (active LOW) on pin 35, which facilitates waiting for the next scanline by strobing WSYNC, just as on the VCS. Moreover, there's a duplicate R/W signal on pin 36. (Both pins, 35 and 36, are not connected on the stock 6502 and reserved for "future expansions".)



Edited by NoLand
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On 4/23/2020 at 6:09 PM, JohnnyRockets said:

What are your thoughts please?

Think of it like learning a language. British English is slightly different from American English, but they understand each other. So is CMOS 6502 compared to NMOS 6502. I suggest reading the Wikipedia articles for the different versions of the CPU to get an impression.

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