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Finding replacement 6502 for AppleII+


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Was just gifted an AppleII+, unfortunately it's missing the CPU for unknown reasons. I'm hoping it's not trash and I'm willing to put in a few bucks to experiment. 

 

 

Is there any guide on picking a 6502 replacement for an AppleII+? I picked up a pair of R65C02P4 processors from eBay because they were particularly cheap but I neglected to check whether they'd be suitable drop-ins. Mouser has the WDC W65C02S6TPG-14 for $10 a pop but shipping to Canada was $20 so I opted not to go with that. Not sure I made a good choice.

 

Can I expect my R65C02P4 to work fairly well, or should I be planning on another purchase?

 

Thanks!

 

 
 

 

 

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.. as for the 65C02s you bought... you might have problems. They're (mostly) elecrically compatible but there is some software for the II and II+ that depends on "undocumented instructions" that were replaced with NOPs on the CMOS versions. (This same software breaks on Apple IIcs and IIes for that reason.)

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I did some digging and it sounds like you should be fine from a "it won't damage anything" standpoint, but it might not work. Apparently some people have tried swapping in 65C02s intentionally to get some C-dependent software running on Plus's and they've run into issues they think are memory timing related. (Here's a thread. Apparently some work, some don't, and it may depend on the exact mix of ICs in your particular II. No offense to the almighty Woz but Apple II is frankly a pretty skanky design when it comes to sticking to specs.)

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Yes. It was typical back in the day for CPU manufacturers to add letter suffixes to their chips to indicate higher speed versions. In the 6502's case the standard no-letter version is 1mhz, a 6502A is rated for 2Mhz, and a 6502B is good for three.

(If you're looking at Z-80s the no-letter, A, and B ratings correspond with 2.5mhz, 4mhz, and 6mhz respectively, so the letters themselves don't mean anything specific. Oddly enough the next step up with Z-80s is the Z-80H, while some second-sources made 4mhz 6502s with a C suffix... not to be confused with a C in the middle, which means CMOS process and additional instructions.)

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