Can Atari PIA be replaced by M6821P ?

[manterola]

Title really said it all. M6821 is widely available. I plan to use it on an Atari 600XL

Thanks

[Rybags]

Pinouts the same, registers seem to be the same. Plenty of Ataris use 6820 and I found a pinball page which suggests using 6821 as replacement for 6820.

So, worth a shot.

 

Another page I found says

 

Supposedly all PIAs are program/pinout identical, but their electrical characteristics vary slightly. The original 6820 is unique because it's fabricated using the "enhancement mode" NMOS process whilst the later 6821 and the MOS 6520 are depletion mode. (Motorola started moving the whole 6800 product line over to depletion mode in 1976.) So if you want the thing to be *exactly* correct for an Apple I you have to find a 6820.

That said, depletion mode NMOS is both faster and more electrically stable. So there's a non-zero chance that swapping your 6820 for a 6520 or 6821 will actually improve its reliability.

 

http://www.applefritter.com/?q=content/questions-about-pia

Edited February 20, 2018 by Rybags

[Simius]

M6821P is functional and pin compatible with Atari PIA (MOS6520) but it is 1MHz version. Atari requires 2MHz version: M68B21P

[Marius]

Simius is right. I even have Atari XE pcb's with M68B21P.