Z80 CPU compatibility

[Tezz]

Are there any Z80 CPUs that are not compatible with the ZX81? I'm looking at buying a few but I'm not sure regarding compatibility. There are several available to buy on ebay for example such as an original Zilog Z80 (Z84C0006PEC), SGS Electronics Z8400PS and newer CMOS type Zilog CPUs (Z84C0020PEC) with higher clock speeds.

thanks.

[1024MAK]

All rated at 4MHz or greater should work. Sinclair used various types. The most common are Zilog and NEC, but you will also find others like SGS. Of course, all these are NMOS types. And the official licensed versions should work the same as the Zilog versions. Browse through the various threads with PCB pictures to see the different CPUs that are in use. E.g. this thread

There are however some (as far as we know, a very limited number) of machines where they are fussy over which CPU will work correctly when certain expansions are used.

Zilog still make new Z80 CPUs, but they are now CMOS technology parts. But these work just as well. See here.

Mark

[Tezz]

Thanks again Mark, much appreciated.

[RetroTechie]

Just get a CMOS version (Z84C00xx), it'll run cooler. I've even had East-German Z80 clones (UB880 = 2.5 MHz version) working in a ZX81. Which isn't surprising since a 2.5 -> 3.25 MHz overclock is quite moderate by Z80 standards.

Working fine in ZX81 but problems with peripherals attached = problem caused by peripheral (imho).

[Tezz]

Thanks, I've done just that today and bought a few Z84C00xx CPUs