Hopefully there are some Z8000 experts around...

A few years ago there was a post about an undocumented connection on the Z8000 CPU, which must be on the only NC/Reserved Pin on the Z8001 (pin 33). Unfortunately I can't find anything about it, although I am curious because on the Z8003 the pin is used to support virtual memory.

Historically, the convention held that 'NC' (not connected) meant there was no connection to the die -- whereas 'reserved' meant 'leave it alone' (i.e. floating) ostensibly to assure 'backward compatibility' of future versions (albeit there were a good many 'undocumented connections' bearing that designation -- the Z8000 CPU series comes to mind) --- Unfortunately the convention failed to become standard and all bets are off -- that said, I concur with @crutschow - either ground it of leave it untied but under no circumstances 'count on' the untied pin to be merely floating...

Best regards
HP

Does anybody have any idea on what it is?

Also, I recently acquired a bunch of Z8001 and Z16C01 CPUs from different vendors:


All the NMOS CPUs and the CMOS CPUs with the Zilog logo (Date code 9450, below) work perfectly. The CPUs with the Z (Date code 9834) seem to crash in a strange way, as if they disconnect from the bus without signaling it on the BUSACK line. Any idea of what this could be? Is it a bad batch, or are there some real differences?

Thanks a lot!

 

I've still got a Z80 and a few other coprocessors and ROMs. Hopefully the below might help:

 

I've still got a Z80 and a few other coprocessors and ROMs. Hopefully the below might help:

Thanks, but I am talking about the Z8000, a very different beast from the Z80…