On 04/15/2018 05:08 PM, allison via cctalk wrote: Quite correct, Allison. I confined my answer to "Can I drop a CMOS Z80 into an NMOS Z80 socket?" And in particular, why not run the 10MHz part at the original 4MHz or whatever? A 10MHz part doesn't mean that it has to run at 10MHz. As to the rest of the question, I confess that I was blind. --Chuck

On 04/16/2018 07:23 AM, Holm Tiffe wrote: As a radio amateur and engineer in the communications realm, and embedded systems designer I know the CMOS Z80 family well.? I even have a tube of the 84C0010 (CMOS 10mhz Z80 with 1k ram and Clock Controller) which of all the 40 pin z80s is likely the ultimate part.? I designed with it a a long time ago and was an early adopter. Changing up to CMOS z80 makes sense if... you wish to reduce power, or you want to go faster, or you need a bit more operating temperature headroom. For logic levels its fully compatible save for you may not use all the capability. However in most TNCs and unless the modem side (for the RF interface)) is separately crystal controlled going faster will very likely break the unit. Why?? Ram/ROM must keep up and all the peripherals have to as well.?? An oddity of Z80 systems is that while fast Z80s were common enough the peripherals often needed added wait states for interrupt propagation and some did not have the needed speed on the bus requiring added wait states for IO.? Then we have the non z80 peripherals like the modem that may require care. The above is why the CMOS z80 with integrated clock controller was really important. Now packet modems I remember worked well even with the 2.5mhz part. Speed of the processor was rarely an issue as the RF side of the modem was generally slow as in 9600 baud max (VHF/uhf) and restricted to 1200 baud on many bands.? I helped build a digipeter (packet store and forward repeater) once and in that case CMOS was desired to allow battery backup with long up times.? A 4mhz cmos z80 (and everything else cmos) did the job well. Allison