CMOS for NMOS
allisonportable at gmail.com
Mon Apr 16 07:41:54 CDT 2018
On 04/16/2018 07:23 AM, Holm Tiffe wrote:
> allison via cctalk wrote:
>> On 04/15/2018 10:25 AM, David Griffith via cctalk wrote:
>>> I'm pondering upgrading the CPU of a Pacccomm Tiny-2 Mk2 radio packet
>>> controller from a 6Mhz Z80 processor and SIO to 10Mhz parts. My
>>> problem is that the parts already in it appear to be NMOS. The family
>>> is still being made by Zilog, but for 10Mhz parts, CMOS is all they
>>> have. Can I just drop in CMOS, change out the crystal/oscillator and
>>> have things work as expected?
>> No, and why?
>> Changing to CMOS can cut power drain. However speeding up clocks can
>> make the packet controller
>> broken even if it runs! If you keep the 6mhz clock all will be fine.
>> You do not want to alter the output data rate to the modem side. Also
>> the other devices on the bus have
>> to be able to run at 10mhz.
>> I have in the past upgraded my AmproLB+ to CMOS but that was to lower
>> power needs for
>> battery operation. However there was no intent to go faster.
>>> Here's what are fitted to my TNC.
> Power drain? ..just not interresting here. Electrically there is no problem
> changing an Z80 NMOS Part against an CMOS Version, but you are right in
> sight of the speeds of the serial connections.
> Z84C00 ..is an CMOS Variant of the CPU, Z8440 is the NMOS Version of the
> SIO ..but..
> The Z80 Processor needs external memory Parts, RAM and EPROM mostly,
> I don't think that the manufacurer of the TNC has fitted faster Parts as
> neccessary since they are much more expensive.
> Given that, you would not only get an unit that works with wrong speeds
> over serial lines, I would expect an just "not working" unit...
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
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
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
However in most TNCs and unless the modem side (for the RF interface))
is separately crystal controlled going faster will very likely break the
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
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.
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