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Re: /etc/disktab on vax
On 07/03/2012 02:54 PM, Mouse wrote:
>>> IIRC the Z80 required a 4x clock, so a 20MHz Z80 is about as fast as
>>> a 5MHz 8080 or 8085.
>> It's not that the Z80 "requires a 4x clock", but four T-states (clock
>> cycles) make up one machine cycle. [...]
> Also - and this memory is seriously fuzzy, so it could be entirely
> wrong - I think the 8080 required a two-phase clock, so that there are
> four, not two, state changes on the clock pins per clock cycle. This
> could easily turn into "requires a 4x clock", so if my memory is right
> and the Z80 copied that particular bit of design....
The 8080 does require a two-phase clock, but they're at the same
frequency, and nonoverlapping, so they're (sorta) easy to generate. The
8224 generates them from a single crystal.
You make a good point, but the Z80's clocking subsystem bears no
resemblance to that of the 8080.
Dave McGuire, AK4HZ
New Kensington, PA
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