Zilog reintroduces enhanced Z80!

From: Allison J Parent <allisonp_at_world.std.com>
Date: Thu Sep 23 17:56:56 1999

<Just my observation, of course. Few processors would actually run that fas
<for long, but those 8 MHz parts would do it for a little while if you kept
<them cold.

I've been running them at 8 and 10 mhz for years. The cmos parts do run
cooler though even at 10mhz. To get real perfomance out of them (under CPM)
you need to have a caching bios or the disk system will definately be the
bottleneck. Also DMA is a must though the zilog DMA part never hit more
than 6mhz the 8237-5 worked just as well and didn't have to run lockstep
with the cpu.

my 10mhz machine is on s100 and the CPU is not running the bios for disk
IO thats a 4mhz z80 with DMA the the main system ram. the 4mhz cpu runs
the hard disk and caches it (it actually pushes a teltek HDCTC as it's slow
MFM) so the caching operation is invisible to the main cpu. CPM screams on
that crate. There is an 8085 configured to do the same for the floppies and
that caches at the track/cylinder level so the initial read is a bit slow
but after that it's much better as the 32k LRU cache really helps.

To date the fastest z80 system I've run (no waits) is 10mhz... I have a
z180 that clocks faster but the dram is wait state so the effective speed
is slightly less than 10mhz.

Allison
Received on Thu Sep 23 1999 - 17:56:56 BST