17 Dec
2001
17 Dec
'01
7:39 a.m.
From: Richard Erlacher <edick(a)idcomm.com>
would have worked out. I think it might have given the
Z80 and edge.
Coming up
with a fair and general test might be difficult.
I'd liken 6502 VS z80 as one of those depends on what you like things.
Both have stood the test of time far better than many others.
The Z80 itself wasn't a bad CPU, but the peripheral
set they built for it,
with
its compromises in favor of the mode-2 interrupts meant
that you couldn't
use
wait-states on I/O cycles or on device chip selects to
adjust the CPU to
the
I agree, most designers did too. Look at most Z80 designs out there and it
was Z80 with NON-Zilog peripherals. Mode 2 with a little external glue to
use
with non zilog was a very potent config.
slower peripherals because it had to be looking over
the CPU's shoulder to
catch
the interrupt acknowledge and the RETI instruction.
I've recently worked
this
out by switching the clock rate during I/O and during a
pending or current
interrupt, but it's still a PAIN! What's more, it seems to require more
than
just a PAL. Handshake logic from a 4-bit wide FIFO (16
pins) seems to be
the
tool for keeping track of interrupts and their
dismissal.
:) Me, I dont use slow Zilog peripherals. The last time I used Zilog IO it
was
the 5330 SCC that ran comfortably at 10mhz with it's own DMA. A TTL
implementation of the mode 2 interrupts made for a nice system as it could
run fast, though I never bothered with RETI, as that not required and adds
much to the logic load.
Allison