MITS 2SIO serial chip?

From: Ben Franchuk <>
Date: Wed Dec 19 21:18:41 2001

Richard Erlacher wrote:
> If you run a 20 MHz Z80 against a 20 MHz 6502, you'll find the 6502 performs WAY
> (3x-5x) faster than the Z80. It's difficult to base a comparison on clock rate
> alone. All 6502 memory cycles take 1 clock tick. Z80 memory cycles, aside from
> M1, take 3 clock ticks, with no wait states in use. If you run the 6502 at a
> rate that fully utilizes the memory bandwidth at a rate such that the Z80 can
> perform an M1 in the same amount of time, without wait states, the 6502 will
> always be faster, because it's running faster. The Z80 uses 1-1/2 clock ticks
> to execute its instruction fetch. If that's to be memory access window for each
> processor, and you run them both from static memory, and you allow minimal
> recovery time, e.g. use 10-15 ns memory, (just for the comparison) then you can
> use a 20 MHz Z80 and a 20 (actually 14) MHz 6502, and clock the 6502 with a 25ns
> low, 75ns high clock, and drive the Z80 with a square 20 MHz. That will be a 10
> MHz clock for the 6502 and a 20 MHz clock for the Z80. I'd submit that the 6502
> will still run rings around the Z80, since it is still going to be cycling
> memory at an average of 200 ns per cycle, while the 6502 does it a 100 ns rate.

What happens if you look at the M1 cycle as 2 Z80 memory cycles (2 wait
Now memory speed is the same for both but not the clock rate.
Ben Franchuk --- Pre-historic Cpu's --
Received on Wed Dec 19 2001 - 21:18:41 GMT

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