Re: Z80 Softcard speed?

[Linards Ticmanis <ticmanis@gmx.de>]

Alex Freed wrote:

>> My question is, at how many MHz does the Z80 run effectively? (as long
>> as you don't switch back to the 6502, that is.
>>
>> And is this number a constant or does it depend on what instructions are
>> executed?
> 
> That's an easy one. The z80 clock pulses twice during ph1 and stays low 
> during ph0.
> So there are 2 clocks every 1 uS. This gives a 2 MHz clock. More accurately 
> 14.28/7
> or about 2.04 MHz.

Thanks!

Hmmm... what about the requirement to let the NMOS 6502 run a cycle
every 5 or so microseconds, so that it doesn't lose its register
contents? How is that handled?

And, are there no Z80 instructions that access memory on two consecutive
cycles? That would make it impossible to run these two cycles during a
single ph1, wouldn't it?

I guess I'll have to find a "what-cycle-does-what" diagram for the Z80.

And... as I said the answers are probably right before me in the
schematic, I just have to think a bit harder.

-- 
Linards Ticmanis