Re: Z80 Softcard speed?

["Alex Freed" <alexf@mirrow.com>]

"Linards Ticmanis" <ticmanis@gmx.de> wrote in message 
news:45c4da56$0$27609$9b4e6d93@newsspool2.arcor-online.net...
>
> 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?

Answered by David.

>
> 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?

Z80 has a very different architecture from 6502. Clock is faster but it 
takes
more clock to do anything.
For example an instruction fetch takes 4 clocks. Data read/write - 3 clocks
or more in some cases.

For example an instruction
    LD A, xx
will take 7 clocks and read 2 bytes from memory - opcode and a data byte.
It will also do one memory refresh cycle that will be used to refresh 6502.

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

Good idea. Plenty of free info on the 'net. I dare say Z80 was *THE* best
8 bit CPU ever. Still used to the tune of 5,000,000 a year!
Not sure if this number included derivatives like z180.

-Alex.