Re: A86: a question


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Re: A86: a question




At 08:30 PM 4/19/98 -0500, you wrote:
>
>Could someone please explain what "T states" mean in relation to Z80
>processor speed?  I looked it up in the Z80 reference book from Zilog, but
>it didn't explain it.
>
>I've never seen "T states" or anything like that when "counting cycles" for
>the PC (which varies greatly from processor to bus to cache), so does it
>have to do with bus i/o "cycle eaters"?
>
>Please confirm this understanding:  a microprocessor's MHz is how many
>million cycles it executes per second...a 6 MHz processor like the TI-86's
>runs 6,000,000 cycles per second.  An instruction that executes in 5 cycles
>could be executed 1,200,000 times second.  But this seems a little too fast
>for the calc, but not my 50 MHz 486.
>
The MHz is actually the clock ticks or pulses per second. On some
processors, the cycles for the processor isn't the same as the MHz. For
example, the PICs' cycle is 4 clock ticks long. But in the Z80 references
T-states does mean one clock tick, so T-states is the same as the MHz. Look
at pg. 3-1 in the Z80 User's Manual. They call them T-cycles, but it's the
same thing. Chapter 3 is on timing, explains how memory reads/writes, i/o,
etc. is timed, if you're interested.

So anyway, you're right, a 5-cycle instruction should execute 1.2 million
times a second.

--Joshua


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