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Posted By

gerliczer
on 2016-09-25
09:18:15
 Re: What would I do differently in the Plus/4

Litwr, I still don't get it. What are the steps of the calculation that gives you the result of Z80 machines using the RAM at 2.5-3 MHz?

This is how I understand it works: If we have a Z80 CPU running at 4 MHz then the T-states last for 250 μs. Between two M-cycles there are at least 3 T-states, which means that the next memory access happens 750 μs after the previous at the earliest. We measure the time between the same phase of consecutive memory operations (like the start or the end or setting up CAS or anything like that), not the time passed between the end of the last and beginning of the next, because the latter wouldn't be the frequency. 1/(750 μs) ≈ 1.33 MHz.

Or did you add to that figure the RAM accesses of other devices besides the CPU?



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