On Fri, 2 Jan 2009, Jules Richardson wrote:
Someone asked this over on the Sinclair group a short
while ago, but I
suddenly thought that someone here might know...
Basically they were wondering what the internals of the Z80's instruction
fetch were, given that some instructions are multiple bytes in length, but
there's only a single-byte instruction register.
I theorised that control in the Z80 is all just a state machine, so multiple
instruction bytes presumably advance things to a new state (and what's left
in the IR during execution is just one byte from a multi-byte instruction) -
but it sounds like the OP was wondering if anyone knew the exact mechanism
(basically, has the design of the state machine ever been documented
anywhere).
Wasn't the Z80 a microcoded design?
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