Z80 instruction fetch mechanism

[Steven Hirsch]

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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