Re: How complex is the 6502?

[dempson@swell.actrix.gen.nz (David Empson)]

In article <2btddrINNa6a@iraun1.ira.uka.de> borchert@ira.uka.de writes:
> In article <2bt96o$ns0@info2.rus.uni-stuttgart.de>, zcaa1122@rpool9.rus.uni-stuttgart.de (Wulf Hofbauer) writes:
> |> >You need an instruction decoder (probably microcoded, so you could do
> |> >it with a bipolar PROM and a few support chips).
> |> 
> |> Is the 6502 microcoded? This would be a surprise to me, though I frankly
> |> don't know.
> 
> No, it's not.

Yes it is.  The "Apple Thesaurus" has an enlarged picture of the 6502's
silicon, and it describes the "large block on the left" as the
microcode ROM.  It occupies almost half the area of the CPU.

The book has a long discussion on how there is a microcode program
counter, and the microcode program has up to seven steps per
instruction (one step per clock cycle).
-- 
David Empson                                                               
dempson@swell.actrix.gen.nz                                                
Snail mail: P.O. Box 27-103, Wellington, New Zealand