🚀 go-pugleaf

In article <405@ctycal.UUCP> ingoldsb@ctycal.COM (Terry Ingoldsby) writes:
>Does anyone know which of the CISC microprocessors are microcoded
>and which are hardwired?  I would expect the older (simpler) units
>to be hardware implementations whereas the newer (fancier?) chips
>would use microcode.  Do the vendors ever sell the same chip with
>different microcode?  I have no practical reason to know this, I'm
>just curious.

Well, it depends on what you want to call a CISC microprocessor.  The 680x0,
80x86, NS32xxx, WE32x00, NEC V series, and Transputers are all microcoded.
The newer versions of the chips, in the cases of the 680[34]0, 80486, and
32532, are still microcoded, but some of the instructions only use the ucode
to decode, and then call very specialized units (e.g., push and pop on a
'486 have hardware units on-chip that do the work, but they only get
activated after the microcode decodes the instruction).

Chips such as the SPARC, 88000, ARM, MIPS series, and the 6502 do not have
microcode; they are hardwired.  This really has nothing to do with how new
the chips are.

As to selling different versions of chips with different microcode:  yes, it
is done.  To cite two examples, the 32000 from NS was notorious for having
bugs in the chip; I think some (maybe most) were microcode bugs.  Also, the
80386 went through several revisions where there might have been slight
changes to the microcode (it looked that way).

-- 
Sean Eric Fagan  |    "Uhm, excuse me..."
seanf@sco.UUCP   |      -- James T. Kirk (William Shatner), ST V: TFF
(408) 458-1422   | Any opinions expressed are my own, not my employers'.