Path: utzoo!attcan!uunet!ncrlnk!ncrcae!ncr-sd!hp-sdd!hplabs!hp-pcd!hpcvca!daver
From: daver@hpcvca.HP.COM (David Rabinowitz)
Newsgroups: comp.sys.hp
Subject: Re: HP 9825A (was Was *this* the first RISC chip?)
Message-ID: <4480011@hpcvca.HP.COM>
Date: 10 Mar 89 17:39:27 GMT
References: <16274@mimsy.UUCP>
Organization: Hewlett-Packard Co., Corvallis, Oregon
Lines: 24

>On the Nut series of CPUs (HP-41, HP-1x), and I presume on the earlier
>versions, not all instruction are one word in length.  Load immediate (LDI),
>power off (POWOFF) and absolute branch (CGO & NCGO) and calls (CXQ & NCXQ)
>are all two word instructions taking two cycles and the ROM fetch instruction
>(RDROM) is a one word instruction that takes two cycles.

The original processor had only single word instructions which were referred to
as "states" (the machine was designed by EEs who thought in terms of state
machines, so in a way it really was a RISC machine).  It was tightly optimized
for the HP-35, and as a result the entire calculator was implemented in only
768 states.  By the time the 41C CPU (originally named Nutmeg) was designed,
several generations later, the instruction set had been enhanced to include
multi-state instructions.  There is no write-to-ROM instruction, but a
read-from-ROM-at-a-computed-address instruction was added to allow use of ROM
tables and efficient storage and access of user code in ROM.  The original
processor had a 1-state load immediate instruction which loaded a single digit,
and all jumps were one state (7-bit address offset).  The 41C and CV
calculators have 12K states and the 41CX has 24K states of code in the
mainframe.

By the way, I believe the first 1-chip 16-bit microprocessor in production was
the MC^2 chip which was released in 1976.  The part was CMOS in an SOS (silicon
on sapphire) process.  It is described in Osborne's volume 2 though none were 
ever sold except inside HP products.