OT-DIY CPU's

From: Andy Holt <andyh_at_andyh-rayleigh.freeserve.co.uk>
Date: Sun Aug 18 15:18:01 2002

> Of course if you have a 12 bit or 24 bit word, then either octal or hex
> are natural (3 hex digits = 4 octal digits). Again I guess which one you
> use depends on the format of the instruction word.
>
The fun then comes with something like the ICT/ICL 1900 series* where the
24-bit word and the 7-bit opcode were "always" expressed in octal but the
instruction
F X N(M) was physically laid out as
X(3 bits)F(7 bits)M(2 bits)N(12 bits) [branches being slightly different]
which did not appear naturally in the octal expression.

* originally the FP6000 originating in Canada

Andy
Received on Sun Aug 18 2002 - 15:18:01 BST