11 Jul
2014
11 Jul
'14
2:37 a.m.
On Fri, Jul 11, 2014 at 3:30 AM, Kevin Keith <krfkeith at gmail.com> wrote:
I've seen 16, 22, and 24 cited as the official
number. The VAX architecture
manual seems to suggest 24. If the number is indeed more than 16, how are
they encoded? Seeing as how the manual says 4 bits are used for specifying
the specific mode, and 4 for the register selection, and seems to imply
that the operand specifier is always a byte long.
IIRC, it's like the PDP-11, which only really had eight addressing modes,
but some were considered different modes when used with the program counter
vs. a "normal" register.