31 Oct
2010
31 Oct
'10
11:12 a.m.
On 2010-10-30 01:12, ard at p850ug1.demon.co.uk (Tony Duell) wrote:
Could you use it like any other register?
There were some restrictions. I don't think you could shift it (at least
ont on the P850). But for many instructions it was just another register.
> I have not seen anyone comment any of the
other things I listed as
> possible firsts on the PDP-11.
> Can anyone come up with an earlier machine that used condition codes?
> How about general registers with addressing modes, which is totally
> orthogonal? How about having the PC as a general register?
The Philips P800
series has the PC as a general register (register 0). There are 16 registers, some instructions can
only use the first 8, others
can use all 16. Addressing modes (simpler than the PDP11, I admit) are
pretty much orthogonal.
Sounds like the registers were atleast not as orthogonally used as on a
PDP-11. If an instruction could take a register, it could take any
register. And all addressing modes are valid (well, almost) anywhere. One wonderful thing about the PDP-11, which
unfortunately did not get
copied, was the nice things that happened because the PC was e general
register. Thus, the PDP-11 never had special versions of instructions to
implement immediate mode operands, and so on. All that was solved
because the PC was a general register.
(Well, the VAX sortof have it, but no other machine I know of.)
As I just mentioned, the P800 family did it this way too.
What do you
mean by condition codes here?
The four low bits of PSW.