30 Oct
2010
30 Oct
'10
7:18 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?
> 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.
The one exception that pops into my head is that you cannot do a
"JMP R0" on a PDP-11. (Well, there might be a model or two where it was
allowed, since some models actually exposed the registers in the address
space, and you could execute from those addresses, but that is kindof
weird).
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.)
I am not sure wheterh the PDP11 or P800 was first,m
they both appeared in
1970 I beleive.
Would be interesting to find out more.
What do you mean by condition codes here?
The four low bits of PSW.
Johnny
--
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|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
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