pdp-11 assembly standards

Paul Koning paulkoning at comcast.net
Tue Jan 10 11:02:21 CST 2017

> On Jan 10, 2017, at 8:03 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
>> From: Brent Hilpert
>>>>> One assembler doc uses a prefix of "&o"
>> So the answer is, by modern expectations the old standard would be
>> ambiguous or misleading.
> Well, the ideas of 'assembler' and 'standard' don't really go together in my
> mind... :-)
> But seriously, I don't know how many different PDP-11 assemblers there were,
> but the two _main_ ones (DEC's, and Unix's) both use the same numeric
> convention (although they differed in other ways, probably because of the
> CTSS/Multics erase character convention): a sequence of digits is an octal
> number, unless there's a trailing '.', in which case it's decimal.

Is that the Unix assembler convention?  It certainly isn't the one used by the GNU assemblers, which are modeled after the old Unix syntax.  That one assumes decimal, and doesn't appreciate decimal points after a digit string.  

I wonder why DEC changed comment markers in their assemblers (from / in the PDP-8 to ; in the PDP-11).  Yes, not using / frees it for use in expressions, but at least early on it wasn't supported there.


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