tops20 assembly tutorials

Rich Alderson RichA at
Tue Mar 8 13:12:16 CST 2016

From: David Griffith
Sent: Monday, March 07, 2016 11:53 PM

> Specifically I'm trying to build and run this:

>          TITLE HACK
>          SEARCH MONSYM
> HACK:   SKIPA 4,[^D4]
>          SETZB 1,3
> HACK1:  TLNE 1,777777
>           JRST HACK0
>          MOVE 2,1
>          CIRC 2,-^D18

>          END HACK

> When I do COMPILE, LOAD, and SAVE on it and run the executable, I get this:

> $hack
> ?Illegal instruction 247100,,777756 at HACK1+3
> ?Undefined operation code

As well you should.  There is no CIRC in the standard PDP-10 instruction set.
Opcode 247 is unassigned, so if someone defined CIRC locally (say, in an OPDEF,
although I don't see one here), the result you report would be precisely what
I would expect.

Where did this code come from?  From the presence of the LITES% JSYS I infer
that it has something to do with Bob Armstrong's panel.  Perhaps you should
direct a query in his direction?, and all that.


Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134

mailto:RichA at

More information about the cctech mailing list