tops20 assembly tutorials

David Griffith dave at
Wed Mar 9 18:14:02 CST 2016

On Tue, 8 Mar 2016, Rich Alderson wrote:

> 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.

I got it from Jan deRie when I asked about it on a Youtube video[1] 
showing the Panda Display in action.  I'm trying to get it compiled 
because I've made a new Panda Display board[2] that connects to a USB port 
instead of a parallel port.  The new board works, but the lights don't 
light up as expected, so I need something that puts a recognizable pattern 
on the display.

I'm doing this with Bob Armstrong's blessing, but I haven't asked him 
about this program yet.  I'll post to the Spare Times Gizmos list now.


David Griffith
dave at

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