PDP-11/05 returns to life

[Johnny Billquist]

Paul Koning <Paul_Koning at Dell.com> wrote:

 >>>>>> >>>>> "Henk" == Henk Gooijen <henk.gooijen at hotmail.com> writes:

 > >> 2. Is there a chasing lights program I can run on the 11/05? Would
 > >> be nice to see it visibly doing something
 >
 > Henk> Search the net. There is a small program (estimate 7 words). It
 > Henk> uses the RESET instruction (is that 000005?) ... not nice if
 > Henk> you connect an RX01 or RX02 to the machine as on every RESET
 > Henk> (INIT) the heads clunk!
 >
 > That's a bit ugly...

Definitely.

 > A cleaner one is the RSTS null job.  It relies on the fact that a
 > number of PDP-11s -- including the 11/05 as far as I remember -- will
 > display R0 in the lights during a WAIT instruction.
 >
 > RT11 won't do, that uses the status register so you need a machine
 > that has it and that displays it.  I forgot what RSX does.  Not sure
 > you could run that on an -05 anyway.

RSX uses the side effect of R0 being shown on the data bus on a WAIT 
instruction as well.
And yes, I think you could get RSX running on an 11/05. I don't think 
there was any PDP11 that couldn't run RSX, but it would be a rather 
specific RSX you would gen for it. I doubt you could boot any generic 
RSX system on that machine. Instead you would have to run the sysgen on 
another machine, and just boot the resulting system on the 11/05.

Think unmapped RSX. That won't use any MMU. Still, you'd probably want 
the full 56K on that machine.

 > Sufficiently old RT11s should work on that machine.  So would RSTS
 > V4A, if you can find an RK05 or RF11 or RP03 disk drive.   :-)

New versions of RT-11 should do as well, as long as you select a variant 
that don't need the MMU. Same goes for RSX, except that RSX won't be 
self-hosting.

 > RSTS null job looks like this:
 >
 > ; THE SIMPLE NULL JOB
 >
 > 10$:	MOV	R2,R1		;RELOAD THE WAIT COUNTER
 > 20$:	WAIT			;DISPLAY THE LIGHTS (R0) A WHILE
 >	SOB	R1,20$		;KEEP WAITING
 >	ROL	R0		;ELSE SHIFT PATTERN 1 PLACE LEFT
 >	BR	10$		; AND AROUND AGAIN...
 >
 > You need a periodic interrupt, of course, to break out of the WAIT.

And RSX is something similar. Fool around a little, set up R0, and WAIT. 
The clock interrupt would break you out.

	Johnny