PDP 11/45 light chaser

[Gooijen H]

The drawback of the light chaser program that uses the RESET instruction
is that the heads load and unload of the RX02 drive in my PDP-11/40.
That clunck-clunck sound is not pretty for a longer while ...

- Henk, PA8PDP.


> -----Original Message-----
> From: cctalk-bounces at classiccmp.org
> [mailto:cctalk-bounces at classiccmp.org]On Behalf Of Paul Koning
> Sent: dinsdag 24 mei 2005 15:40
> To: cctalk at classiccmp.org
> Subject: Re: PDP 11/45 light chaser
> 
> 
> >>>>> "Tony" == Tony Duell <ard at p850ug1.demon.co.uk> writes:
> 
>  >> I'm not much of a Unibus expert but I seem to remember there's
>  >> something odd about what's displayed in the lights, and how you
>  >> get it to change.
> 
>  Tony> THe easiest way on an 11/45 (or an 11/70?) is to store the
>  Tony> value at the address used for the switch register (777570 IIRC)
>  Tony> and set the rotary knob to the right of the data lights
>  Tony> appropriately.
> 
> Definitely, if you have a machine with a display register (which is
> how the write-only register at 777570 is referred to).
> 
> The "data paths" setting roughly matches what you get on an 11/40,
> which doesn't have that switch.  In that case, the lights display the
> contents of R0 during a WAIT (and apparently also during a RESET).
> The fact that this happens for WAIT is the basis of the "spinning
> lights" idle code used in various operating systems (RSTS for one,
> though not RT11 which uses the display register instead).
> 
>        paul