24 May
2005
24 May
'05
6:40 a.m.
>>>> "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