23 May
2005
23 May
'05
3:21 p.m.
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.
THe easiest way on an 11/45 (or an 11/70?) is to store the value at the
address used for the switch register (777570 IIRC) and set the rotary
knob to the right of the data lights appropriately.
The first PDP11 program I ever wrote was something like
mov #0,r0 ; Initialise counter
loop: move r0.(#177570) ; Store counter in lights register
inc R0 ; increment the counter
reset ; wait a bit
jmp loop ; round again, jumos are easier to hand assemble
; than branches, but even so I got caught out
; the first time -- you use one more level of
; indirection than you might think!
-tony