VOYAGER QUESTION

[Mike T.]

I'm trying to add the ability to simulate the nut processor to my simulator so I've been examining operation of the HP11C (and HP15C) microcode using the 0.78 release of Nonpariel and there is something going on that I find a bit odd.

After a cold start the calculator displays 'Pr Error' when you turn it on but the last thing it does when going back to sleep is to load the C register with zero, select the RAM bank and write -1 to register 8.

At least that is what I think the following is doing:

Code:

cycle   808  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 1-3f3  04e c=0     w
cycle   809  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 1-3f4  270 sel ram
cycle   810  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 1-3f5  260 set hex
cycle   811  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 1-3f6  26e c=c-1   w
cycle   812  P=3 q=3 carry=1  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=ffffffffffffff
 1-3f7  228 wrreg 8
cycle   813  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=ffffffffffffff
 1-3f8  1f8 rdreg 7
cycle   814  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 1-3f9  130 ldi 0521
cycle   815  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 (immediate)
cycle   816  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000151
 1-3fb  2a6 c=-c-1  x
cycle   817  P=3 q=3 carry=1  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000eae
 1-3fc  1e8 wrreg 7
cycle   818  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000eae
 1-3fd  060 powoff

When powered on again it loads the C register with zero again, selects the RAM bank as before, and reads the contents of register 8. Which now appears to be 0. Leaving me - confused...

Code:

cycle   819  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000eae
 0-000  1cf ?c  goto 00071
cycle   820  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000eae
 0-001  04e c=0     w
cycle   821  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 0-002  270 sel ram
cycle   822  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 0-003  238 rdreg 8
cycle   823  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000        ** ??? - What happened ?
 0-004  2ee ? c<>0  w
cycle   824  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 0-005  0ff ?c  goto 00044
cycle   825  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 0-006  371 ?nc call 01734
cycle   826  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 (long branch)
cycle   827  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 0-3dc  260 set hex
cycle   828  P=3 q=3 carry=0  stat=...........b..
 a=00000000000000 b=ffdafeaacaffff c=00000000000000
 0-3dd  0a0 sel p

Any clarification would be very welcome!

Thanks