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>In article <32...@news.Think.COM> r...@think.com (Robert Krawitz) writes:

>I had the good fortune to acquire an HP-45 calculator free of charge
 Connoiseurs of the '45 are aware of the
>undocumented stopwatch feature (resolution to .01 second, 10 "splits",
>and time/decimal conversion, but the clock frequency was wrong; it was
>something like 14% slow, but I forget the exact conversion constant).

OK, the real story.
The processor inside an original HP is really weird. 56 bit serial data, 10
bit instructions. ROMs were 256 word serial- address was serial in, data was
serial out. The HP35 had 3 ROMs. The -45 was to have 7. The HP80, which came
out second, had 5?6? ROMs. There was enough room in on of them that the
programer (France' Rode') put in the stopwatch feature. However, in order to
get room to fix a bug, it was removed (The HP35 had exactly one word space,
and it was in a place that was completely inaccesible, ever!)

Just before the HP45 was released, Mostek came to HP and said they had come
up with a quad ROM; 4 times as dense. Was HP interested? Yup. All of a sudden,
there was one whole equivalent ROM left. The day the ROMs were released, the
programmer (Peter Dickenson) stuck the stopwatch code in, whole.

Timing was based on a LC oscillator. To get consistent, accurate timing, it
had to be replaced with a 784kHz crystal (which the HP55 used).

>Another interesting thing that sometimes happened was that I'd get a
>wholly incomprehensible display, with a variety of numbbers separated by
>blanks on the display.  When I hit a certain key, a new set of numbers
>would be displayed.  I never did learn what that was about, but I always
>suspected that it was some sort of microcode debugger/stepper left in

There was never enough room for a debugger. What you saw was the display
format register being screwed up.

Originally, stopwatch mode was supposed to be inaccessible to anyone who hadn't
re-wired their machine. The 'Enter' key was double wide; there were actually
two keys, but only one was connected. If you connected the other, it would
go into stopwatch mode when the right key sequence was used. However, because
of the key scanning, that key could be made to look like it was depressed when
the three keys above and/or to the right were simultaneously depressed. That
is how the whole story leaked out. This trick was not considered by the 
programmer.

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