HP-46 calculator (was Re: Britain is Great (Back from the Island))

From: Eric Smith <eric_at_brouhaha.com>
Date: Mon Sep 13 15:08:52 1999

Mike Ford <mikeford_at_socal.rr.com> wrote:
> I remember a combination of buttons on the 45 would make it act like the 65
> with the timers etc.

It made it act somewhat like the 55's stopwatch; the 65 didn't have one.

The stopwatch was apparently intended to be a feature of the 45 early
on in the development, but was later cancelled. The code was left in
the ROM, and was activated by STO followed by the switch under the
right half of the ENTER key. The ENTER key is molded to only press the
switch under its left half, so this feature was probably intended to be
inaccessible on unmodified calculators.

However, by the nature of a scanned key matrix, it is possible to get
a "phantom key" by pressing three other keys. In this case, it can
be done by pressing CHS, 7, and 8 simultaneously. It is difficult to
make this work consistently without a lot of work, so many people used
the "penny trick", placing a penny on those three keys to help press
them simultaneously.

Other people added a shim to the ENTER key so that it would press the
right-hand switch.

Since the stopwatch was not a supported feature of the 45, they manufactured
it using the same LC oscillator circuit of most of the other calculators,
so it isn't very accurate. Many people installed a crystal, and at some
point HP actually published an application note on doing this, although
they didn't support it, and it voided the warranty.

> Does that work in your simulator?

Yes. There's an IFDEF that makes the ENTER key generate the right-hand
keycode instead of the normal left-hand.

Eric
Received on Mon Sep 13 1999 - 15:08:52 BST