Drive By Pokings... Was first programs

From: Eric Smith <>
Date: Wed Jan 17 19:16:22 2001

Tony wrote:
> I've heard a rumour (and have not attempted to test it for myself, for
> obvious reasons) that using some undoucmented instructions on the HP97
> (programmable printing calculator) could fry the printhead. There was
> no way to generate these instructions from the keyboard in normal use,
> but enterprising hackers did find ways of getting them onto magnetic
> cards.

The damage would occur if you tried to print a "Non-Normalized Number"
(NNN). The microcode would get confused in a state which left the
printhead turned on. It can't handle continuous current for more than
a small fraction of a second, so it goes up in a puff of smoke.

The reason for playing with NNNs was that they allowed for interesting
displays which were useful in games.

The undocumented "instructions" of the HP-97, such as CF4, SF4, and LBLi,
*can* be generated from the keyboard using devious key sequences. But
they don't do anything.
Received on Wed Jan 17 2001 - 19:16:22 GMT

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