17 Jan
2001
17 Jan
'01
7:16 p.m.
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.