HP TSB console lockout (was RE: HP (3rd party) id help?

Jay West jwest at classiccmp.org
Fri May 1 09:04:56 CDT 2015

Rick wrote...
 The computer center (as it was called then) was very much off limits to
just about anyone but the operator, ...
Maybe it is/was common knowledge, but I had forgotten about this tidbit
until finding a 1 sentence note almost hidden in a manual...

To keep people from entering commands at the console who were not
authorized, TSB monitors bit 0 of the S register on the main cpu. If that
bit is set, no console commands will run and it just echos back the
characters that you type. On the older machines where the front panel key
switch actually could lock the panel, for security if people had access to
the machine room you could set Sreg bit 0 and turn the key to lock and take
it with you. Console disabled.

I was curious if this would work with the newer cpu's where the key switch
was just a door latch and the "lock/operate" switch was behind the front
panel. Alas, sr0 bit 0 works as expected to lock the console, but setting
the lock/operate switch behind the front panel does not disable the switch
register. So on those model cpus... I guess it's "security through
obscurity" :)


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