Patrick writes:
> We have *one* HP 40233A cable, which works: we can connect via modem to
> the DTC and get a system prompt. But when we use the same modem and the
> same DTC port with the cables we built, the modem answers and then
> immediately disconnects.

Once again we hark back to the days before "networking" when all we had was
"datacomm", and things *never* worked right the first time you tried :-)

Back in the days when modems were the only way to connect to a 3000 from far
away, I witnessed many attempts to replicate HP modem cables in an attempt
to save money.  One of the few HP part numbers I can quote from memory is
the 30062-60022 cable which, it seemed, was the only way to make a modem
work reliably on a 3000.  Over and over people would try to use different HP
cables, or make their own based on the HP Data Communications Handbook
diagrams, or try to directly copy one of HPs cables.  For whatever reason,
these attempts were *always* failures, and we would end up falling back on
the good old 30062-60022.

Of course it's ridiculous that one should not be able to duplicate a simple
serial cable, especially given a working example to start from, but the ways
of serial communications on HP3000s have always involved a degree of black
magic and at some point it's just not worth the effort and one is forced to
give up and move on.

Buy the HP cables.  You'll live longer.

G.