|50g "RS232" port|
Message #1 Posted by James M. Prange (Michigan) on 4 Aug 2006, 10:48 a.m.
From what I've read on comp.sys.hp48, the 50g's "RS232 port" is a
"serial port", but really not RS-232, so don't expect to connect
it to real RS-232 devices out of the box.
It uses a "4-pin mini-B" connector, with ground, RX, TX, and
battery voltage (+6V nominal) pins. The RX and TX pins use TTL
(3.3V) signal levels, so you'll need a level-shifter to use it
with real RS-232 devices. The battery voltage at the port seems an
obvious power source for a level-shifter, or for that matter,
anything else you want to use it for. Note that all of this seems
to be undocumented by HP so far.
HP isn't offering the required cable and level-shifter even as an
optional accessory, and at last report, has no intention of doing
so, although it might ask Samson Cables about supplying one. For
now, we're on our own when it comes to actually using this serial
port. To be sure, building a cable and level-shifter to allow the
50g to be used with RS-232 devices shouldn't be difficult, but I'd
expect HP to offer it.
Of course, the 48gII uses the same RX and TX signal levels (at its
port, not at the other end of the cable supplied with it), so
building a cable to connect a 50g to a 48gII, another 50g, or any
other device using these signal levels should be very simple.
And no, the 48gII's cable with its built-in level-shifter won't
fit the 50g. I suppose that an adapter could be made to allow
this, but note that the level-shifter in the 48gII's cable expects
to steal its power from a real RS-232 port on the other device.
For using a 48gII cable with a device that doesn't supply the
power, one could build a very simple adapter to supply power from
an external source.
Edited: 4 Aug 2006, 3:12 p.m. after one or more responses were posted