1 Mar
2006
1 Mar
'06
8:26 p.m.
On 3/1/2006 at 3:07 PM John C. Ellingboe wrote:
While this is normally reliable, be warned it doesn't _always_ work. The
HP48 calculator has the signal ground pin of the (minimal) serial port
connected to the +ve supply line. There's an internal voltage converter
which doubles the logic supply, the transmit data pin swings between
this doubled supply voltage an logic ground, so about -5V to +5V wrt the
logic +ve line which is the RS232 signal ground.
Does anyone have information on the TI Travelmate
LT220/V. A
quick Google didn't turn up anything of value.
I have acquired one with a pile of other items and have no idea
how useful it might be. The power source, 18V DC did not come
with it and there is no indication as to whether the center pin
of the power connector is the positive connection or not.
Any external I/O connectors on it? Things like parallel port connections
will usually have their ground/return pins conected to the - side of the
power supply.
Last resort is popping the box open and checking the ground plane on the
PCB or any of the ICs (if the ground plane is buried) against the
connector.
That's the one I do first. Why 'as a last resort'?
-tony