22 Jul
2005
22 Jul
'05
9:22 p.m.
Assuming that things obey the standard, which pre-PC
stuff usually
did, you can tell from the connector gender whether you need a null
modem or not. If the connector is DB-25 male, use a null modem cable;
if female, use a straight through (DTE to DCE) cable. The former is
what I would expect, but surprises happen...
I find one of those little in-line RS232 testers very useful for this.
Just plug the appropriate end into the connector and see whether it
drives pin 2 or pin 3. You can also see what, if any, handshake lines it
drives.
And if you get a crazy pattern of lights, it's a good bet it wasn't an
RS232 device in the first place.
-tony