Hi all --
I'm attempting to get my 8/L talking to the outside world. It's
outfitted with the typical Teletype interface, which I'm attempting to
connect to a PC via acurrent loop to RS232 adapter.
Specifically, I've got one of these:
http://www.bb-elec.com/Products/Serial-Connectivity/Serial-Converters/Curre….
At the moment I have it configured (per the manual) assuming the 8/L is
an active loop device (i.e. the converter's transmit lines connect to
the 8/L's receive lines, and the 8/L's transmit lines connect to the
converter's receive lines). With this configuration I'm able to get the
8/L to send data to the PC successfully.
I'm not having much luck getting the8/L to receive anything from the PC,
however. If I put my multimeter in the loop, I see a current of about
40mA, which drops to between 30 and 37mA when the PC is sending data
(depending on what data's being sent). However, I'm not getting much of
anything onpin "E" of the W076 (Teletype Connector) board -- this is
supposed to be the "Logic Output" and I'm assuming that should be the
TTL-level data signal, correct?
I do see a very, very tiny signal (in the millivoltrange) on pin "E"
that matches up with the data being sent from the PC, but it's obviously
nowhere near the correct level. I've gone over the W076 board and
checked the related diodes and resistors for anything open/shorted. And
I actually did find a bad diode (fell apart when I desoldered one leg to
test) but replacing it made no apparent difference.
At this point I'm wondering if the loop configuration I have is
incorrect. I thought this was supposed to be a 20mA loop, but I'm
getting 40mA. I know very little about the fundamentals of current loop
stuff, so I could be way off here.
Anyone have any advice?
Thanks,
Josh