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
I have pair of M452 / W076 replacement boards that Vince Slyngstad offered some (
10?) years ago.
These convert the 8/L from current loop to RS232 output, and work great.
Maybe he still has some left ?
Jos