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11
RS232/RS-485 Communications Converter - QD1010b
• Once a network is wired, you should test communi-
cations with all controllers on the network. Find out
which controllers communicate and which ones don't.
Go to the controllers that don't communicate and ver-
ify that the "A" and "B" wires are not switched. Verify
the address and the baud rate as well. One of these
three things is usually the problem. (see chart below)
IF
THEN
Check that the baud rate set on the controller(s) are
all set the same. Verify controller address.
Rx LED is always on. This is typically a problem with wir-
ing.
Check wiring. Make sure that communication wir-
ing runs are at least 5' away from fluorescent lights,
motors, etc. Make sure that all controllers on a net-
work have a unique address.
Make sure that the "A" and "B" wires are not switched
or shorted. Make sure that there is no stray voltage
on the "A" and "B" wires. "B" to "A" should measure
between 0.5 VDC and 3.6 VDC. "B" to "A" should
measure 0 VAC. "A" to "Shield" and "B" to "Shield"
should measure 0 VAC and 0 VDC.
Both Tx and Rx LEDs will blink. Both the computer and the
controller are responding, but you still receive communica-
tion errors.
Tx LED blinks, Rx LED is always off. If this happens, the
computer is sending, but the controller is not responding.
On smaller networks, try removing one of the two ter-
minating resistors.
Communication errors/problems.
Rev:1116
C3786_REV1
