External Rs-485 Devices - Mitsubishi Electric MelcoREMOTE Installation And Operation Manual

13.5.

External RS-485 devices

Problem
READ ERROR shown on I/O
Status screen
WRITE ERROR shown on I/O
Status screen
Page 40 of 52
Possible cause(s)
External device address incorrect
Two external devices connected
on the bus with the same address
External device communication
settings incorrect
Polarity of 'A' and 'B' connections
incorrect
No ground connection
RS-485 termination / pullup /
pulldown resistors are set
incorrectly
Too many RS-485 devices
connected on the bus
External device register attempted
to be read is invalid
Value being written is out of range
Possible solution(s)
Check configured address is
correct. This setting can usually
be changed on the external
device using DIP switches or
config software.
Change the address on the
conflicting device
Check configured baud rate and
parity settings are correct. These
settings can usually be changed
in the external device using DIP
switches or config software.
Check polarity is correct.
Note: The labelling of 'A' and 'B'
can be ambiguous so try
swapping 'A' and 'B' even if this
means going against connection
diagrams
Ensure there is a ground
connection between
MelcoREMOTE and external
device
See the Connecting to external
devices section for more
information.
If there are more than 32 devices
connected on the bus then an RS-
485 repeater may be needed to
boost the bus signal. These can
be purchased from many different
electronics retailers.
Check register numbers against
external device documentation.
Check value is within range by
referring to device documentation