Siemens UL 489 Operating Instructions Manual page 169

9.2.2.5 COM16 module
The COM16 communication module permits access to the circuit breaker via the Modbus RTU fieldbus interface.
Overview
(1) Connection terminals for additional inputs and outputs to provide special functions
(2) SUB-D plug, 9-pole, for
(3)
cLED
(4) Modbus RTU LED
(5) Connecting cables to secondary connector X8
(6) c connection for connecting external c
modules or for the terminating resistor
Installation and operation
Assembly is done as for the COM35 module:
for the guide frame → (page
for fixed-mounted breakers → (page 9-62)
Installation and operating is described in the system handbook with document order number 3ZX1012-0WL10-1AC1. 
It can be downloaded free of charge from:
http://support.automation.siemens.com/WW/view/en/39850157
Indicators
LED Indication Significance
off No 24v dc power connected
PROFIBUS
Modbus communication functioning
green
DP
red No Modbus communication or timeout
No c-modules found or 
off
no 24v dc power connected
green c communication active
c
green  cdevice found, but no 
flashing connection to ETU or metering function
red c error
Modbus RTU
connection
9-60)
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