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Modbus RTU interface
The COM16 module is equipped with a 3-wire RS485 interface. The Modbus RTU connector is a 9-pin female Sub-D connector with the
following pinout:
Cables connecting COM16 modules via RS485 must contain three insulated conductors and a shield. The three isolated conductors
connect to Pins 1, 5 & 9. The RS485 Reference must only be grounded at one end, preferably at the master. Grounding the RS485
Reference in multiple locations can allow common mode voltages to be imposed on the RS485 Transceiver terminals which can prevent
communication and potentially damage the device.
The cable shield must only be grounded at one end, preferably at the master. Grounding the shield in multiple locations can allow circulating
ground currents in the shield which can prevent successful communication.
Write Enable input
The COM16 Module is equipped with an input that must be activated to allow the module to accept remote control commands as well as
remote parameterization. When this input is not active, the module will reject all incoming packets that would normally change the state of
an output (open/close circuit breaker) or change protective parameters. Normal polling and communication of data are not affected.
The following commands are blocked if the Write Enable input is inactive:
- opening/closing circuit breaker
- resetting after a trip
- Changing any protective function parameters and extended protective function parameters
- changing any communications parameter (e.g. address)
- changing any parameter of the metering function (e.g. demand period length)
- resetting any diagnostic or service-related counter or indicator
- setting/resetting outputs of the digital output modules
The following commands are always allowed, independent of the state of the Write Enable input:
- changing and setting the trigger settings of the waveform capture function
- reading the contents of the waveform buffer
- changing alarm and setpoint function settings
- changing any of the customer-changeable text strings
- resetting the min/max log
- setting/resetting the "Free Output" of the COM16 module
- setting system time
Pin
1 RS485 Reference
5 Transceiver Terminal 1, V1 voltage
9 Transceiver Terminal 0, V0 voltage
2-4, 6-8 Not connected
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