Reference: A938
Index: B
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Instruction Manual – NPS914 Alarm and Indication IED
7.1.2. Modbus/TCP and Modbus/RTU
The device supports both Modbus/TCP and Modbus/RTU communication. Modbus/TCP uses the Ethernet
connection to communicate with Modbus/TCP clients. Modbus/RTU is a serial protocol that can be selected
for the available serial ports.
The following Modbus function types are supported:
1. Read multiple holding registers (function code 3)
2. Write single holding register (function code 6)
3. Write multiple holding registers (function code 16)
4. Read/Write multiple registers (function code 23)
The following data can be accessed using both Modbus/TCP and Modbus/RTU:
5. Device measurements
6. Device I/O
7. Commands
8. Events
9. Time
Once the configuration file has been loaded, the user can access the Modbus map of the relay via the
SMART9 software (
Tools
→ Communication → Modbusmap
). Please note that holding registers start from
1. Some masters might begin numbering holding register from 0 instead of 1; this will cause an offset of 1
between the relay and the master.
Table. 7.1.2. - 4. Modbus/TCP settings.
Parameter
Range
Description
Modbus/T
CP Enable
0: Disabled
1: Enabled
Enables and disables the Modbus/TCP on the Ethernet port.
IP port
0…65 535
Defines the IP port used by Modbus/TCP. The standard port (and the default setting) is
502.
Event read mode
0: Get oldest available
1: Continue previous
connection
2: New events only
0: Get oldest event possible (Default and current implementation) 1:
Continue with the event idx from previous connection
2: Get only new events from connection time and forward
Table. 7.1.2. - 5. Modbus/RTU settings.
Parameter
Range
Description
Slave address
1…247
Defines the Modbus/RTU slave address for the unit.
Additionally, the user can adjust the measurement update interval with the following parameters (found at
Measurement → Measurement update
). These parameters do not affect the operating times of protection
functions, only the frequency of measurement reporting to Modbus.
