Date Code 20130214 Instruction Manual SEL-2414 Transformer Monitor
Appendix E
Instruction Manual
Modbus Communications
Overview
This appendix describes Modbus
®
RTU and Modbus TCP communications fea-
tures supported by the SEL-2414 (Transformer Monitor). Complete specifica-
tions for the Modbus protocol are available from the Modbus website at
www.modbus.org.
Modbus TCP is automatically available with the Ethernet port. Modbus TCP uses
the device IP address as the Modbus identifier and accesses the data in the Trans-
former Monitor using the same function codes and data maps as Modbus RTU.
The TCP port for Modbus TCP is 502.
Modbus Queries
Modbus RTU master devices initiate all exchanges by sending a query. The
SEL-2414 SLAVEID setting defines the device address. Set this value to a unique
number for each device on the Modbus network. For Modbus communication to
operate properly, each slave device must have a different address.
Modbus Responses
The slave device sends a response message after it performs the action the query
specifies. If the slave device cannot execute the query command for any reason, it
sends an error response. Otherwise the slave device response is formatted simi-
larly to the query and includes the slave address, function code, data (if applica-
ble), and a cyclical redundancy check value.
Supported Modbus
Function Codes
The SEL-2414 supports the Modbus function codes shown in Table E.1.
Table E.1 SEL-2414 Modbus Function Codes
Codes Modbus Description Device Description
01h Read Discrete Output Coil Status Read the status of the digital output and remote
bits.
02h Read Discrete Input Status Read the status of the digital inputs.
03h Read Holding Registers Read data from the Modbus map.
04h Read Input Register Read data from the Modbus map similarly to
function code 03.
05h
a
a
The SEL-2414 supports the Broadcast function on these functions.
Force Single Coil Control the status of the digital outputs and
remote bits.
06h
a
Preset Single Register Write data directly to a single register in the
Modbus map.
08h Diagnostic Command Test the Modbus communications channel.
10h
a
Preset Multiple Register Preset Multiple Register.
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