Mitsubishi Electric MELSERVO-JE MR-JE-C, Instruction Manual

Page: 19 / 86

2. MODBUS/TCP PROTOCOL
2 - 4
Response Message
Transaction
Identifier
Protocol
Identifier
Length Field
Unit
Identifier
Function Byte Count
Data
H L to H L
16 bits 0000h 16 bits FFh 03h 8 bits 8 bits 8 bits to 8 bits 8 bits
Message field Size Description
Transaction Identifier
(Transaction identifier) 16 bits Transaction Identifier received from the client (controller) is copied and returned.
Protocol Identifier
(Protocol identifier) 16 bits The value "0000h" is returned.
Length Field (Message length) 16 bits The byte length from Unit Identifier to Data is returned.
Unit Identifier (Unit identifier) 8 bits Unit Identifier received from the client (controller) is copied and returned.
Function (Function field) 8 bits When the message was received without errors, "03h" is returned.
Byte Count (Byte count) 16 bits The Data frame size (in units of bytes) is returned.
A value obtained by multiplying the value set for No. of Points in the Query
Message by 2 is returned.
Data (Read data) (Note 2) 16 bits × n Data starting from the start address specified in the Query Message is returned.
Data is read in order of H (higher bits) and L (lower bits).
Data is read in order starting from the start address.
Note 1. Registers can be classified into two types: registers that can be continuously accessed and particular registers that cannot be
continuously accessed.
To read particular registers, read only the target registers.
For the details on whether the target registers can be continuously accessed or not, refer to chapter 6.
2. Higher 8 bits of 1-byte data are set to "00h" when this data is returned.
To use the signed 1-byte data as 2-byte data, perform sign extension on the client (controller) side.
(2) Usage example
The following shows a setting example of when Modbus registers 2B05h (Command pulse frequency) to
2B07h (Analog torque limit voltage) are read.
Index Name Data type Read/write
No. of Points
(Number of
read points)
Continuous
read/write
Register value
(Read data)
2B05h Command pulse frequency
(Command pulse frequency)
4 bytes Read 2 12345678h
2B06h Analog speed command voltage
(Analog speed command voltage)
Analog speed limit voltage
(Analog speed limit voltage)
2 bytes Read 1
1000h
2B07h Analog torque limit voltage
(Analog torque limit voltage)
Analog torque command voltage
(Analog torque command voltage)
2 bytes Read 1 2000h