Mitsubishi Electric MELSERVO-JE MR-JE-C Instruction Manual page 19

2. MODBUS/TCP PROTOCOL
Response Message
Transaction Protocol
Length Field
Identifier Identifier
16 bits 0000h
Message field
Transaction Identifier
(Transaction identifier)
Protocol Identifier
(Protocol identifier)
Length Field (Message length)
Unit Identifier (Unit identifier)
Function (Function field)
Byte Count (Byte count)
Data (Read data) (Note 2)
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
2B05h Command pulse frequency
(Command pulse frequency)
2B06h Analog speed command voltage
(Analog speed command voltage)
Analog speed limit voltage
(Analog speed limit voltage)
2B07h Analog torque limit voltage
(Analog torque limit voltage)
Analog torque command voltage
(Analog torque command voltage)
Unit
Function
Identifier
16 bits FFh 03h
Size
16 bits Transaction Identifier received from the client (controller) is copied and returned.
16 bits The value "0000h" is returned.
16 bits The byte length from Unit Identifier to Data is returned.
8 bits Unit Identifier received from the client (controller) is copied and returned.
8 bits When the message was received without errors, "03h" is returned.
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.
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.
Data type
4 bytes
2 bytes
2 bytes
Byte Count
H
8 bits 8 bits 8 bits
Description
No. of Points
Read/write (Number of
read points)
Read 2
Read 1
Read 1
2 - 4
Data
L to H
to 8 bits
Continuous Register value
read/write (Read data)
12345678h
L
8 bits
1000h
2000h