3. Modbus/TCP
3 - 10
3.6.5 Processing at occurrence of an error
In Modbus/TCP communication, when the Query Message sent from the client (controller) includes an
incorrect value, the server (servo amplifier) returns an exception response to the client (controller).
If an error is detected in the TCP/IP layer, the server (servo amplifier) returns no message to the client
(controller).
When an exception response occurs, a value obtained by adding "80h" to the function code sent in the
Query Message is returned with an exception code.
However, no exception response occurs in the following cases.
Function code "03h" (Read Holding Registers)
When data can be read from even one of consecutive registers, no exception response occurs. In this
case, "0" is returned to the register data that cannot be read.
Function code "10h" (Preset Multiple Registers)
When data can be written into even one of consecutive registers, no exception response occurs.
Response Message
Transaction
Identifier
Protocol
Identifier
Length Field
Unit
Identifier
Function
Exception
Code
16 bits
0000h
0003h
FFh
8 bits
8 bits
Message field
Size
Description
Transaction Identifier
16 bits
Transaction Identifier received from the client (controller) is copied and returned.
Protocol Identifier
16 bits
The value "0000h" is returned.
Length Field
16 bits
The byte length from Unit Identifier to Data is returned.
Unit Identifier
8 bits
Unit Identifier received from the client (controller) is copied and returned.
Function
8 bits
A value obtained by adding "80h" to the function code of the Query Message is
returned.
When Function is "03h": "83h"
When Function is "08h": "88h"
When Function is "10h": "90h"
When an unsupported Function (example: "01h") is used, "Fu 80h"
(example: "81h") is returned.
Exception Code
8 bits
An exception code is set. For details of exception codes, refer to the following
"List of exception codes".
List of exception codes
Code
Error name
Description
01h
ILLEGAL FUNCTION
The Query Message sent from the client set a function code that the server does not
support.
02h
ILLEGAL DATA ADDRESS The Query Message sent from the client set a register address that the server does not
support. (Ex: No register address is set, or reading or writing data from/to registers is
not available.)
03h
ILLEGAL DATA VALUE
The Query Message sent from the client set data that the register cannot handle. (Ex: A
value out of the setting range is set, or "0" is set to No. of Registers.)
Summary of Contents for MR-JE-C Series
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