Processing At Occurrence Of An Error - Mitsubishi Electric MR-JE-_A Instruction Manual

3. MODBUS PROTOCOL

3.4.5 Processing at occurrence of an error

In the Modbus-RTU communication, when the Query Message sent from the master (controller) includes an
incorrect value, the slave (servo amplifier) returns an exception response to the master (controller).
When a parity error, CRC error, overrun error, or framing error occurs, the slave (servo amplifier) does not
return a message to the master (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.
When the function code "03h" (Read Holding Registers) is used
When data can be read from even one of continuous registers, no exception response occurs. In this
case, "0" is returned to the register data that cannot be read.
When the function code "10h" (Preset Multiple Registers) is used
When data can be written into even one of continuous registers, no exception response occurs.
The following shows the Response Message to be sent at occurrence of an exception response.
Response Message
Slave Address Function
(8 bits) (8 bits)
Message
Slave Address
Function
Exception Code
CRC Check
List of exception codes
Code Error name
01h ILLEGAL FUNCTION
02h ILLEGAL DATA ADDRESS
03h ILLEGAL DATA VALUE
When an exception code is generated, a CRC error may occur at the same time.
CRC Check
Exception
Code
L
(8 bits) (8 bits)
Size
8 bits The station number of a slave (servo amplifier) is returned.
A value obtained by adding "80h" to the function code of the Query Message is
returned.
When Function is "03h": "83h"
8 bits When Function is "08h": "88h"
When Function is "10h": "90h"
When an unsupported Function (example: "01h") is used, "Function + 80h"
(example: "81h") is returned.
An exception code is set. For details of exception codes, refer to the following
8 bits
"List of exception codes".
Data for CRC error check
16 bits
This data is calculated automatically by a servo amplifier, and the result of the
calculation is returned.
The Query Message sent from the master set a function code that the slave does
not support.
The Query Message sent from the master set a register address that the slave
does not support.
(Ex: No register address is set, or reading or writing data from/to registers is not
available.)
The Query Message sent from the master 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.)
3 - 10
H
(8 bits)
Description
Description