Omron M1 Series User Manual page 675

8-7-3
Writing to Double-word Data
The Modbus mapping function also supports double-word data. When writing to double-word data, ac-
cess the high word and the low word simultaneously. Accessing these separately will result in the
following.
• Access to only the high word: An abnormal response, returning an exception code 02 hex (invalid
address).
• Access to only the low word: Writing data to the low word only. High word data will not be changed.
8-7-4
Troubleshooting for Modbus Mapping Function
If there is any setting error for the Modbus mapping function, the inverter will display an exception re-
sponse during Modbus communication.
In this case, check the exception code for the exception response.
Below are exception codes associated with exception response and the Modbus mapping function set-
ting errors.
For details on other exception codes, refer to 8-5-9 Exception Response on page 8-20.
 Exception response for erroneous setting
The function code for an exception response is the sum of the executed function code and 80 hex.
Check the error condition with the exception code.
 Response
Slave address
Function code
Exception code
Error check (CRC-16)
Exception
code
31 hex
8-7-5 Endian Function
In communications, endian refers to the byte order in single-word communications data to be sent/
received.
Generally, big endian (where the MSB-side byte is stored first) and little endian (where the LSB-side
byte is stored first) are used.
Special endian is a kind of big endian where the word order of double-word data is reversed. For the
3G3M1 Series Inverter, Modbus communication is configured in big endian.
The endian function can set endian only for data sent/received in communications (without changing
the address).
M1 Series Standard Type User's Manual (I669)
Error condition
•
The Modbus mapping external register is
set to other than 0000 and the Modbus
mapping internal register address is not
changed from 0000.
•
The Modbus mapping internal register
setting parameter does not exist.
•
The Modbus mapping external register
overlaps.
8 Communications Functions
Countermeasure
•
Set the Modbus mapping external regis-
ter.
•
Set the Modbus mapping internal register
correctly.
•
Set the Modbus mapping external regis-
ter so that it does not overlap.
8
8-25