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9-2 Exception Responses
If the controller receives a message which contains a corrupted character (parity check error, framing error, etc.), or
if the CRC16 check fails, the controller ignores the message. However, if the controller receives a syntactically cor-
rect message which contains an illegal value, it will send an exception response, consisting of five bytes as follows:
slave address +offset function code + exception code + CRC16 Hi +CRC16 Lo
Where the offset function code is obtained by adding the function code with 128 (ie. function 3 becomes H'83), and
the exception code is equal to the value contained in the following table:
Exemption Code Name Cause
1 Bad Function Code Function code is not supported by the controller
2 Illegal data address Register address out of range
3 Illegal data value
Data value out of range or attempt to write
a read-only or protected data
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