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9 EXCEPTION RESPONSES
The exception response codes sent by the slave are shown in Table 9.1. When a slave detects one of these errors, it sends a
response message to the master consisting of slave address, function code, error code and error check fields.
Exception
Response
Exception Response Name
Code
01
Illegal Function
02
Illegal Data Address
03
Illegal Data Value
07
Negative Acknowledgement
08
Memory Parity Error
9.1 Examples
A read register request to read holding register address 251 of slave 01 (undefined address for slave, beyond address limit) is
shown below.
Register Start
Slave
Function
Address
01
03
The response is an exception response sighting 'illegal data address'. To indicate that the response is a notification of an error,
the most significant bit of the function code is set to 1.
Slave Address
01
12
The message function received is not an allowable action for the 8240.
The address reference in the data field is not an allowable address for the 8240.
The value referenced in the data field is not allowable in the addressed slave location.
The function just requested cannot be performed.
Parity check indicates an error in one or more of the characters received.
Table 9.1 Exception Response Data
Register Start
Offset High
Offset Low
00
FA
Function
Exception Code
83
Exception Response Definition
Number of
Number of
Registers High
Registers Low
00
06
02
Error Check Field (CRC-16)
E5
Error Check Field (CRC-16)
CO
F1
F9
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