4 EXCEPTION CODES
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Exception code list
This section lists the exception codes that are stored in the lower byte of the response message format.
Exception code Error name Error definition and cause Action
01H Function code error The slave received an unsupported function
code.
Check the function codes that are supported by the
slave, and then check the request message sent from
the master.
02H Device address error The specified MODBUS device address is
incorrect.
Check the types and sizes of the MODBUS devices
that are supported by the slave, and then check the
address specification of the request message sent
from the master.
03H Data error The content of the protocol data unit of the
request message is abnormal.
Revise the data unit of the request message sent
from the master.
04H Processing failure Processing was not possible because of an error
that occurred during request message
processing on the slave.
Eliminate the error factor that has occurred on the
slave.
If a module is issuing this code, use the module
diagnostics or a similar method to identify the
problem from the error that is occurring, and then
perform the appropriate actions.
06H Slave busy The slave cannot execute the processing of the
request message because it is executing other
processing.
Retry at a later time.
If a module is issuing this code, revise the settings so
that the number of request messages that can be
received at the same time is 64 or less.
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