IAI America ROBO Cylinder Series - Manual (Page 310)

7. T
roubleshooting
302
Modbus
7.1 Responses at Errors (Exception Responses)
In each query (command), except for a broadcast query message, the master issues a query by expecting
a “successful” response(response), and the applicable slave must return a response to the query. If the
query is processed successfully, the slave returns a “successful” response. If an error occurs, however,
the slave returns an exception response.
The slave responds to a query in one of the following four ways:
(1) The slave receives the query successfully, processes it successfully, and then returns a “successful”
response.
(2) The slave returns no response because the query could not be received due to a communication error,
etc. The master generates a timeout error.
(3) The slave also returns no response if the query is received but is found invalid because a LRC/CRC
error is detected. In this case, the master also generates a timeout error.
(4) If the query is received properly without generating errors but it cannot be processed for some reason
(such as when the applicable register does not exist), the slave returns an exception response that
contains an exception code indicating the content of exception.