Explaining the Modbus Scanner - Diagnostic Objects and Exception Responses
The Modbus Scanner in Remote Connect is meant to simplify Modbus polling so that it does not have to be managed via logic. If a user finds the scanners too restrictive for their desired polling scheme, the MB_SERIAL_MASTER and MB_IP_MASTER function blocks can be used in logic and triggered as needed.
The Modbus Scanner in RemoteConnect automatically creates diagnostic objects (like Message Count and Communication Status) for each Modbus Server Device, but does NOT create objects for each individual scanner. Please note: in order to not be overwhelmed by too many objects, objects are created for only the most commonly used diagnostic parameters . A user is welcome to create objects and associate them with additional diagnostic elements.
Situations may arise where the Modbus Scanner is communicating but data is not being read or written. The Remote device could be sending an Exception Response back to the SCADAPack. An Exception Response from a remote device indicates that it understood the message (good comms) but that it is unable to perform the request (invalid function code, invalid Modbus register address, etc... ) The diagnostic objects can be used to help identify the issue and the appropriate resolution.