The Mercedes W2xx plugin for the KWP2000 component implements some special functions needed for communication with the W2xx ECU series over CAN busses.
The Mercedes W2xx plugin implements the start diagnostic session (DBDiagnosticMode $92 used for starting communication and Default/OBDMode $81 used for stopping communication) request as well as an asynchronous TesterPresent message ($3E,$02). These messages are sent over a special functional CAN id. The tester present interval is taken from the KWP2000 component's parameter TesterPresentInterval.
It is necessary that the stack is complete but offline with a CAN component used as hardware driver for the Mercedes W2xx plugin to be loaded.
The services used are hardcoded to the values as given in the document "DIAGNOSE in den Baureihen 203/209, v2.1".
Other W2xx ECUs use UDS instead of KWP2000 as diagnostic protocol. Although both are quite similar in many ways UDS expects the functional TesterPresent service to be synchronized to the normal communication. Answers to this service may be generated by the ECU. The W2xx plugin is not compatible with the UDS protocol.
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