CAN Sample-Point Analyzer

Abstract

The purpose of this master thesis project is to develop a method for verifying the sample point position (SPP) of an electronic control unit (ECU). The thesis is performed in two phases; first a theoretical solution of the problem and also a practical implementation. To realize the theory a circuit board were constructed. The solution of the problem is then tested and verified on the design PCB. To be able to validate the test result special test instrument was used such as an oscilloscope with a controller-­‐‑area network (CAN) analyzer module. To analyse the sample point position the method used takes advantage of the built-­‐‑in error detection function, Stuff error. The Stuff error is a mechanism integrated in the CAN protocol and is provoked when it don’t perceive an expected stuff bit in the message sent over the CAN bus. To generate a stuff bit error the bit length of the stuff bit is decreased until the receiver no longer can interpret it. When this occurs an error flag is set and by keeping track of the number of steps that the length has been decreased the sample point position can be calculated. The accuracy of the calculation of the sample point position is within the given limits that have been set for this project. As seen in the report the results are SPP±2% which is close enough to know when data is sampled.