Physical Layer - CAN System Engineering - page 84

Fig. 2.35 Simulated differential bus voltages
well as the digital RxD signals at the transceiver. Figure 2.35 depicts the differential
voltage for two of the ECUs. Using Saber's post-processing capabilities, measure-
ments such as slew rate can be easily extracted with a single mouse click.
Moreover, the simulation performed in Saber affords the developer a deeper in-
sight into the CAN topology in order to evaluate the robustness of the physical layer
implementation. Aside from the analogue bus signals, it is possible to integrate a
digital CAN controller model into the simulation to take into account the bit tim-
ing behaviour. Saber's model library includes a simplified CAN controller model
which is optimized for performing signal integrity analysis of the physical layer
implementation. The origins of this model started with an initial specification from
Volkswagen in Germany. The model contains the following features:
• Transmit and receive functionality
• Arbitration
• Hard and soft synchronization
• Acknowledgement
• Bit timing register settings
In addition to the optimization of the signal integrity mentioned previously, the
model allows for exploration of the impact of the controller configuration on the
overall system behaviour. Figure 2.36 gives an overview of the available post-pro-
cessing data using the CAN controller model in Saber.
By modelling the bit timing, the developer can determine exactly the time be-
tween the sample point and the critical transition area after the change of the digital
signal. If the sample point is too close to the critical ringing area, the developer can
apply changes to the controller software and adjust the location of the sample point
or fix the problem in the hardware topology. The first solution is often easier to