Civil Engineering Reference
In-Depth Information
used bus level definitions may be a solution. One concept of using special bus levels
is described in the SAE J2411 standard (Single-Wire CAN). High voltage levels
can lead to a wake-up. The disadvantage of this concept is again the low flexibility
because such pulses are seen globally as a wake-up event. A selective wake-up of
particular ECUs is not possible. Another disadvantage is that due to the higher volt-
age levels, more intense EMC emissions are possible which result in worse EMC
characteristics.
2.5.2.4
Variant 4: Bus Messages
Considering the OSI layer 2, the data link layer, special bit patterns can be used
to decode wake-up events. Again, it must be distinguished between two different
scenarios: On the one hand, the microcontroller can overtake the decoding and the
decision if a wake-up sequence occurred. On the other hand, the transceiver can be
added with the functionalities to be able to decode wake-up sequences.
If bit sequences are used like the content of two data bytes of a frame, the imple-
mentation effort inside the transceiver would be relatively low, but the disadvantage
would be that due to application-dependent unknown data occurrence unwanted
wake-ups can occur. To avoid this disadvantage the CAN ID should be consid-
ered as well. Thus, whole CAN messages should be considered to decode particular
wake-up events for particular ECUs.
Through the consideration of whole CAN messages, the required flexibility is
given and the risk of unwanted wake-ups is avoided. For a solution inside a trans-
ceiver, this implies that the transceiver functionality must be enhanced with de-
coding functions regarding the ISO 11898 as well as configuration functions (with
ID and data content) to configure the wake-up frame (WUF) of the transceiver.
Difficulties exist in the internal clock generation for sampling the CAN bus be-
cause external clock generation components would need additional transceiver pins
(backward compatibility) and are expensive.
Actually, the solution of enhancing the transceiver functions is favoured. Be-
cause the previously mentioned necessary requirements for partial networking with
selective wake-up can be fulfilled with the transceiver haven CAN frame decoding
functionalities, this variant is described in more detail in the following section.
2.5.3
Partial Networking (Infineon)
In a normal CAN network, all CAN nodes are permanently active when the CAN
communication is running, independent of the fact that the ECU is used or not.
However, many applications are not used all the time, and these ECUs can be
switched off to reduce the power consumption. A solution for such a realization
must fulfil the following criteria:
