Physical Layer - CAN System Engineering - page 113

Fig. 2.51 Generic electronic control unit in active mode
group initiated by the Verband der Automobilindustrie, VDA), an ideas competi-
tion was launched by the German automakers, calling on semiconductor vendors
to present their solutions for the support of this kind of partial network operation
by a transceiver. The results were pooled in a requirement specification docu-
ment [OEM11]. From the very start, however, this VDA working group had the
stated goal to establish an international standard rather than a proprietary solution.
For this reason, experts from automakers and semiconductor vendors worked to-
gether under the roof of the so-called selective wake-up interoperable transceiver
in CAN high-speed (SWITCH) group in order to prepare the standard proposal
ISO/NP 11898-6 “Road vehicles—Controller area network (CAN)—Part 6: High-
speed medium access unit with selective wake-up functionality”. This proposal
has been forwarded to the ISO for decision and is currently in the stage “new
project approved”.
The essential outcome of the standardization efforts of the VDA working group
and the SWITCH group so far is that partial network operation will be realized by
selective wake-up of ECUs in partial network mode with the help of individual
WUFs. The WUF is a valid CAN data frame in accordance with ISO 11898-1.
Figure 2.51 depicts a generic ECU in active mode. A typical current consumption
of such a control unit can be several 100 mA.
The challenge is to minimize the current consumption of such a control unit
while providing for selective wake-up capability via the data bus at the same time.
One reasonable approach involves the implementation of the necessary additional
functions for partial network operation in the transceiver as this device is the link for
the connection between the control unit and the vehicle's data bus. If the transceiver
is supplied directly by the battery in partial network mode, as is common practice
today in sleep mode, all other components of the control unit can be deactivated.
Therefore, this approach is distinguished by higher energy saving potential when
compared to the implementation of partial network operation, for example, in the
microcontroller. The control unit in partial network mode is depicted in Fig. 2.52 ,
indicating inactive functional blocks in grey.
The transceiver now “listens” to the data bus and analyses the bus traffic. Once
the WUF, the individual message for the respective control unit, is detected on the