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2.6 Wakeup
The transition from the low power state to a powered state of the Bus Drivers is called
Wakeup. This transition can be initialized by the Communication Controller, or by the bus
itself, if the Bus Driver receives Wakeup Patterns. For the latter, the Bus Driver has to
identify at least two Wakeup Symbols.
Not every ECU on a network is allowed to send Wakeup Patterns. If a ECU has the
permission to send such patterns, it is called a Wakeup Node, and may send 2 to 63 Wakeup
Symbols.
A Wakeup Symbol is defined (see Figure 2.17) as a Data_0 phase followed by an Idle phase.
To ensure the Bus Driver can identify these phases, the following timing constraints have to
be obeyed: dWU 01 , dWU Idle1 , dWU 02 , dWU Idle2 > 4µs und dWU < 48µs.
Figure 2.17 Wakeup Pattern [EPLS06]
A network may only contain up to 3 Wakeup Nodes, since an overlap of several Wakeup
Patterns could prevent a correct detection, see Table 2.2.
Table 2.2 Wakeup Pattern Detection [EPLS06]
Name Description Min Max Unit
dWU 0Detect Acceptable limits for detecting a 1 4 µs
Data_0 phase.
dWU IdleDetect Acceptable limits for detecting an 1 4 µs
Idle phase.
dWU Timeout Acceptable limits for detecting a
Wakeup Pattern
48 140 µs
However, it is possible to define different Wakeup Nodes for channels A and B. This opens
up additional possibilities for the network designer, as seen in the example in Figure 2.18.
Here, the network on channel A is woken up by ECU1 due to a local event, while channel B is
still asleep.
Bäurle 12.10.2012