16-20
MPC561/MPC563 Reference Manual
MOTOROLA
Special Operating Modes
To exit low-power stop mode:
Reset the TouCAN either by asserting one of the IMB3 reset lines or by asserting the
SOFTRST bit CANMCR
Clear the STOP bit in CANMCR
The TouCAN module can optionally exit low-power stop mode via the self wake
mechanism. If the SELFWAKE bit in CANMCR was set at the time the TouCAN
entered stop mode, then upon detection of a recessive to dominant transition on the
CAN bus, the TouCAN clears the STOP bit in CANMCR and its clocks begin
running.
When the TouCAN is in low-power stop mode, a recessive to dominant transition on the
CAN bus causes the WAKEINT bit in the error and status register (ESTAT) to be set. This
event generates an interrupt if the WAKEMSK bit in CANMCR is set.
Consider the following notes regarding low-power stop mode:
When the self wake mechanism is activated, the TouCAN tries to receive the frame
that woke it up. (It assumes that the dominant bit detected is a start-of-frame bit.) It
will not arbitrate for the CAN bus at this time.
If the STOP bit is set while the TouCAN is in the bus off state, then the TouCAN
enters low-power stop mode and stops counting recessive bit times. The count
continues when STOP is cleared.
To place the TouCAN in low-power stop mode with the self wake mechanism
engaged, write to CANMCR with both STOP and SELFWAKE set, and then wait
for the TouCAN to set the STOPACK bit.
To take the TouCAN out of low-power stop mode when the self wake mechanism is
enabled, write to CANMCR with both STOP and SELFWAKE clear, and then wait
for the TouCAN to clear the STOPACK bit.
The SELFWAKE bit should not be set after the TouCAN has already entered
low-power stop mode.
If both STOP and SELFWAKE are set and a recessive to dominant edge
immediately occurs on the CAN bus, the TouCAN may never set the STOPACK bit,
and the STOP bit will be cleared.
To prevent old frames from being sent when the TouCAN awakes from low-power
stop mode via the self wake mechanism, disable all transmit sources, including
transmit buffers configured for remote request responses, before placing the
TouCAN in low-power stop mode.
If the TouCAN is in debug mode when the STOP bit is set, the TouCAN assumes
that debug mode should be exited. As a result, it tries to synchronize with the CAN
bus, and only then does it await the conditions required for entry into low-power stop
mode.