Stop mode is exited when the CPU resumes the clocks and removes the Stop Mode
request. This can be as a result of the Self Wake mechanism.
In the Self Wake mechanism, if the SLFWAK bit in CAN_MCR Register was set at the
time FlexCAN entered Stop mode, then upon detection of a recessive to dominant
transition on the CAN bus, FlexCAN sets the WAKINT bit in the CAN_ESR Register
and, if enabled by the WAKMSK bit in CAN_MCR, generates a Wake Up interrupt to
the CPU. Upon receiving the interrupt, the CPU should resume the clocks and remove the
Stop mode request. FlexCAN will then wait for 11 consecutive recessive bits to
synchronize to the CAN bus. As a consequence, it will not receive the frame that woke it
up. The following table details the effect of SLFWAK and WAKMSK upon wake-up
from Stop mode. Note that wake-up from Stop mode only works when both bits are
asserted.
After the CAN protocol engine recognizes the negation of the Stop mode request, the
FlexCAN negates the LPMACK bit. FlexCAN will then wait for 11 consecutive
recessive bits to synchronize to the CAN bus. As a consequence, it will not receive the
frame that woke it up.
Table 43-118. Wake-up from Stop Mode
SLFWAK
WAKINT
WAKMSK
MCU
clocks enabled
Wake-up interrupt
generated
0
-
-
No
No
0
-
-
No
No
1
0
0
No
No
1
0
1
No
No
1
1
0
No
No
1
1
1
Yes
Yes
The sensitivity to CAN bus activity can be modified by applying a low-pass filter
function to the Rx CAN input line while in Stop mode. See the WAKSRC bit in in the
description of the Module Configuration Register (CAN_MCR). This feature can be used
to protect FlexCAN from waking up due to short glitches on the CAN bus lines. Such
glitches can result from electromagnetic interference within noisy environments.
43.5.11 Interrupts
The module has many interrupt sources: interrupts due to message buffers and interrupts
due to the ORed interrupts from MBs, Bus Off, Bus Off Done, Error, Wake Up, Tx
Warning, and Rx Warning.
Chapter 43 Flex Controller Area Network (FlexCAN)
KV4x Reference Manual, Rev. 2, 02/2015
Freescale Semiconductor, Inc.
Preliminary
1163
Summary of Contents for freescale KV4 Series
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