
Chapter 10 Freescale’s Scalable Controller Area Network (S12MSCANV2)
Freescale Semiconductor
MC9S12C-Family / MC9S12GC-Family
Rev 01.23
337
The MSCAN is able to leave sleep mode (wake up) only when:
CAN bus activity occurs and WUPE = 1
or
the CPU clears the SLPRQ bit
NOTE
The CPU cannot clear the SLPRQ bit before sleep mode (SLPRQ = 1 and
SLPAK = 1) is active.
After wake-up, the MSCAN waits for 11 consecutive recessive bits to synchronize to the CAN bus. As a
consequence, if the MSCAN is woken-up by a CAN frame, this frame is not received.
Thereceivemessagebuffers(RxFGandRxBG)containmessagesiftheywerereceivedbeforesleepmode
was entered. All pending actions will be executed upon wake-up; copying of RxBG into RxFG, message
aborts and message transmissions. If the MSCAN remains in bus-off state after sleep mode was exited, it
continues counting the 128 occurrences of 11 consecutive recessive bits.
Figure 10-45. Simplified State Transitions for Entering/Leaving Sleep Mode
Wait
for Idle
Idle
Tx/Rx
Message
Active
CAN Activity
CAN Activity &
SLPRQ
Sleep
SLPRQ
StartUp
(CAN Activity & WUPE) |
CAN Activity
(CAN Activity & WUPE) | SLPRQ
CAN Activity
CAN Activity
CAN Activity &
SLPRQ
CAN Activity