Freescale Semiconductor, Inc.
MSCAN Controller
17.8.1 msCAN12 SLEEP Mode
The CPU can request the msCAN12 to enter this low-power mode by
asserting the SLPRQ bit in the Module Configuration Register (see
Figure 17-6). The time when the msCAN12 enters Sleep Mode depends
on its activity:
• If one or more message buffers are scheduled for transmission
(TXEx = 0), the msCAN will continue to transmit until all transmit
message buffers are empty (TXEx = 1, transmitted successfully or
aborted) and then goes into Sleep Mode
• If it is receiving, it continues to receive and goes into Sleep Mode
as soon as the CAN bus next becomes idle
• If it is neither transmitting nor receiving, it will immediately go into
Sleep Mode
NOTE: The application software must avoid setting up a transmission (by
clearing one or more TXE flag(s)) and immediately request Sleep Mode
(by setting SLPRQ). It then depends on the exact sequence of
operations whether the msCAN12 starts transmitting or goes into Sleep
Mode directly.
During Sleep Mode, the SLPAK flag is set. The application software
should use SLPAK as a handshake indication for the request (SLPRQ)
to go into Sleep Mode. When in Sleep Mode, the msCAN12 stops its
internal clocks. However, clocks to allow register accesses still run. If the
msCAN12 is in bus-off state, it stops counting the 128*11 consecutive
recessive bits due to the stopped clock. The TxCAN pin stays in
recessive state. If RXF=1, the message can be read and RXF can be
cleared. Copying of RxBG into RxFG does not take place while in Sleep
Mode. It is possible to access the transmit buffers and to clear the TXE
flags. No message abort takes place while in sleep mode.
The msCAN12 leaves Sleep mode (wake-up) when
• bus activity occurs or
• the MCU clears the SLPRQ bit or
• the MCU sets SFTRES.
Technical Data
MC68HC912DG128 — Rev 3.0
MSCAN Controller
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