MC912DG128ACPVE Datasheet, PDF (339/478 Pages) Freescale Semiconductor, Inc – Upward compatible with M68HC11 instruction set

Freescale Semiconductor, Inc.
MSCAN Controller
Low Power Modes
18.8.1 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
18-6). The time when the msCAN12 will then enter SLEEP mode
depends on its current activity:
• If there are 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
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 will then depend on the exact sequence of
operations whether the msCAN12 will start transmitting or go 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. Clocks to allow register accesses will still run. The TxCAN
pin will stay in recessive state. If RXF=1, the message can be read and
RXF can be cleared. However, if the msCAN12 is in bus-off state, it stops
counting 128*11 consecutive recessive bits due to the stopped clocks.
Likewise, copying of RxBG into RxFG will not take place while in sleep
mode. It is possible to access the transmit buffers and to clear the TXE
flags. No message abort will take place while in sleep mode.
The msCAN12 will leave SLEEP mode (wake-up) when
• bus activity occurs or
• the MCU clears the SLPRQ bit or
• the MCU sets SFTRES.
MC68HC912DT128A — Rev 4.0
MOTOROLA
MSCAN Controller
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Technical Data
339