MC908AS60ACFU Datasheet, PDF (277/414 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Low Power Modes
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 MSCAN08 stops its
internal clocks. However, clocks to allow register accesses still run. If the MSCAN08 is in buss-off state,
it stops counting the 128*11 consecutive recessive bits due to the stopped clocks. The TxCAN pin stays
in recessive state. If RXF=1, the message can be read and RXF can be cleared. Copying of RxGB into
RxFG doesn’t 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 MSCAN08 leaves Sleep mode (wake-up) when:
• bus activity occurs or
• the MCU clears the SLPRQ bit or
• the MCU sets the SFTRES bit
NOTE
The MCU cannot clear the SLPRQ bit before the MSCAN08 is in Sleep
mode (SLPAK=1).
After wake-up, the MSCAN08 waits for 11 consecutive recessive bits to synchronize to the bus. As a
consequence, if the MSCAN08 is woken-up by a CAN frame, this frame is not received. The receive
message buffers (RxFG and RxBG) contain messages if they were received before Sleep mode was
entered. All pending actions are executed upon wake-up: copying of RxBG into RxFG, message aborts
and message transmissions. If the MSCAN08 is still in bus-off state after Sleep mode was left, it continues
counting the 128*11 consecutive recessive bits.
23.8.2 MSCAN08 Soft Reset Mode
In Soft Reset mode, the MSCAN08 is stopped. Registers can still be accessed. This mode is used to
initialize the module configuration, bit timing and the CAN message filter. See 23.13.1 MSCAN08 Module
Control Register 0 for a complete description of the Soft Reset mode.
When setting the SFTRES bit, the MSCAN08 immediately stops all ongoing transmissions and
receptions, potentially causing CAN protocol violations.
NOTE
The user is responsible to take care that the MSCAN08 is not active when
Soft Reset mode is entered. The recommended procedure is to bring the
MSCAN08 into Sleep mode before the SFTRES bit is set.
23.8.3 MSCAN08 Power Down Mode
The MSCAN08 is in Power Down mode when the CPU is in Stop mode.
When entering the Power Down mode, the MSCAN08 immediately stops all ongoing transmissions and
receptions, potentially causing CAN protocol violations.
NOTE
The user is responsible to take care that the MSCAN08 is not active when
Power Down mode is entered. The recommended procedure is to bring the
MSCAN08 into Sleep mode before the STOP instruction is executed.
To protect the CAN bus system from fatal consequences of violations to the above rule, the MSCAN08
drives the TxCAN pin into recessive state.
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
Freescale Semiconductor
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