MC68HC08GZ32 Datasheet, PDF(125/320 Page) Freescale Semiconductor, Inc – Microcontrollers

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MC68HC08GZ32 Datasheet, PDF (125/320 Pages) Freescale Semiconductor, Inc – Microcontrollers

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MCU

or MSCAN08

MSCAN08 RUNNING

SLPRQ = 0

SLPAK = 0

Low-Power Modes

MCU

MSCAN08 SLEEPING

SLPRQ = 1

SLPAK = 1

SLEEP REQUEST

SLPRQ = 1

SLPAK = 0

MSCAN08

Figure 12-7. Sleep Request/Acknowledge Cycle

NOTE

The application software must avoid setting up a transmission (by clearing

or more TXE flags) and immediately request sleep mode (by setting

SLPRQ). It then depends on the exact sequence of operations whether

MSCAN08 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 MSCAN08 stops its

internal clocks. However, clocks to allow register accesses still run. If the MSCAN08 is in bus-off state, it

stops counting the 128*11 consecutive recessive bits due to the stopped clocks. The CANTX pin stays in

recessive state. If RXF = 1, the message can be read and RXF can be cleared. Copying of RxGB into

RxFG doesnât 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 (wakes-up) when:

â¢ Bus activity occurs, or

â¢ The MCU clears the SLPRQ bit, or

â¢ The MCU sets the SFTRES bit

NOTE

The MCU cannot clear the SLPRQ bit before the MSCAN08 is in sleep

mode (SLPAK=1).

After wakeup, 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 wakeup: 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.

MC68HC08GZ32 Data Sheet, Rev. 3

Freescale Semiconductor

125

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