MC68HC08AZ32A Datasheet, PDF (124/312 Pages) Motorola, Inc – HCMOS Microcontroller Unit

MSCAN08 Controller (MSCAN08)
11.8.1 MSCAN08 Sleep Mode
The CPU can request the MSCAN08 to enter the low-power mode by asserting the SLPRQ bit in the
module configuration register (see Figure 11-7). The time when the MSCAN08 enters sleep mode
depends on its activity:
• If it is transmitting, it continues to transmit until there is no more messages to be transmitted, and
then goes into sleep mode
• If it is receiving, it waits for the end of this message and then goes into sleep mode
• If it is neither transmitting or receiving, it will immediately go into sleep mode
NOTE
The application software must avoid setting up a transmission (by clearing
one or more TXE flags) and immediately request sleep mode (by setting
SLPRQ). It then depends on the exact sequence of operations as to
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 TxCAN pin stays in
recessive state. If RXF = 1, the message can be read and RXF can be cleared. Copying 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 (wakeup) when:
• Bus activity occurs, or
• The MCU clears the SLPRQ bit, or
• The MCU sets the SFTRES bit
MSCAN08 RUNNING
MCU
SLPRQ = 0
or MSCAN08
SLPAK = 0
MCU
MSCAN08 SLEEPING
SLPRQ = 1
SLPAK = 1
SLEEP REQUEST
SLPRQ = 1
SLPAK = 0
MSCAN08
Figure 11-7. Sleep Request/Acknowledge Cycle
NOTE
The MCU cannot clear the SLPRQ bit before the MSCAN08 is in sleep
mode (SLPAK = 1).
MC68HC08AZ32A Data Sheet, Rev. 2
124
Freescale Semiconductor