MC68HC08AZ32A Datasheet, PDF (125/312 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Low Power Modes
After wakeup, the MSCAN08 waits for 11 consecutive recessive bits to synchronize to the bus. As a
consequence, if the MSCAN08 is woken 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.
11.8.2 MSCAN08 Soft Reset Mode
In soft reset mode, the MSCAN08 is stopped although registers can still be accessed. This mode is used
to initialize the module configuration, bit timing, and the CAN message filter. See 11.13.1 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.
11.8.3 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.
In power down mode, no registers can be accessed.
MSCAN08 bus activity can wake the MCU from CPU stop/MSCAN08 power-down mode. However, until
the oscillator starts up and synchronization is achieved the MSCAN08 will not respond to incoming data.
11.8.4 CPU Wait Mode
The MSCAN08 module remains active during CPU wait mode. The MSCAN08 will stay synchronized to
the CAN bus and generates transmit, receive, and error interrupts to the CPU, if enabled. Any such
interrupt will bring the MCU out of wait mode.
11.8.5 Programmable Wakeup Function
The MSCAN08 can be programmed to apply a low-pass filter function to the RxCAN input line while in
internal sleep mode (see information on control bit WUPM in 11.13.2 MSCAN08 Module Control Register
1). This feature can be used to protect the MSCAN08 from wakeup due to short glitches on the CAN bus
lines. Such glitches can result from electromagnetic inference within noisy environments.
MC68HC08AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
125