MC68HC08GZ32 Datasheet, PDF (126/320 Pages) Freescale Semiconductor, Inc – Microcontrollers

MSCAN08 Controller (MSCAN08)
12.8.2 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 12.13.1 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.
12.8.3 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 resulting from violations of the above rule, the
MSCAN08 drives the CAN_TX 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.
12.8.4 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.
12.8.5 Programmable Wakeup Function
The MSCAN08 can be programmed to apply a low-pass filter function to the CAN_RX input line while in
internal sleep mode (see information on control bit WUPM in 12.13.2 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.
12.9 Timer Link
The MSCAN08 will generate a timer signal whenever a valid frame has been received. Because the CAN
specification defines a frame to be valid if no errors occurred before the EOF field has been transmitted
successfully, the timer signal will be generated right after the EOF. A pulse of one bit time is generated.
As the MSCAN08 receiver engine also receives the frames being sent by itself, a timer signal also will be
generated after a successful transmission.
MC68HC08GZ32 Data Sheet, Rev. 3
126
Freescale Semiconductor