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MPC563XM Reference Manual, Rev. 1
Freescale Semiconductor
1313
Preliminary—Subject to Change Without Notice
The sensitivity to CAN bus activity can be modified by applying a low-pass filter function to the Rx CAN
input line while in Stop Mode. See the WAK_SRC bit in
Section 28.4.4.1, “Module Configuration Register
. This feature can be used to protect FlexCAN from waking up due to short glitches on the CAN
bus lines. Such glitches can result from electromagnetic interference within noisy environments.
NOTE
Not all MCUs are equipped with the low-pass filter. Consult the specific
MCU documentation to determine if the low-pass filter is available and to
determine its electrical parameters.
28.5.10 Interrupts
The module can generate up to 70 interrupt sources (64 interrupts due to message buffers and 6 interrupts
due to Ored interrupts from MBs, Bus Off, Error, Tx Warning, Rx Warning and Wake Up). The number of
actual sources depends on the configured number of Message Buffers.
Each one of the message buffers can be an interrupt source, if its corresponding IMASK bit is set. There
is no distinction between Tx and Rx interrupts for a particular buffer, under the assumption that the buffer
is initialized for either transmission or reception. Each of the buffers has assigned a flag bit in the IFLAG
Registers. The bit is set when the corresponding buffer completes a successful transmission/reception and
is cleared when the CPU writes it to ‘1’ (unless another interrupt is generated at the same time).
NOTE
It must be guaranteed that the CPU only clears the bit causing the current
interrupt. For this reason, bit manipulation instructions (BSET) must not be
used to clear interrupt flags. These instructions may cause accidental
clearing of interrupt flags which are set after entering the current interrupt
service routine.
If the Rx FIFO is enabled (bit FEN on MCR set), the interrupts corresponding to MBs 0 to 7 have a
different behavior. Bit 7 of the IFLAG1 becomes the “FIFO Overflow” flag; bit 6 becomes the FIFO
Warning flag, bit 5 becomes the “Frames Available in FIFO flag” and bits 4-0 are unused. See
Section 28.4.4.12, “Interrupt Flags 1 Register (IFLAG1),”
for more information.
A combined interrupt for all MBs is also generated by an Or of all the interrupt sources from MBs. This
interrupt gets generated when any of the MBs generates an interrupt. In this case the CPU must read the
IFLAG Registers to determine which MB caused the interrupt.
The other 5 interrupt sources (Bus Off, Error, Tx Warning, Rx Warning and Wake Up) generate interrupts
like the MB ones, and can be read from the Error and Status Register. The Bus Off, Error, Tx Warning and
Rx Warning interrupt mask bits are located in the Control Register, and the Wake-Up interrupt mask bit is
located in the MCR.
28.5.11 Bus Interface
The CPU access to FlexCAN registers are subject to the following rules:
•
Read and write access to supervisor registers in User Mode results in access error.