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FlexCAN Module
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
1393
The module enters this mode when CR[LOM] is asserted. In this mode, transmission is disabled,
all error counters are frozen and the module operates in a CAN Error Passive mode. Only messages
acknowledged by another CAN station will be received. If FlexCAN detects a message that has not
been acknowledged, it will flag a BIT0 error (without changing the REC), as if it was trying to
acknowledge the message.
•
Loop-Back Mode:
The module enters this mode when CR[LPB] is asserted. In this mode, FlexCAN performs an
internal loop back that can be used for self test operation. The bit stream output of the transmitter
is internally fed back to the receiver input. The Rx CAN input pin is ignored and the Tx CAN
output goes to the recessive state (logic ‘1’). FlexCAN behaves as it normally does when
transmitting and treats its own transmitted message as a message received from a remote node. In
this mode, FlexCAN ignores the bit sent during the ACK slot in the CAN frame acknowledge field
to ensure proper reception of its own message. Both transmit and receive interrupts are generated.
•
Module Disable Mode:
This low power mode is entered when the MDIS bit in the MCR Register is asserted by the CPU.
When disabled, the module sends a request to disable the clocks to the CAN Protocol Interface and
Message Buffer Management sub-modules. Exit from this mode is done by negating MCR[MDIS].
See
Section 32.5.9.2, Module Disable Mode
, for more information.
•
Stop Mode:
This low power mode is entered when Stop Mode is requested at MCU level. When in Stop Mode,
the module puts itself in an inactive state and then informs the CPU that the clocks can be shut
down globally. Exit from this mode happens when the Stop Mode request is removed or when
activity is detected on the CAN bus and the Self Wake Up mechanism is enabled. See
, for more information.
32.3
External signal description
32.3.1
Overview
The FlexCAN module has two I/O signals connected to the external MCU pins. These signals are
summarized in
and described in more detail in the next subsections.
Table 32-1. FlexCAN signals
Signal name
1
1
The actual MCU pins may have different names.
Direction
Description
CAN_
x
_RX
Input
CAN receive pin
CAN_
x
_TX
Output
CAN transmit pin
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