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• Listen-Only mode:
The module enters this mode when the LOM bit in the Control 1 Register 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 the LPB bit in the Control 1 Register 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.
For low-power operation, the FlexCAN module has:
• Module Disable mode:
This low-power mode is entered when the MDIS bit in the MCR Register is asserted
by the CPU and the LPM_ACK is asserted by the FlexCAN. When disabled, the
module requests to disable the clocks to the CAN Protocol Engine and Controller
Host Interface sub-modules. Exit from this mode is done by negating the MDIS bit in
the MCR Register. See Module Disable mode for more information.
• Stop mode:
This low power mode is entered when Stop mode is requested at MCU level and the
LPM_ACK bit in the MCR Register is asserted by the FlexCAN. 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 Stop mode for more information.
Chapter 45 CAN (FlexCAN)
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
Freescale Semiconductor, Inc.
Preliminary
1107
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