RM0046 FlexCAN
Doc ID 16912 Rev 5 533/936
● Independent of the transmission medium (an external transceiver is assumed)
● Short latency time due to an arbitration scheme for high-priority messages
● Low power modes, with programmable wake up
22.1.3 Modes of operation
The FlexCAN module has four functional modes: Normal mode (User and Supervisor),
Freeze mode, Listen-Only Mode, and Loop-Back mode. There are also these low power
modes: Disable mode and Stop mode, and a Test mode.
● Normal mode (User or Supervisor)
In Normal mode, the module operates receiving and/or transmitting message frames,
errors are handled normally and all the CAN Protocol functions are enabled. User and
Supervisor modes differ in the access to some restricted control registers.
● Freeze mode
It is enabled when the FRZ bit in the Module Configuration Register (MCR) is asserted.
If enabled, Freeze Mode is entered when the HALT bit in the MCR is set or when Debug
Mode is requested at MCU level. In this mode, no transmission or reception of frames is
done and synchronicity to the CAN bus is lost. See Section , “Freeze mode for more
information.
● Listen-Only mode
The module enters this mode when the LOM bit in the Control Register is asserted. In
this mode, transmission is disabled, all error counters are frozen and the module
operates in a CAN Error Passive mode [Ref. 1]. 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 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.
● Module Disable mode
This low power mode is entered when the MDIS bit in the MCR is asserted. When
disabled, the module shuts down the clocks to the CAN Protocol Interface and
Message Buffer Management submodules. Exit from this mode is done by negating the
MDIS bit in the MCR. See Section , “Module disable mode for more information.
● Stop mode
This low power mode is entered when Stop mode is requested at device 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. See Section , “Stop mode for more information.
To Next Page
Loading...
