RM0016 Controller area network (beCAN)
Doc ID 14587 Rev 8 365/449
Figure 141. beCAN operating modes
23.4 Operating modes
beCAN has three main operating modes: Initialization, Normal and Sleep. After a
hardware reset, beCAN is in sleep mode to reduce power consumption. The software
requests beCAN to enter Initialization or Sleep mode by setting the INRQ or SLEEP bits in
the CAN_MCR register. Once the mode has been entered, beCAN confirms it by setting the
INAK or SLAK bits in the CAN_MSR register. When neither INAK nor SLAK are set, beCAN
is in Normal mode. Before entering Normal mode beCAN always has to synchronize on
the CAN bus. To synchronize, beCAN waits until the CAN bus is idle, this means 11
consecutive recessive bits have been monitored on CANRX.
23.4.1 Initialization mode
The software initialization can be done while the hardware is in Initialization mode. To enter
this mode the software sets the INRQ bit in the CAN_MCR register and waits until the
hardware has confirmed the request by setting the INAK bit in the CAN_MSR register.
To leave Initialization mode, the software clears the INQR bit. beCAN has exit Initialization
mode once the INAK bit has been cleared by hardware. However the Rx line has to be in
recessive state to leave this mode.
While in Initialization mode, all message transfers to and from the CAN bus are stopped and
the status of the CAN bus output CANTX is recessive (high).
Entering Initialization Mode does not change any of the configuration registers.
To initialize the CAN Controller, software has to set up the Bit Timing registers and the filter
banks. If a filter bank is not used, it is recommended to leave it non active (leave the
corresponding FACT bit in the CAN_FCRx register cleared).
Sleep
Initialization
Normal
Reset
SLAK = 1
INAK = 0
SLAK = 0
INAK = 1
SLAK = 0
INAK = 0
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