Normal Mode; Sleep Mode (Low Power); Test Mode; Figure 193. Bxcan Operating Modes - ST STM32F102 Series Reference Manual

RM0008
To initialize the registers associated with the CAN filter banks (mode, scale, FIFO
assignment, activation and filter values), software has to set the FINIT bit (CAN_FMR). Filter
initialization also can be done outside the initialization mode.
Note: When FINIT=1, CAN reception is deactivated.
The filter values also can be modified by deactivating the associated filter activation bits (in
the CAN_FA1R register).
If a filter bank is not used, it is recommended to leave it non active (leave the corresponding
FACT bit cleared).
21.3.2

Normal mode

Once the initialization has been done, the software must request the hardware to enter
Normal mode, to synchronize on the CAN bus and start reception and transmission.
Entering Normal mode is done by clearing the INRQ bit in the CAN_MCR register and
waiting until the hardware has confirmed the request by clearing the INAK bit in the
CAN_MSR register. Afterwards, the bxCAN synchronizes with the data transfer on the CAN
bus by waiting for the occurrence of a sequence of 11 consecutive recessive bits (≡ Bus
Idle) before it can take part in bus activities and start message transfer.
The initialization of the filter values is independent from Initialization Mode but must be done
while the filter is not active (corresponding FACTx bit cleared). The filter scale and mode
configuration must be configured before entering Normal Mode.
21.3.3

Sleep mode (low power)

To reduce power consumption, bxCAN has a low-power mode called Sleep mode. This
mode is entered on software request by setting the SLEEP bit in the CAN_MCR register. In
this mode, the bxCAN clock is stopped, however software can still access the bxCAN
mailboxes.
If software requests entry to initialization mode by setting the INRQ bit while bxCAN is in
Sleep mode, it must also clear the SLEEP bit.
bxCAN can be woken up (exit Sleep mode) either by software clearing the SLEEP bit or on
detection of CAN bus activity.
On CAN bus activity detection, hardware automatically performs the wakeup sequence by
clearing the SLEEP bit if the AWUM bit in the CAN_MCR register is set. If the AWUM bit is
cleared, software has to clear the SLEEP bit when a wakeup interrupt occurs, in order to exit
from Sleep mode.
Note: If the wakeup interrupt is enabled (WKUIE bit set in CAN_IER register) a wakeup interrupt
will be generated on detection of CAN bus activity, even if the bxCAN automatically performs
the wakeup sequence.
After the SLEEP bit has been cleared, Sleep mode is exited once bxCAN has synchronized
with the CAN bus, refer to
once the SLAK bit has been cleared by hardware.
21.3.4

Test mode

Test mode can be selected by the SILM and LBKM bits in the CAN_BTR register. These bits
must be configured while bxCAN is in Initialization mode. Once test mode has been
selected, the INRQ bit in the CAN_MCR register must be reset to enter Normal mode.
Figure 193: bxCAN operating
Controller area network (bxCAN)
modes. The Sleep mode is exited
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