Loop Back Mode; Loop Back Combined With Silent Mode; Figure 224. Bxcan In Silent Mode; Figure 225. Bxcan In Loop Back Mode - ST STM32F101 series Reference Manual

Advanced arm-based 32-bit mcus

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Controller area network (bxCAN)

remain in recessive state. Silent mode can be used to analyze the traffic on a CAN bus

without affecting it by the transmission of dominant bits (Acknowledge Bits, Error Frames).

Loop back mode

The bxCAN can be set in Loop Back Mode by setting the LBKM bit in the CAN_BTR

messages and stores them (if they pass acceptance filtering) in a Receive mailbox.

This mode is provided for self-test functions. To be independent of external events, the CAN

Core ignores acknowledge errors (no dominant bit sampled in the acknowledge slot of a

data / remote frame) in Loop Back Mode. In this mode, the bxCAN performs an internal

feedback from its Tx output to its Rx input. The actual value of the CANRX input pin is

disregarded by the bxCAN. The transmitted messages can be monitored on the CANTX pin.

It is also possible to combine Loop Back mode and Silent mode by setting the LBKM and

SILM bits in the CAN_BTR register. This mode can be used for a "Hot Selftest", meaning the

bxCAN can be tested like in Loop Back mode but without affecting a running CAN system

connected to the CANTX and CANRX pins. In this mode, the CANRX pin is disconnected

from the bxCAN and the CANTX pin is held recessive.

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