STM8S datasheet(383/467 Pages) STMICROELECTRONICS

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RM0016

Controller area network (beCAN)

427

23.5

Test modes

Test modes can be selected by the SILM and LBKM bits in the CAN_DGR register. These

bits must be configured while beCAN is in Initialization mode. Once a test mode has been

selected, the INRQ bit in the CAN_MCR register must be reset to enter Normal mode.

23.5.1

Silent mode

The beCAN can be put in Silent mode by setting the SILM bit in the CAN_DGR register.

In Silent mode, the beCAN is able to receive valid data frames and valid remote frames, but

it sends only recessive bits on the CAN bus and it cannot start a transmission. If the beCAN

has to send a dominant bit (ACK bit, overload flag, active error flag), the bit is rerouted

internally so that the CAN Core monitors this dominant bit, although the CAN bus may

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).

Figure 143. beCAN in silent mode

23.5.2

Loop back mode

The beCAN can be set in Loop Back Mode by setting the LBKM bit in the CAN_DGR

messages and stores them (if they pass acceptance filtering) in the FIFO.

Figure 144. beCAN in loop back mode

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 beCAN performs an internal

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

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

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