STM8S datasheet(396/467 Pages) STMICROELECTRONICS

396 / 467 page

Controller area network (beCAN)

RM0016

396/467

DocID14587 Rev 14

23.6.5

Error management

The error management as described in the CAN protocol is handled entirely by hardware

using a Transmit Error Counter (CAN_TECR register) and a Receive Error Counter

(CAN_RECR register), which get incremented or decremented according to the error

condition. For detailed information about TEC and REC management, please refer to the

CAN standard.

Both of them may be read by software to determine the stability of the network.

Furthermore, the CAN hardware provides detailed information on the current error status in

CAN_ESR register. By means of CAN_EIER register and ERRIE bit in CAN_IER register,

the software can configure the interrupt generation on error detection in a very flexible way.

Bus-Off recovery

The Bus-Off state is reached when TEC is greater then 255, this state is indicated by BOFF

bit in CAN_ESR register. In Bus-Off state, the beCAN is no longer able to transmit and

receive messages.

Depending on the ABOM bit in the CAN_MCR register beCAN will recover from Bus-Off

(become error active again) either automatically or on software request. But in both cases

the beCAN has to wait at least for the recovery sequence specified in the CAN standard

(128 x 11 consecutive recessive bits monitored on CANRX).

If ABOM is set, the beCAN will start the recovering sequence automatically after it has

entered Bus-Off state.

If ABOM is cleared, the software must initiate the recovering sequence by requesting

beCAN to enter initialization mode. Then beCAN starts monitoring the recovery sequence

when the beCAN is requested to leave the initialization mode.

Note:

In initialization mode, beCAN does not monitor the CANRX signal, therefore it cannot

complete the recovery sequence. To recover, beCAN must be in normal mode.

Figure 153. CAN error state diagram

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