AN2628

Interrupt sources and identification

5/27

In summary: To enable CAN interrupt to the CPU, set bit IE in the CAN control register,

corresponding enable bit in the XIRxSEL register (x = 0, 3 for CAN1, x = 1, 3 for CAN2) and

bit XPxIE in the X-peripherals interrupt control register XPxIC. Please refer to Appendix A:

Register description.

1.2

Individual interrupt sources

The CAN controller distinguishes three different individual interrupt sources:

●

Status interrupts

●

Error interrupts

●

Message-specific interrupts

1.2.1

Status interrupts

Status interrupts are generated after a status change of the CAN modules is indicated by

the flags in the status register. Status interrupts are enabled by setting bit SIE in the control

register.

Status interrupts are caused by:

●

Successful transmission from the CAN modules (TxOK is set) of any message from

message objects

●

Reception of a message on the CAN bus - RxOK is set after an acknowledge of a CAN

frame from the CAN module - this CAN frame may not correspond to any message

object identifier.

●

Occurrence of an error on the CAN bus during a message transfer (LEC bit field is

updated); this error may not come from the CAN module itself but has at least been

detected by the CAN modules. LEC code 7 is not used and may be written to 7 by the

CPU to check for updates.

TxOK, RxOK, LEC can be read from the status register.

Note:

Enabling the Status Change Interrupt causes an interrupt to the CPU every time a message

is acknowledged on the CAN bus. For this reason, Status Change Interrupt should be

disabled in most applications except where a close monitor on the bus activity is required

(for example, after an early warning).

1.2.2

Error interrupts

Error Interrupts are generated once predefined error conditions are reached. Error interrupts

are enabled by setting bit EIE in the control register. Error interrupts are caused by:

●

Warning status (EWarn is set) indicating that at least one of the error counters has

reached the error warning limit of 96

●

Bus-off (BOff is set) indicating that the CAN controller is in bus-off state

EWarn and BOff can be read from the status register.