39.6.6.7 Transmit Cancellation

The CAN supports transmit cancellation. This feature is especially intended for gateway applications and AUTOSAR based applications. To cancel a requested transmission from a dedicated Tx Buffer or a Tx Queue Buffer the CPU has to write a ‘1’ to the corresponding bit position (=number of Tx Buffer) of register TXBCR. Transmit cancellation is not intended for Tx FIFO operation.

Successful cancellation is signaled by setting the corresponding bit of register TXBCF to ‘1’.

In case a transmit cancellation is requested while a transmission from a Tx Buffer is already ongoing, the corresponding TXBRP bit remains set as long as the transmission is in progress. If the transmission was successful, the corresponding TXBTO and TXBCF bits are set. If the transmission was not successful, it is not repeated and only the corresponding TXBCF bit is set.

Note: In case a pending transmission is canceled immediately before this transmission could have been started, there follows a short time window where no transmission is started even if another message is also pending in this node. This may enable another node to transmit a message which may have a lower priority than the second message in this node.