TTCAN | User’s Manual | Revision 1.6 |
manual_about.fm
reset or configuration, giving no acknowledge). When it reaches Initial_Watch_Trigger (not part of the Trigger List, defined as maximum of Cycle Time), the attempted transmission is aborted, IWT in the Interrupt Vector register is set, the FSE is frozen, and the Cycle Time will become invalid, but the node will still be able to take part in CAN bus communication (to give acknowledge or to send error flags). Resetting IWT will restart the FSE and Cycle Time, the FSE will not be restarted by the reception of a Reference Message.
When a Potential Time Master reaches the Watch_Triggers after it has received any message but the Reference Message, it will assume a Fatal Error (Error Level 3), set WTr in the Interrupt Vector register, switch off its CAN bus output, and enter the Bus Monitoring Mode. In the Bus Monitoring Mode, it is still able to receive messages, but it cannot send any dominant bits (e.g. cannot give acknowledge). The Fatal Error state can be left via a
When no error is encountered during initialisation, the first Reference Message will put SyncST to Synchronising and the second will put it (depending on its Next_is_Gap bit) into In_Schedule or In_Gap, enabling all Tx_Triggers and Rx_Triggers.
A Potential Time Master will be in MState Current Time Master when it was the transmitter of the last Reference Message, else it will be in MState Backup Time Master.
When all Potential Time Masters have finished Configuration, the node with the highest Time Master Priority in the network will become the Current Time Master.
5.3TTCAN Message Handling
5.3.1Message Reception
In TTCAN, the handling of received message is the same as in Event driven CAN Communication, see chapter 4.1.3.1. The message’s MSC will be updated at the message’s Rx_Trigger(s) and gives additional means to check whether the received data arrived on time.
5.3.2 Message Transmission
In TTCAN, the handling of message to be transmitted is similar as in “Event driven CAN Communication”, see chapter 4.1.2. The differences for periodic messages and event driven messages are described in the following sections.
5.3.2.1 Periodic Messages
Neither TxRqst nor Newdat are changed from their preconfigured values. The application program has to update the data regularly and on time, synchronised to the Cycle Time. TTCAN’s CPU interface structure guarantees that no partially updated messages are transmitted. The message’s MSC provides information on the success of the transmission. The transmission may be temporarily disabled by resetting MsgLst or NewDat.
5.3.2.2 Event Driven Messages
The message data may be updated asynchronously to the Cycle Time, the transmission of the event driven message inside an Arbitrating Time Window is requested by setting both TxRqst and NewDat to ‘1’. The actual transmission is started time triggered when Cycle Time reaches the Time_Mark of the Tx_Trigger_Single or Tx_Trigger_Merged configured for the Message Object. Different from “Event driven CAN Communication”, the success of the transmission is indicated when the Message Handler resets NewDat while TxRqst remains unchanged. The MSC of an event driven message is not updated. When the transmission was not successful (lost arbitration or disturbance), it will be repeated next time (one of) its Tx_Trigger(s) become(s) active. When the transmission attempt was inside a Merged Arbitrating Time
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