Message Transmission - NEC V850E/RS1 User Manual

16.10 Message Transmission

16.10.1 Message transmission
In all the operation modes, if the TRQ bit is set to 1 in a message buffer that satisfies the following con-
ditions, the message buffer that is to transmit a message is searched.
• Used as a message buffer
• Set as a transmit message buffer
• Ready for transmission
The CAN system is a multi-master communication system. In a system like this, the priority of message
transmission is determined based on message identifiers (IDs). To facilitate transmission processing by
software when there are several messages awaiting transmission, the CAN module uses hardware to
check the ID of the message with the highest priority and automatically identifies that message. This
eliminates the need for software-based priority control.
Transmission priority is controlled by the identifier (ID).
Message No.
After the transmit message search, the transmit message with the highest priority of the transmit mes-
sage buffers that have a pending transmission request (message buffers with the TRQ bit set to 1 in
advance) is transmitted.
If a new transmission request is set, the transmit message buffer with the new transmission request is
compared with the transmit message buffer with a pending transmission request. If the new transmis-
sion request has a higher priority, it is transmitted, unless transmission of a message with a low priority
has already started. If transmission of a message with a low priority has already started, however, the
new transmission request is transmitted later. The highest priority is determined according to the follow-
ing rules.
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(MA0 bit of CnMCONFm register set to 1B.)
(MT[2:0] bits of CnMCONFm register set to 000B.)
(RDY bit of CnMCTRLm register set to 1.)
Figure 16-52: Message Processing Example
Message waiting to be transmitted
0
1 ID = 120H
2 ID = 229H
3
4
5 ID = 223H
6 ID = 023H
7
8 ID = 123H
9
Chapter 16 FCAN Controller
The CAN module transmits messages in the following sequence.
1. Message 6
2. Message 1
3. Message 8
4. Message 5
5. Message 2
User's Manual U16702EE3V2UD00