UPD78F0838 Renesas Electronics Corporation., UPD78F0838 Datasheet - Page 614

• Manufacturer Part Number: UPD78F0838
• Description: 8-bit Single-chip Microcontrollers
• Manufacturer: Renesas Electronics Corporation.

15.10 Message Transmission
15.10.1 Message transmission
message buffer that is to transmit a message is searched.
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.
that have a pending transmission request (message buffers with the TRQ bit set to 1 in advance) is transmitted.
with the transmit message buffer with a pending transmission request. If the new transmission 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. To solve
this priority inversion effect, the software can perform a transmission abort request for the lower priority message.
The highest priority is determined according to the following rules.
612
In all the operation modes, if the TRQ bit is set to 1 in a message buffer that satisfies the following conditions, the
- Used as a message buffer
- Set as a transmit message buffer
- Ready for transmission
The CAN system is a multi-master communication system.
Transmission priority is controlled by the identifier (ID).
After the transmit message search, the transmit message with the highest priority of the transmit message buffers
If a new transmission request is set, the transmit message buffer with the new transmission request is compared
(MA0 bit of C0MCONFm register set to 1B.)
(RDY bit of C0MCTRLm register set to 1.)
(MT [2:0] bits of C0MCONFm register set to 000B.)
Message No.
0
1
2
3
4
5
6
7
8
9
Message waiting to be transmitted
ID = 120H
ID = 229H
ID = 223H
ID = 023H
ID = 123H
Figure 15-31. Message Processing Example
Preliminary User’s Manual U19748EJ1V0UD
CHAPTER 15 CAN 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
In a system like this, the priority of message