RL78/F13, F14 CHAPTER 18 CAN INTERFACE (RS-CAN LITE)
R01UH0368EJ0210 Rev.2.10 1390
Dec 10, 2015
18.6 Transmission Functions
There are two types of transmission.
• Transmission using transmit buffers:
Each channel has 4 buffers.
• Transmission using transmit/receive FIFO buffers (transmit mode):
Each channel has one FIFO buffer. Up to 16 messages can be contained in a single FIFO buffer. Each FIFO
buffer is used with a link to a transmit buffer. Only the message to be transmitted next in a FIFO buffer becomes
the target of transmit priority determination. Messages are transmitted sequentially on a first-in, first-out basis.
Figure 18-7 shows the allocation of transmit/receive FIFO buffer link.
Figure 18-7. Allocation of Transmit/Receive FIFO Buffer Links
18.6.1 Transmit Priority Determination
If transmit requests are issued from multiple buffers in the same channel, transmit priority is determined.
The priority is determined by using one of the following methods.
• ID priority (TPRI bit = 0)
• Transmit buffer number priority (TPRI bit = 1)
The setting of the TPRI bit in the GCFGL register is enabled in all CAN channels.
When the TPRI bit is set to 0, messages are transmitted according to the priority of stored message IDs. Priority of IDs
conforms to the CAN bus arbitration specification defined in the CAN specifications. IDs of messages stored in transmit
buffers and transmit/receive FIFO buffers (set to transmit mode) are targets of priority determination. When
transmit/receive FIFO buffers are used, the oldest message in a FIFO buffer becomes the target of priority determination.
When a message is being transmitted from a transmit/receive FIFO buffer, the next message in the FIFO buffer becomes
the target of priority determination.
When the TPRI bit is set to 1, the message in the transmit buffer of the minimum number among buffers with a transmit
request is transmitted first. When transmit/receive FIFO buffers are linked to transmit buffers, transmit priority is
determined according to linked transmit buffer numbers.
When messages are retransmitted due to an arbitration lost or an error, transmit priority determination is made again
regardless of the TPRI bit setting.
Only transmit buffers are used
Transmit/receive FIFO buffer 0
Transmit buffer 2
Transmit buffer 0
Transmit buffer 1
Transmit buffer 2
Transmit buffer 3
Transmit buffers and a transmit
receive FIFO buffer are used
(The transmit/receive FIFO
buffer is linked to transmit
buffer 1)
Transmit buffer 0
Transmit buffer 3
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