R01UH0823EJ0100 Rev.1.00
Page 1271 of 1823
Jul 31, 2019
RX23W Group
36. CAN Module (RSCAN)
36.5
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.
shows the allocation of transmit/receive FIFO buffer link.
Figure 36.7
Allocation of Transmit/Receive FIFO Buffer Links
36.5.1
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 (GCFGL.TPRI bit = 0)
Transmit buffer number priority (GCFGL.TPRI bit = 1)
The setting of the GCFGL.TPRI bit is enabled in all CAN channels.
When the GCFGL.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 ISO 11898-1 standard. 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 GCFGL.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 GCFGL.TPRI bit setting.
Transmit buffer 0
Transmit buffer 1
Transmit buffer 2
Transmit buffer 3
Only transmit buffers are used
Transmit buffer 0
Transmit/receive FIFO buffer 0
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)