Datasheet

V850ES/JG3-H, V850ES/JH3-H CHAPTER 20 CAN CONTROLLER
R01UH0042EJ0500 Rev.5.00 Page 991 of 1513
Aug 12, 2011
After the transmit message search, the transmit message with the highest priority of the transmit message 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 transmission request has a higher priority, it
is transmitted, unless transmission of a message with a low priority has already started. To solve this reversal of priorities,
software can request that transmission of a message of low priority be stopped. The highest priority is determined
according to the following rules.
Priority Conditions Description
1 (high)
Value of first 11 bits of ID
[ID28 to ID18]:
The message frame with the lowest value represented by the first 11 bits of the ID
is transmitted first. If the value of an 11-bit standard ID is equal to or smaller than
the first 11 bits of a 29-bit extended ID, the 11-bit standard ID has a higher priority
than a message frame with a 29-bit extended ID.
2 Frame type
A data frame with an 11-bit standard ID (C0MCONFm.RTR bit is cleared to 0) has
a higher priority than a remote frame with a standard ID and a message frame
with an extended ID.
3 ID type
A message frame with a standard ID (C0MIDHm.IDE bit is cleared to 0) has a
higher priority than a message frame with an extended ID.
4
Value of lower 18 bits of ID
[ID17 to ID0]:
If one or more transmission-pending extended ID message frame has equal
values in the first 11 bits of the ID and the same frame type (equal RTR bit
values), the message frame with the lowest value in the lower 18 bits of its
extended ID is transmitted first.
5 (low) Message buffer number
If two or more message buffers request transmission of message frames with the
same ID, the message from the message buffer with the lowest message buffer
number is transmitted first.
Remarks 1. If the automatic block transmission request bit C0GMABT.ABTTRG bit is set to 1 in the normal operation
mode with ABT, the TRQ bit is set to 1 only for one message buffer in the ABT message buffer group.
If the ABT mode was triggered by the ABTTRG bit (1), one TRQ bit is set to 1 in the ABT area (buffers 0
to 7). In addition to this TRQ bit, the application can request transmissions (set TRQ bit to 1) for other TX-
message buffers that do not belong to the ABT area. In that case an internal arbitration process (TX-
search) evaluates all of the TX-message buffers with the TRQ bit set to 1 and chooses the message
buffer that contains the highest prioritized identifier for the next transmission. If there are 2 or more
identifiers that have the highest priority (i.e. identical identifiers), the message located at the lowest
message buffer number is transmitted first.
Upon successful transmission of a message frame, the following operations are performed.
- The TRQ bit of the corresponding transmit message buffer is automatically cleared to 0.
- The transmission completion status bit CINTS0 of the C0INTS register is set to 1 (if the interrupt
enable bit (IE) of the corresponding transmit message buffer is set to 1).
- An interrupt request signal INTC0TRX is output (if the C0IE.CIE0 bit is set to 1 and if the interrupt
enable bit (IE) of the corresponding transmit message buffer is set to 1).
2. Before changing the contents of the transmit message buffer, the RDY flag of this buffer must be cleared.
Since the RDY flag may be temporarily locked while the internal processing is changed, it is necessary to
check the status of the RDY flag by software after changing the buffer contents.
3. m = 00 to 31