NEC V850ES/F 3-L Series User Manual page 611

CAN Controller (CAN)
Priority Conditions
1 (high) Value of first 11 bits of ID
[ID28 to ID18]:
2 Frame type
3 ID type
4 Value of lower 18 bits of ID
[ID17 to ID0]:
5 (low) Message buffer number
Note
Description
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.
A data frame with an 11-bit standard ID (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.
A message frame with a standard ID (IDE bit is cleared to 0) has a
higher priority than a message frame with an extended ID.
If two 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.
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.
1. If the automatic block transmission request bit ABTTRG 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 ABTTRG bit (1), one TRQ bit is set to 1
in the ABT area (buffer 0 through 7). Beyond 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 interval arbitration
process (TX-search) evaluates all TX-message buffers with 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 at first.
Upon successful transmission of a message frame, the following
operations are performed.
• The TRQ flag of the corresponding transmit message buffer is
automatically cleared to 0.
• The transmission completion status bit CINTS0 of the CnINTS 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 INTCnTRX is output (if the CIE0 bit of the
CnIE register is set to 1 and if the interrupt enable bit (IE) of the
corresponding transmit message buffer is set to 1).
2. When changing the contents of a transmit buffer, the RDY flag of this buffer
must be cleared before updating the buffer contents. As during internal
transfer actions, the RDY flag may be locked temporarily, the status of RDY
must be checked by software, after changing it.
User's Manual U18743EE1V2UM00
Chapter 18
611