Datasheet

V850ES/JG3-H, V850ES/JH3-H CHAPTER 20 CAN CONTROLLER
R01UH0042EJ0500 Rev.5.00 Page 988 of 1513
Aug 12, 2011
20.9.5 Multi buffer receive block function
The multi buffer receive block (MBRB) function is used to store a block of data in two or more message buffers
sequentially with no CPU interaction, by setting the same ID to two or more message buffers with the same message
buffer type. These message buffers can be allocated in any area in the message buffer memory, and they are not
necessarily to be allocated adjacent to each other.
Suppose, for example, the same message buffer type is set to 10 message buffers, message buffers 10 to 19, and the
same ID is set to each message buffer. If the first message whose ID matches an ID of the message buffers is received, it
is stored in message buffer 10. At this point, the DN bit of message buffer 10 is set, prohibiting overwriting the message
buffer.
When the next message with a matching ID is received, it is received and stored in message buffer 11. Each time a
message with a matching ID is received, it is sequentially (in the ascending order) stored in message buffers 12, 13, and
so on. Even when a data block consisting of multiple messages is received, the messages can be stored and received
without overwriting the previously received matching-ID data.
Whether a data block has been received and stored can be checked by setting the C0MCTRLm.IE bit of each message
buffer. For example, if a data block consists of k messages, k message buffers are initialized for reception of the data
block. The IE bit in message buffers 0 to (k-2) is cleared to 0 (interrupts disabled), and the IE bit in message buffer k-1 is
set to 1 (interrupts enabled). In this case, a reception completion interrupt occurs when a message has been received and
stored in message buffer k-1, indicating that MBRB has become full. Alternatively, by clearing the IE bit of message
buffers 0 to (k-3) and setting the IE bit of message buffer k-2, a warning that MBRB is about to overflow can be issued.
The basic conditions of storing receive data in each message buffer for the MBRB are the same as the conditions of
storing data in a single message buffer.
Cautions 1. MBRB can be configured for each of the same message buffer types. Therefore, even if a
message buffer of another MBRB whose ID matches but whose message buffer type is different
has a vacancy, the received message is not stored in that message buffer, but instead discarded.
2. MBRB does not have a ring buffer structure. Therefore, after a message is stored in the message
buffer having the highest number in the MBRB configuration, a newly received message will no
longer be stored in the message buffer in the order from the lowest message buffer number.
3. MBRB operates based on the reception and storage conditions; there are no settings dedicated to
MBRB, such as function enable bits. By setting the same message buffer type and ID to two or
more message buffers, MBRB is automatically configured.
4. With MBRB, “matching ID” means “matching ID after mask”. Even if the ID set to each message
buffer is not the same, if the ID that is masked by the mask register matches, it is considered a
matching ID and the buffer that has this ID is treated as the storage destination of a message.
5. Priority among each MBRB conforms to the priority shown in 20.9.1 Message reception.
Remark m = 00 to 31