RL78/D1A User's Manual: Hardware - Renesas

Under development
Preliminary document
Specifications in this document are tentative and subject to change.
RL78/D1A CHAPTER 14 CAN CONTROLLER
14.9.5 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.
Suppose, for example, the same message buffer type is set to 5 message buffers, message buffers 10 to 14, and the
same ID is set to each message buffer. If the first message whose ID matches the 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 subsequent messages are received.
If 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
14. 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 IE bit of the C0MCTRLm register 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 not be stored in the message buffer having 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. The priority between MBRBs is mentioned in 14.9.1 Message Reception.
Remark m = 0 to 15
R01UH0317EJ0004 Rev. 0.04 891
Feb. 22, 2013