Datasheet

Section 15 Controller Area Network for Tiny (TinyCAN)
Rev. 4.00 Mar. 15, 2006 Page 328 of 556
REJ09B0026-0400
Internal Arbitration at Transmission: The TinyCAN transmits untransmitted messages in the
priority order from Mailbox 3 to Mailbox 1. The internal arbitration function selects the Mailbox
with the highest priority among all transmission request messages. Internal arbitration is based on
the three sources given below.
• TXPR/TXCR is set
• Arbitration lost during message transmission
• CAN bus error
TXPR/TXCR Setting: Figure 15.7 shows the timing of the TinyCAN internal arbitration caused
by the TXPR/TXCR setting. Transmit procedure and operation are as follows.
1. Write data of a transmit message to MCn0, MCn4 to MCn7, and MDn0 to MDn7 [n = 1 to 3]
before clearing the MBn bit in MBCR corresponding to the Mailbox of the transmit message to
0 (initial setting).
2. Set the corresponding MBn bit in TXPR to 1 (start condition issuance). Then, the start
condition is generated.
3. The internal arbitration for message 1 is determined and the transmit message is transferred to
the temporary buffer. After that, even if a transmit request cancellation is issued to the message
being transmitted by the DART or MBn bit in TXCR, message 1 is transmitted continuously
unless the TinyCAN detects an arbitration loss or error on the CAN bus.
4. After the seventh bit of the EOF has been transmitted (normal message transmission end), the
MBn bits in TXPR and TXCR which are corresponding Mailbox are cleared to 0 and the MBn
bit in TXACK and the EMPI bit in TCIRR1 are set to 1. At this time, the MBn bit in ABACK
is always 0. Then, message transmission is completed.
5. When there is a transmit request other than for message 1, the transmit message is transferred
to the temporary buffer and transmitted to the CAN bus after the arbitration for message 2 has
been determined. When there is no transmit request other than for message 1, the TinyCAN
performs reception.