Datasheet

Section 15 Controller Area Network for Tiny (TinyCAN)
Rev. 4.00 Mar. 15, 2006 Page 329 of 556
REJ09B0026-0400
HRXD
Bus idle
Message 1 Message 2
Message 2Message 1
[4] Clear MBn in TXPR and MBn in TXCR
[4] Set MBn in TXACK and EMPI in TCIRR1
Transmission for message 2
cannot be cancelled by TXCR
Internal arbitration for message 3
can be configurable
[5] Internal arbitration for message 2
is determined
[3] Set MBn bit in TXCR immediately after internal arbitration
for message 1 has been determined
[2] Set TXPR
Transmission for message 1 cannot be cancelled by TXCR
Internal arbitration for message 2 can be configurable
(Transmission settings can be changed by TXPR/TXCR)
Bus idle
SOF Arbitration Control Data CRC ACK EOF
Intermission
SOF
SOF Arbitration Control Data CRC ACK EOF
Intermission
HTXD
MBn in TXPR
MBn in TXCR
MBn in TXACK
EMPI in TCIRR1
MBn in ABACK
Figure 15.7 Internal Arbitration at Transmission Caused by TXCR/TXPR Setting
Arbitration Lost during Message Transmission: If an arbitration loss on the CAN bus occurs,
the TinyCAN halts transmission, and starts message reception. If the DART bit for the
transmission-requested message is cleared to 0, on the completion of reception, the transmission-
requested message is retransmitted. However, if the DART bit is set to 1, it is not transmitted in
frame 2. Figures 15.8 to 15.10 show the timings of the arbitration loss on the CAN bus. 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.