SH7137 Datasheet, PDF (800/1160 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer SuperH™ RISC engine Family

Section 19 Controller Area Network (RCAN-ET)
• Internal Arbitration for transmission
The following diagram explains how RCAN-ET manages to schedule transmission-requested
messages in the correct order based on the CAN identifier. 'Internal arbitration' picks up the
highest priority message amongst transmit-requested messages.
CAN bus
state
RCAN-ET
scheduler state
Transmission
Frame-1
Reception
Frame-2
Transmission
Frame-3
Bus Idle SOF Message EOF Interm SOF Message EOF Interm SOF
Tx Arb for Tx/Rx Arb for
Frame-1 Frame-1
Tx Arb for
Frame-3
Tx/Rx Arb for
Frame-3/2
Tx Arb for
Frame-3
Tx/Rx Arb for
Frame-3
Scheduler
start point
TXPR/TXCR/
Error/Arb-Lost
1-1
1-2
2-1
2-2
3-1
3-2
Set Point
Interm:
SOF:
EOF:
Message:
Intermission Field
Start Of Frame
End Of Frame
Arbitration + Control + Data + CRC + Ack Field
Figure 19.11 Internal Arbitration for Transmission
The RCAN-ET has two state machines. One is for transmission, and the other is for reception.
1-1: When a TXPR bit(s) is set while the CAN bus is idle, the internal arbitration starts running
immediately and the transmission is started.
1-2: Operations for both transmission and reception starts at SOF. Since there is no reception
frame, RCAN-ET becomes transmitter.
2-1: At crc delimiter, internal arbitration to search next message transmitted starts.
2-2: Operations for both transmission and reception starts at SOF. Because of a reception frame
with higher priority, RCAN-ET becomes receiver. Therefore, Reception is carried out instead
of transmitting Frame-3.
3-1: At crc delimiter, internal arbitration to search next message transmitted starts.
3-2: Operations for both transmission and reception starts at SOF. Since a transmission frame has
higher priority than reception one, RCAN-ET becomes transmitter.
Internal arbitration for the next transmission is also performed at the beginning of each error
delimiter in case of an error is detected on the CAN Bus. It is also performed at the beginning of
error delimiters following overload frame.
Rev. 2.00 Sep. 10, 2008 Page 774 of 1130
REJ09B0402-0200