EP80579 Datasheet, PDF (1572/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
39.4.3 Frame Types
The CAN protocol is defined and controlled by four different frame types:
• Data Frame - Data frame from a transmitting node to receiving nodes.
• Remote Frame - Receiving node requesting the data frame with equal identifier.
• Error Frame - Transmitted by any node that detected an error.
• Overload Frame - A node can generate an overload frame under two conditions:
— If the node detects a dominant bit during the interframe space (intermission).
— The node is not yet ready to receive another data frame (wait states). Nodes
are not allowed to generate more than 2 consecutive overload frames to delay
the next transfer.
— The CAN unit will not generate an overload frame but will respond to it if it sees
one on the bus.
39.4.3.1 Data Frame
A standard CAN data frame is composed of seven fields, as shown in Figure 39-2.
Figure 39-2. Standard CAN Data Frame
Standard Data Frame
Recessive level
Bus Idle _{1 11 1 1 1 4}
Dominant level
Start of Frame
Arbitration Field
Identifier
RTR Bit (D)
IDE Bit (D)
Control Field Reserved (D)
DLC
0...64
15 1 1 1 7
3 ^{Bus Idle}
Data Field
CRC Field
CRC Sequence
CRC Delimiter
Acknowledge Field
ACK Slot
ACK Delimiter
End of Frame
Intermission
• Start of Frame: One dominant bit marks the beginning of Data Frames and Remote
Frames. The purpose is hard synchronization for all nodes.
• Arbitration Field, consisting of:
— 11 bit identifier
— 1 RTR bit. This bit is used to distinguish between a Data Frame (Dominant) and
a Remote Frame (Recessive).
Intel^® EP80579 Integrated Processor Product Line Datasheet
1572
August 2009
Order Number: 320066-003US