EP80579 Datasheet, PDF (1577/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
Note:
39.4.3.4
Note:
39.4.4
39.4.4.1
When a transmitting node has transmitted an error frame to completion or has received
one, it immediately attempts to transmit the previously transmitted message again
with another bus arbitration process.
The error signaling mechanism ensures that the message transfer with all nodes of a
network is error-free and consistent. Because error signaling takes place immediately
after an error is detected, short error recovery times are guaranteed.
The CAN protocol also provides a self-monitoring mechanism that prevents one
dysfunctional node from holding the network down. The assessment of a node’s
statistical error rate may result in deactivation of the node.
Overload Frames
An Overload Frame has the same format as an active Error Frame. The difference is
when the Overload Frame is transmitted and its purpose: An Overload Frame is only
permitted to transmit during Interframe Space (Intermission). Two conditions lead to
the generation of an Overload Frame:
• If a node is not yet ready for any data (insert wait state).
• A node detects a dominant bit during intermission. A node may generate at most 2
consecutive Overload Frames, to delay the next Data or Remote Frame.
Overload Frames consist of two fields:
• The Overload Flag has the same format as an active Error Frame.
• The Overload Delimiter consists of eight recessive bits.
The CAN controller will not generate overload frames. However, it will respond to
overload frames when it sees one on the bus.
CAN Bit Timing
Introduction
The CAN network is configured based on the bit rate. The nominal bit rate is the
number of bits per second passing through the network in the absence of re
synchronization. Each member of this network can implement the required timing
parameters for a given bit rate using different values as long as the chosen values meet
the synchronization requirements.
Oscillator drift and other issues could make the nominal configured bit rate to vary but
the CAN protocol provides a mechanism to re synchronize the messages.
The nominal bit rate is made up of the following non-overlapping segments:
• Synchronization Segment: This is the start of the frame segment of the bit being
transmitted. It is used primarily to synchronize nodes on the bus. The
synchronization segment is always fixed to 1 time quanta.
• Propagation Segment: The is the time required for signals to travel in the CAN
network. It includes the time required to travel from one end of the system to the
other and back again. It also accounts for the CAN components to react.
• Phase Buffer Segment 1 & 2: These phase buffers exists to compensate for timing
problems created by the oscillator drift and other issues. These 2 segments are
adjusted in units called the Synchronization Jump Width.
• Sample Point: The sample point always occurs between the Phase 1 and Phase 2
segments. It can be set to be either single or multiple.
August 2009
Order Number: 320066-003US
Intel^® EP80579 Integrated Processor Product Line Datasheet
1577