SYSTEM OPERATION
- Each ECU communicating with CAN periodically sends several sensors’ information on CAN bus as data frame (called periodical sending data). For further details, consult the data frame section.
- ECUs requiring data on CAN bus can receive data frames sent from each ECU simultaneously.
- The data sent from each ECU conducting CAN communication is transmitted at 10-1000 msec intervals depending on necessity of data.
note In the figure above, the data frame A is transmitted in "a" intervals, while the data frames B and C are transmitted at intervals "b" and "c," respectively. - A single ECU transmits multiple data frames.
- When data frames conflict with one another (when plural ECUs transmit signals simultaneously), data is prioritised for transmission by mediation, therefore, plural data frames are not sent simultaneously. For further details, consult the mediation section.
- Data is transmitted not by the conventional voltage-using method but by voltage potential difference. For further details, consult the section on CAN bus voltage transformation
.
- Reliability of each ECU transmitting signals via CAN communication is secured by several error detection and recovery processes. For further details, consult the sections on error detection and system recovery.
- For major communication signals (transmitting signals) among ECUs.
MEDIATION
- Data frame with high priority is transmitted first according to ID codes memorized in data frames.
- Transmission of low-priority data (data frames) is suspended by the issuing ECUs until the bus clears (when no transmission data exists on the CAN bus).
note If the suspended state continues for a specific time, new data (data frame content) is created and sent. - ECU containing suspended data frames transmits the data when the bus becomes available.
note | There is enough capacity on the CAN bus, which never prevents data frames from being sent. |
VOLTAGE TRANSFORMATION ON THE CAN-B BUS and CAN-C BUS
DATA FRAMES
SOF (Start of Frame)
- Indicates the start of the frame
- Identifies the data content while specifying priority rank in case of mediation
- Specifies the frame type, data length, etc.
- Values used for data control, etc.
- Region where to check for errors in sent data. The transmitting ECU calculates data regions by applying prescribed operations and stores the results. The receiving ECU detects erroneous communication by comparing the CRC region with the data region.
- Region where to conform the reception of sent data
- Indicates the end of the frame