Network Communications System Description (With SH-AWD) (2015-17)

CAN (Controller Area Network) and the LIN (Local Interconnect Network) 

The vehicle uses CAN (Controller Area Network) and LIN (Local Interconnect Network) as the in-vehicle LAN (Local Area Network). These networks enable the control units to exchange the information over the CAN bus.

The CAN consists of the F-CAN network that enables the control units to exchange the signals regarding the power train/chassis and the B-CAN network for the signals regarding the body. These networks are inter-connected at the gauge control module (gateway).

The LIN is a network for connecting the gauge control module and the 12 volt battery sensor; as well as for connecting the power window master switch, front passenger's power window switch, left rear power window switch, right rear power window switch, and the moonroof control unit/motor, ensuring a reliable communication suitable for the control system.

As multi-communication system occur between several control units, the system also provides the K-LINE and the L-LINE for transmitting the diagnostic results to the HDS (Honda Diagnostic System) and the S-NET for transmitting the immobilizer signals.

Without CAN Gateway 

Courtesy of HONDA, U.S.A., INC.

With CAN Gateway 

Courtesy of HONDA, U.S.A., INC.

CAN 

The CAN (control area network) is a multi communication system that ISO has developed and standardized for the automobile.

The CAN employs a multi-master system in which multiple control units connected to a bus communicate with each other.

Communicating Method 

CAN communication uses a data frame format on the CAN line. The CAN uses the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) method to data frame collisions. This method transmits information only when the bus is sensed to be idle. The data frame uses "0" (dominant) and "1" (recessive) to create a message, which consists of the data field (message), arbitration field (data ID), control field (data length), CRC field (sending error detection), and the ACK field (end of message). After sending the data, each control unit classifies the data by the controller ID and controls outputs as commanded.

Courtesy of HONDA, U.S.A., INC.

F-CAN 

The network connecting the powertrain and chassis is called F-CAN and it employs high speed CAN with communication rate at 500 kbps.

The F-CAN is composed of a single F-CAN Bus. To respond to the increase in the number of ECUs connected to the F-CAN and the increase in the amount of communication, the composition of the F-CAN network is divided into multiple bus lines, and an F-CAN gateway with a data-forwarding function is established, enabling the communication among the CAN Bus lines.

Connection of each control unit has control units with terminating resistor installed for preventing signal from being reflected back at each end of a pair of twisted signal cable which is comprised of F-CAN_H and F-CAN_L, with other control units in parallel connection between them.

By rapidly switching between equal and unequal voltages, digital data can be transmitted in bits.

B-CAN 

The network between control units for body electrical system is called B-CAN and it employs low speed CAN with communication rate at 125 kbps.

Connection of each control unit has control units with terminating resistor installed for preventing signal from being reflected back at each end of a pair of twisted wire which is comprised of B-CAN_H and B-CAN_L, with other control units in parallel connection between them.

Power Saving Mode Control 

Since some control units for the body system are functional even if turning the vehicle is in the OFF (LOCK) mode, the power-saving mode is set for these units for the purpose of reducing the dark current.

Transition to the power-saving mode (sleep mode) and returning from it (wakeup mode) are controlled by the active, sleep and wakeup signals. The control units that are not in "wait for sleep" state send periodically the active signals to the bus line and stop sending them when it is in "wait for sleep" state.

When all control units do not send the active signal anymore, one or more control units send the sleep signals. The control units that received the sleep signals go into the power-saving mode.

In the event of inputs from switch or sensor during the power-saving mode, they send the wakeup signals to the bus line. In this case, they return from the power-saving mode.

LIN 

Overview 

The LIN is a bus based on UART (Universal Asynchronous Receiver/Transmitter). Communication rate of LIN is slower than that of CAN, and it is used for systems for which a high speed communication is not required. It is able to reduce the wire harness bulk as well as to reduce cost due to its connection with each control unit with just single bus. The LIN employs a single-master system, in which one ECU serves as a master control unit to control all the signals on the LIN bus. Other units become slave units to serve in accordance with request from the master control unit. This vehicle employs a LIN with a communication speed of 19.2 kbps for connecting the gauge control module and the 12 volt battery sensor; and a LIN with a communication speed of 9.6 kbps for connecting the power window master switch, front passenger's window switch, left rear power window switch, right rear power window switch, and the moonroof control unit/motor.

Communication System 

LIN uses a single-master system, where one ECU controls all bus communication.

The other controllers act as slave units, communicating only when requested by the PCM.

The message frame is comprised of the header frame that sends the master's request and the response frame that sends the slave's response. The header frame consists of the SYNCH BREAK field for showing the frame start, SYNCH field for correcting the baud rate, and the IDENT field for showing the control unit that requests the response. The response frame consists of the data fields and the CHECK SUM field for detecting transmitting errors.

Courtesy of HONDA, U.S.A., INC.

Power Saving Mode 

The body electrical system has a control unit which does not stop operating when the vehicle to the OFF (LOCK) mode in order to perform door lock control and light control. These control units have a power saving mode to reduce the standby power requirement.

Network Communication Troubleshooting 

The HDS (Honda Diagnostic System) uses the K-LINE for displaying the control unit and self-diagnostic results both in F-CAN bus and B-CAN bus. The K-LINE bus is the communication circuit that uses the UART whose baud rate is 10.4 kbps. The combination meter provides the display function for body-system DTC (Diagnostic Trouble Code). The DTCs are displayed when the gauge control module receives the SCS terminal short signal via the F-CAN bus or the MICU service check ON signal via the B-CAN bus. Then, the gauge control module reads the self-diagnostic results sent by each control unit via B-CAN bus, and displays the DTCs.

Vehicles equipped with keyless access, also have an L-LINE data bus that connects the DLC to the keyless access/TPMS control unit.

This line allows the HDS to communicate with the keyless access/TPMS control unit if the remote is lost or malfunctioning, preventing the ignition from being switched on. The S-NET serves as a path to transmit a signal from a transponder integrated into the remote, to control units related to the immobilizer system, such as the PCM and the MICU.

Without CAN Gateway 

Courtesy of HONDA, U.S.A., INC.

With CAN Gateway 

Courtesy of HONDA, U.S.A., INC.