Network Communications System Description

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

The vehicle uses the CAN (Controller Area Network) and the 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 powertrain/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 PCM, the alternator, and the 12 volt battery sensor, ensuring reliable communication suitable for the control system.

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

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.

F-CAN

The network connecting the powertrain and chassis is called F-CAN and it employs high speed CAN with a communication rate of 500 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 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 a communication rate of 125 kbps.
Connection of each control unit has control units with terminating resistor installed for preventing a 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 to 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 periodically send 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. 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 thanks to its connection with each control unit with just single bus. The LIN employs a single-master system, in which only single master control unit 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 PCM, the alternator, and the 12 volt battery sensor.

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.

Power Saving Mode

The body electrical system has a control unit which does not stop operating when turning 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 (Universal Asynchronous Receiver Transmitter) whose baud rate is 10.4 kbps. The combination meter provides the display function for body-system DTC (Diagnostic Trouble Code). The DTC is 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 DTC.
Vehicles equipped with keyless access, also have an L-LINE data bus that connects the DLC to the keyless access control unit.
This line allows the HDS to communicate with the keyless access control unit if the keyless remotes are 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 MICU.