Introduction #

The Local Interconnect Network (LIN Bus) is a low-cost, single-wire serial communication protocol designed as a complement to CAN Bus. Introduced in the late 1990s by a consortium of automotive manufacturers, LIN was created to reduce costs and complexity for applications that do not require the full performance of CAN.

Unlike CAN, which is multi-master and message-based, LIN is a master-slave, deterministic network. This makes it ideal for simpler, body-control related functions such as window lifters, mirror adjustment, seat control, wipers, and climate control, where communication speed and bandwidth requirements are lower.

Some key characteristics of LIN Bus include:

• Low cost – Uses a single-wire physical layer and inexpensive transceivers.
• Deterministic scheduling – Communication is based on a predefined schedule set by the master, eliminating arbitration.
• Scalability – Typically supports up to 16 nodes per cluster, suitable for localized subsystems.
• Integration with CAN – LIN clusters often connect to a vehicle’s main CAN backbone via a gateway ECU.
• Simplicity – Message handling and timing are predictable and easier to implement compared to CAN.

Because of these qualities, LIN Bus is now a standard solution for cost-sensitive automotive subsystems, especially in body electronics. It complements CAN by offloading simple tasks while ensuring compatibility within the overall vehicle network architecture.

Protocols #

While the LIN standard (ISO 17987) defines how data is transmitted, higher-level rules specify message scheduling, diagnostics, and node behavior. Two aspects relevant for LIN-based systems are:

LIN Cluster / Scheduling #

LIN operates with a single master node that controls communication by sending header frames at scheduled intervals. Slave nodes respond only when addressed by the master. In practice:

• Fixed schedule – Communication follows a predefined frame schedule, ensuring deterministic timing.
• Frame identifiers – Each message slot is identified by an ID (6 bits + parity), determining which slave may respond.
• Signal encoding – Frames contain signals such as switch states, actuator commands, or sensor values.
• Synchronization – Slave nodes synchronize their internal clocks using the master’s sync field.

This makes LIN highly predictable and efficient for cyclic, low-bandwidth tasks.

Diagnostic Protocol (UDS on LIN, ISO 14229 / ISO 17987) #

LIN supports diagnostics through a standardized mechanism defined in ISO 17987, often leveraging UDS (ISO 14229) for consistency with CAN-based diagnostics.

Key aspects include:

• Master–slave diagnostics – The master typically acts as a diagnostic gateway, forwarding tester requests to LIN slaves.
• UDS services – Reading DTCs, monitoring signals, and updating slave software via LIN.
• Single-frame and multi-frame transport – Diagnostic messages can be short (single frame) or segmented for larger data.
• Standardization – Ensures LIN slaves can be diagnosed and updated using the same service framework as CAN.

Together, LIN’s cluster scheduling and diagnostic extensions make it a reliable, cost-effective solution for non-critical automotive subsystems, while ensuring integration with industry-standard diagnostic tools and processes.