LIN basics — ISO 17987, LDF, and conformance testing

A LIN network has one master and several slaves. There is no arbitration as in CAN: the master sends a header and the addressed slave returns the response.

In other words, who speaks when is completely determined by the master's schedule table. That is good for determinism, but it also means a slave cannot spontaneously send an urgent notification.

The bit rate is around 20 kbit/s at most — far slower than CAN. Always check from the number of signals and their update periods that this bandwidth is enough.

The LDF (LIN Description File) describes the nodes, frames, signals, and schedule tables on a bus in one file.

In LIN the LDF is effectively the blueprint. Many drivers generate their configuration code from the LDF, which keeps things more consistent than hand-written code.

The standard also defines building the LDF from NCFs (Node Capability Files) that describe each slave's capabilities.

After LIN 1.3 / 2.0 / 2.1 / 2.2A, the protocol is now the international standard ISO 17987. Diagnostic and configuration services differ between versions, so check that you match the devices you connect to.

SAE J2602 is a North American specification based on LIN 2.x, with its own requirements for bit rate and fault behavior. OEM-specific options (such as GMW) may be added.

When several identical slaves share a bus (seat motors, for example), you need to tell which one is in which position.

SNPD (Slave Node Position Detection) assigns addresses to slaves automatically after power-up. Positions are identified without relying on wiring or per-unit settings, which cuts cost in both production and service.

There are several methods, and support depends on the parts used (LIN transceivers or power ICs).

UDS-based diagnostics are also used on LIN. Because the bandwidth is narrow, reading data as you would on CAN takes unexpectedly long.

Firmware updates over LIN are possible, but estimate from the image size first whether the transfer time is practical. If not, design an update route from the CAN side.

LIN conformance tests cover both the data-link layer (DLL) and the physical layer: bit timing, sleep/wake-up behavior, error handling, and electrical characteristics (rise times, thresholds, load conditions).

Physical-layer faults may not appear in bench bus tests and show up only under real-vehicle temperature and load. If the OEM requires test reports from an accredited lab, checking the test items early in development reduces rework.