LIN Protocols
This section documents the LIN (Local Interconnect Network) protocol specifications for various devices commonly found in motorhomes and RVs.
LIN Protocol Overview
LIN (Local Interconnect Network) is a serial network protocol used for communication between electronic components in vehicles and other applications. It provides a cost-effective solution for connecting devices that don’t require the full complexity of CAN bus.
Technical Specifications
- Baud Rate: 19,200 bps (standard for most automotive applications)
- Bus Architecture: Single-wire plus ground
- Topology: Master-slave with up to 16 slave nodes
- Frame Format: Header (master) + Response (slave)
- Data Length: 2, 4, or 8 bytes per frame
LIN Diagnostic Frames
LIN protocol includes standardized diagnostic frames for device discovery and identification. These frames are used by CI devices for automatic device detection.
Frame IDs
- 0x3C: Master Request Frame (diagnostic requests from master to slaves)
- 0x3D: Slave Response Frame (diagnostic responses from slaves to master)
Both frames always contain 8 data bytes.
Read By Identifier (SID 0xB2)
The most common diagnostic service for device discovery. The master sends a request to read product identification from slave nodes.
Request Frame (0x3C):
| Byte | Field | Description |
|---|---|---|
| 0 | NAD | Node Address - target device address |
| 1 | PCI | Protocol Control Information (0x06 for single frame, 6 data bytes) |
| 2 | SID | Service Identifier (0xB2 = Read By Identifier) |
| 3 | Identifier | 0x00 = Product Info, 0x01 = Serial Number, 0x20-0x3F = User defined |
| 4 | Data 1 | Supplier ID LSB (little-endian) |
| 5 | Data 2 | Supplier ID MSB |
| 6 | Data 3 | Function ID LSB (little-endian) |
| 7 | Data 4 | Function ID MSB |
Response Frame (0x3D) for Product Info (Identifier 0x00):
| Byte | Field | Description |
|---|---|---|
| 0 | NAD | Node Address - responding device |
| 1 | PCI | 0x06 (single frame, 6 data bytes) |
| 2 | RSID | Response SID (0xF2 = positive response to 0xB2) |
| 3 | Data 1 | Supplier ID LSB |
| 4 | Data 2 | Supplier ID MSB |
| 5 | Data 3 | Function ID LSB |
| 6 | Data 4 | Function ID MSB |
| 7 | Data 5 | Variant ID |
LIN Product Identification Fields:
- Supplier ID (16-bit): Assigned by LIN Consortium to each manufacturer
- Function ID (16-bit): Device type identifier (assigned by supplier)
- Variant ID (8-bit): Product variant identifier
Known Supplier IDs
| Supplier ID | Manufacturer |
|---|---|
| 0x1234 | Dometic |
| 0x1987 | Votronic |
| 0x41DE | Alde |
| 0x4617 | Truma |
| 0x55BE | Büttner |
| 0x7468 | Thetford |
Positive Response: RSID = SID + 0x40 (e.g., 0xB2 + 0x40 = 0xF2)
Checksum: Diagnostic frames (0x3C-0x3F) use classic checksum (sum of data bytes only, PID excluded).
Protocol References
- LIN Standards ↗ - Official LIN consortium specifications
- ISO 17987 Standards ↗ - International standard for LIN communication