LIN Bus Timing Calculator
Calculate LIN bus bit time, break field length, frame time, and maximum frame rate for automotive LIN network design.
Formula
Reference: LIN Specification Package Revision 2.2A
How It Works
This calculator determines LIN bus frame timing parameters for automotive body electronics. Automotive engineers and ECU designers use it to configure master-slave scheduling per LIN 2.2A specification (ISO 17987). LIN is a single-wire, single-master protocol operating at 1-20 kbps, designed for cost-sensitive applications where CAN's complexity is unnecessary. LIN protocol timing is standardized in ISO 17987-1 through ISO 17987-7 (Road vehicles — Local Interconnect Network), which supersede the LIN Consortium's LIN 2.2A specification document published in 2010. Each frame consists of: break field (>=13 bits low), break delimiter (1 bit high), sync byte (0x55 pattern), protected identifier (6-bit ID + 2-bit parity), 1-8 data bytes, and enhanced checksum. At 19.2 kbps (the most common rate), bit time is 52.08 microseconds. The frame slot time for an 8-byte message is calculated as: T_frame = T_header + T_response = (34 + 10n) x T_bit = (34 + 80) x 52.08 us = 5.94 ms. LIN master scheduling must allocate frame slots with 40% timing margin per LIN 2.2A Section 2.4.2 to accommodate slave response jitter.
Worked Example
A car door module communicates with 4 LIN slaves (mirror, window, lock, lighting) at 19.2 kbps with varying data lengths. Per LIN 2.2A specification Section 2.4: Bit time = 1/19200 = 52.08 us. Mirror status (2 bytes): T_header_nominal = 34 bits x 52.08 us = 1.77 ms. T_response_nominal = (10 x 2 + 10) bits x 52.08 us = 1.56 ms. T_frame_nominal = 3.33 ms. With 40% margin: T_slot = 3.33 x 1.4 = 4.66 ms. Window position (4 bytes): T_frame = (34 + 50) x 52.08 us = 4.37 ms, T_slot = 6.12 ms. Total schedule cycle: 4.66 + 6.12 + 4.66 + 6.12 = 21.56 ms, achieving 46 Hz update rate for all slaves.
Practical Tips
- ✓Per LIN 2.2A Section 2.3.1.1, master break field must be >=13 bits (676 us at 19.2 kbps) - use 14-15 bits for margin against slave detection jitter
- ✓Schedule event-triggered frames (multiple slaves respond to same ID) with collision resolution time of 2x normal slot to handle simultaneous responses
- ✓For diagnostic frames (ID 0x3C/0x3D), allocate 8-byte response slot even if typical data is shorter - diagnostics always use 8-byte PDUs
Common Mistakes
- ✗Setting bit rate to exactly 19200 Hz - LIN specification requires +/-14% tolerance (16512-21888 Hz), but slaves at edge cases may fail sync
- ✗Allocating frame slots without 40% margin, causing schedule overrun when slaves respond at maximum allowed delay (8 bit times per byte)
- ✗Using classic checksum (sum of data bytes only) instead of enhanced checksum (includes PID) for LIN 2.x slaves, causing 100% checksum failures
Frequently Asked Questions
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