CAN Bus and J1939 Decoder

This tool supports CAN and SAE J1939 protocol analysis, covering ID decoding, signal extraction, log parsing, DBC decoding, and TP reassembly.

J1939 Overview

SAE J1939 is built on 29-bit extended CAN identifiers and is widely used in heavy-duty vehicles for real-time communication and diagnostics.

J1939 Identifier Structure

The 29-bit identifier contains Priority, EDP, DP, PF, PS, and SA fields. PF decides PDU1/PDU2 behavior and affects PGN/address interpretation.

PGN (Parameter Group Number)

PGN identifies message semantics and data purpose, serving as a core routing and meaning field in J1939.

When PF < 240, the frame is PDU1 and PS is destination address; when PF >= 240, the frame is PDU2 and PS becomes part of PGN.

Signal Extraction

One 8-byte CAN frame can contain multiple signals, each defined by start bit, length, byte order, and value type.

Physical value formula: Physical = Raw × Factor + Offset.

Common J1939 PGNs

• PGN 65262 (0xFEEE): Engine Temperature 1
• PGN 61444 (0xF004): Electronic Engine Controller 1
• PGN 65265 (0xFEF1): Cruise Control / Vehicle Speed
• PGN 65269 (0xFEF5): Ambient Conditions
• PGN 65263 (0xFEEF): Engine Fluid Level / Pressure

Use Cases

• ECU development and integration validation
• Vehicle diagnostics and communication troubleshooting
• Fleet telemetry for fuel and maintenance analytics
• Powertrain calibration and test verification
• Protocol learning with real CAN/J1939 frames

Byte Order

Intel (little-endian) and Motorola (big-endian) follow different bit ordering rules. Correct selection is critical for accurate decoding.

Feature Overview

• ID decode for 29-bit J1939 and 11-bit standard CAN
• Bit-level extraction with signed/unsigned/float support
• Log parser for candump/ASC/TRC and CSV export
• DBC message/signal/node browsing and quick decode

DBC Support

DBC files define messages, signals, nodes, comments, attributes, and value maps. This tool supports common Vector CANdb++ syntax.

After loading, you can search messages/signals, inspect node transmit relations, and decode raw CAN payload with predefined signal definitions.

Supported Input Formats

• Hex with spaces: FF 00 11 22 33 44 55 66
• Hex compact: FF00112233445566
• Base64: /wARIjNEVWY=
• C/C++ array: 0xFF, 0x00, 0x11, 0x22, ...

Log Formats

• candump: (1234567890.123456) can0 18FEF100#FF00112233445566
• Vector ASC: 0.000000 1 18FEF100x Rx d 8 FF 00 11 22 33 44 55 66
• PCAN TRC: 1) 1234.5 18FEF100 8 FF 00 11 22 33 44 55 66