Message Overview

This implementation sends 6 messages every 20 ms (50 Hz cycle). All use 29-bit extended IDs and 8 data bytes, conforming to SAE J1939.

Message table

29-bit ID structure

Every J1939 message ID encodes three fields:

Byte convention

Unused bytes are always set to 0xFF, which in J1939 means parameter not available (SNA — Specific Not Available).

Byte:   0     1     2     3     4     5     6     7
      ┌─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┐
      │ FF  │ FF  │ FF  │ Lo  │ Hi  │ FF  │ FF  │ FF  │
      └─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┘
                          ↑     ↑
                    Actual data (little-endian)

Send cycle

All 6 messages are sent sequentially every 20 ms:

void loop() {
    // send all messages
    // ...
    delay(20);  // 50 Hz
}

Source addresses in use