CAN Protocol Reference

The AddVantage PPG uses J1939 protocol over CAN bus at 250 kbit/s to receive engine data from the ECU.

Overview

J1939 is a higher-layer protocol built on CAN 2.0B (29-bit identifiers). The 29-bit arbitration ID contains:

Bits	Field	Description
28-26	Priority	0-7 (lower = higher priority)
25-24	Reserved	Usually 0
23-16	PGN (high)	Parameter Group Number
15-8	PGN (low)
7-0	Source Address	Transmitting ECU address

Extracting PGN from CAN ID

uint32_t extract_pgn(uint32_t can_id) {
    // Mask off priority and source address
    uint32_t pgn = (can_id >> 8) & 0x3FFFF;

    // For PDU1 format (PS < 240), PS is destination address
    if (((pgn >> 8) & 0xFF) < 240) {
        pgn &= 0x3FF00;  // Mask off PS field
    }
    return pgn;
}

Supported PGNs

EEC1 (61444) - Electronic Engine Controller 1

Primary engine parameters. Transmitted at 10-100ms intervals.

Byte	Parameter	Resolution	Range
0	Engine Torque Mode	4 bits	0-15
1	Driver Demand Torque	1%/bit - 125	-125 to 125%
2	Actual Engine Torque	1%/bit - 125	-125 to 125%
3-4	Engine Speed	0.125 RPM/bit	0-8031.875 RPM
5	Source Address	-	0-255
6-7	Starter Mode	-	-

Parsing Engine Speed (RPM):

uint16_t speed_raw = data[3] | (data[4] << 8);
uint16_t rpm = (uint16_t)(speed_raw * 0.125);

Parsing Torque (%):

int8_t torque = data[2] - 125;  // Range: -125% to +125%

ET1 (65262) - Engine Temperature 1

Engine temperature sensors. Transmitted at 1000ms intervals.

Byte	Parameter	Resolution	Range
0	Engine Coolant Temp	1°C/bit - 40	-40 to 210°C
1	Fuel Temp	1°C/bit - 40	-40 to 210°C
2-3	Engine Oil Temp	0.03125°C/bit - 273	-273 to 1735°C
4-5	Turbo Oil Temp	0.03125°C/bit - 273	-273 to 1735°C
6	Engine Intercooler Temp	1°C/bit - 40	-40 to 210°C
7	Engine Intercooler Thermostat	0.4%/bit	0-100%

Parsing Coolant Temperature:

int16_t coolant_temp = data[0] - 40;  // Range: -40°C to +210°C

LFE (65266) - Fuel Economy

Fuel consumption data. Transmitted at 100ms intervals.

Byte	Parameter	Resolution	Range
0-1	Fuel Rate	0.05 L/h per bit	0-3212.75 L/h
2-3	Instantaneous Fuel Economy	1/512 km/L per bit	0-125.5 km/L
4-5	Average Fuel Economy	1/512 km/L per bit	0-125.5 km/L
6	Throttle Position	0.4%/bit	0-100%
7	Reserved	-	-

Parsing Fuel Rate:

uint16_t fuel_raw = data[0] | (data[1] << 8);
float fuel_rate_lph = fuel_raw * 0.05;  // Liters per hour

ETC2 (61445) - Electronic Transmission Controller 2

Transmission data (optional).

Byte	Parameter	Resolution	Range
0	Selected Gear	-	-125 to 125
1-2	Current Gear Ratio	0.001/bit	0-64.255
3	Current Gear	-	-125 to 125
4-5	Transmission Range	2 bits per state	-

Error Values

J1939 uses special values to indicate errors or unavailable data:

Value	Meaning
0xFE	Parameter error
0xFF	Not available
0xFFFE (16-bit)	Parameter error
0xFFFF (16-bit)	Not available

Always check for these values before using data:

if (data[0] != 0xFF) {
    coolant_temp = data[0] - 40;
} else {
    // Data not available
}

CAN Hardware Configuration

The SKEAZ128 MSCAN peripheral is configured for:

• Bit Rate: 250 kbit/s

• Sample Point: ~75%

• Bus Timing: Prescaler depends on bus clock

Filter Configuration

The firmware accepts all J1939 messages (no filtering). In a production system, you may want to filter for specific PGNs:

// Example: Accept only EEC1, ET1, LFE
CAN1_SetAcceptanceFilter(PGN_EEC1 << 8, 0x00FFFF00);
CAN1_SetAcceptanceFilter(PGN_ET1 << 8, 0x00FFFF00);
CAN1_SetAcceptanceFilter(PGN_LFE << 8, 0x00FFFF00);

Wiring

Standard CAN bus wiring:

Pin	Function	Color (typical)
CAN_H	CAN High	Yellow
CAN_L	CAN Low	Green
GND	Ground	Black

Termination: 120Ω resistor between CAN_H and CAN_L at each end of the bus.

Debugging with PCAN

Use the CAN viewer tool to monitor live data:

python tools/can_viewer.py

Or validate CAN data against ECU telemetry:

python tools/can_validate.py --duration 10 --tolerance 5

Message Timing

Expected message rates from a typical diesel ECU:

PGN	Rate	Use Case
EEC1	10-20ms	Engine speed control
ET1	1000ms	Temperature monitoring
LFE	100ms	Fuel calculation

The PPG samples CAN data continuously and uses the most recent values for fuel calculations.