J2534 / CANbus Protocol Reference

Targeting: Adafruit Feather M4 CAN Express (SAME51) — for building a Pass-Thru style read/write .bin interface.

1. Hardware — Feather M4 CAN Express

2. CAN Bus Basics

┌─────────┬────────┬─────┬───────────────┬─────┬─────┬─────────┐
│  SOF    │  ID    │ RTR │  DLC (0-8)    │DATA │ CRC │ ACK/EOF │
│ 1 bit   │11/29b  │1 bit│  4 bits       │0-8B │15b  │         │
└─────────┴────────┴─────┴───────────────┴─────┴─────┴─────────┘

3. Arduino CAN Setup & Code

Library

Install "Adafruit CAN" (CANSAME5x) via Arduino Library Manager. Board selection: Feather M4 CAN (SAME51).

Sender Example

#include <CANSAME5x.h>

CANSAME5x CAN;

void setup() {
  Serial.begin(115200);
  while (!Serial) delay(10);

  pinMode(PIN_CAN_STANDBY, OUTPUT);
  digitalWrite(PIN_CAN_STANDBY, false);  // transceiver out of standby
  pinMode(PIN_CAN_BOOSTEN, OUTPUT);
  digitalWrite(PIN_CAN_BOOSTEN, true);   // enable 5V boost

  if (!CAN.begin(250000)) {              // 250 kbps — must match all nodes
    Serial.println("CAN init failed!");
    while (1) delay(10);
  }
  Serial.println("CAN TX ready");
}

void loop() {
  // Send a standard 11-bit ID packet
  CAN.beginPacket(0x12);        // CAN ID = 0x12
  CAN.write('H');
  CAN.write('i');
  CAN.endPacket();

  delay(100);
}

Receiver Example

#include <CANSAME5x.h>

CANSAME5x CAN;

void setup() {
  Serial.begin(115200);
  while (!Serial) delay(10);

  pinMode(PIN_CAN_STANDBY, OUTPUT);
  digitalWrite(PIN_CAN_STANDBY, false);
  pinMode(PIN_CAN_BOOSTEN, OUTPUT);
  digitalWrite(PIN_CAN_BOOSTEN, true);

  if (!CAN.begin(250000)) {
    Serial.println("CAN init failed!");
    while (1) delay(10);
  }
  Serial.println("CAN RX ready");
}

void loop() {
  int packetSize = CAN.parsePacket();
  if (packetSize) {
    Serial.print("ID: 0x");
    Serial.print(CAN.packetId(), HEX);
    Serial.print("  DLC: ");
    Serial.print(packetSize);
    Serial.print("  Data: ");
    while (CAN.available()) {
      Serial.print((char)CAN.read());
    }
    Serial.println();
  }
}

4. J2534 Pass-Thru Protocol Overview

┌──────────────┐     USB      ┌─────────────────┐    OBD-II    ┌───────┐
│  PC / OEM    │ ◄──────────► │  J2534 Device    │ ◄──────────► │  ECU  │
│  Application │   J2534 DLL  │  (Pass-Thru HW)  │   CAN bus   │       │
└──────────────┘              └─────────────────┘              └───────┘

5. J2534 API Functions

Function Prototypes

long PassThruOpen(void *pName, unsigned long *pDeviceID);
long PassThruClose(unsigned long DeviceID);

long PassThruConnect(unsigned long DeviceID, unsigned long ProtocolID,
                     unsigned long Flags, unsigned long BaudRate,
                     unsigned long *pChannelID);
long PassThruDisconnect(unsigned long ChannelID);

long PassThruReadMsgs(unsigned long ChannelID, PASSTHRU_MSG *pMsg,
                      unsigned long *pNumMsgs, unsigned long Timeout);

long PassThruWriteMsgs(unsigned long ChannelID, PASSTHRU_MSG *pMsg,
                       unsigned long *pNumMsgs, unsigned long Timeout);

long PassThruStartMsgFilter(unsigned long ChannelID, unsigned long FilterType,
                            PASSTHRU_MSG *pMaskMsg, PASSTHRU_MSG *pPatternMsg,
                            PASSTHRU_MSG *pFlowControlMsg, unsigned long *pFilterID);

long PassThruIoctl(unsigned long ChannelID, unsigned long IoctlID,
                   void *pInput, void *pOutput);

6. PASSTHRU_MSG Structure

typedef struct {
    unsigned long ProtocolID;       // Protocol for this message
    unsigned long RxStatus;         // Receive status flags
    unsigned long TxFlags;          // Transmit option flags
    unsigned long Timestamp;        // Timestamp in microseconds
    unsigned long DataSize;         // Number of bytes in Data[]
    unsigned long ExtraDataIndex;   // Start of extra data (e.g. CRC)
    unsigned char Data[4128];       // Message payload
} PASSTHRU_MSG;

Protocol IDs

TX Flags

RX Status Flags

7. Error Codes

8. Supported Protocols & Baud Rates

9. UDS Services for Read/Write .bin Files

10. Connection & Flash Flow

J2534 Initialization Sequence

1. PassThruOpen()                          → get DeviceID
2. PassThruConnect(DeviceID,
       ISO15765,                           // ProtocolID = 0x06
       0,                                  // Flags (0 = 11-bit CAN ID)
       500000,                             // Baud rate
       &channelID)                         → get ChannelID
3. PassThruStartMsgFilter(channelID,
       FLOW_CONTROL_FILTER,                // FilterType
       &maskMsg,                           // Mask: which bits to check
       &patternMsg,                        // Pattern: ECU response ID (e.g. 0x7E8)
       &flowControlMsg,                    // Flow control: tester ID (e.g. 0x7E0)
       &filterID)
4. PassThruIoctl(SET_CONFIG, ...)          → set timing params (P1–P4, etc.)

Write .bin to ECU (Download)

1. UDS 0x10 0x02          → Enter Programming Session
2. UDS 0x27 0x01          → SecurityAccess: request seed
3. UDS 0x27 0x02 [key]    → SecurityAccess: send key
4. UDS 0x31 [erase]       → RoutineControl: erase flash region
5. UDS 0x34 [addr][size]  → RequestDownload: specify address & total size
                             Response contains max block length
6. Loop:
   UDS 0x36 [blockN][data]→ TransferData: send .bin in chunks
7. UDS 0x37               → RequestTransferExit
8. UDS 0x11 0x01          → ECUReset (hard reset)

Read .bin from ECU (Upload)

1. UDS 0x10 0x02          → Enter Programming Session
2. UDS 0x27 0x01/0x02     → SecurityAccess (seed/key)
3. UDS 0x35 [addr][size]  → RequestUpload: specify address & size
                             Response contains max block length
4. Loop:
   UDS 0x36 [blockN]      → TransferData: receive .bin chunks
   Save chunks to file
5. UDS 0x37               → RequestTransferExit
6. UDS 0x11 0x01          → ECUReset

11. Mapping J2534 API → M4 Feather CAN

12. Sources

• Adafruit — Feather M4 CAN Arduino Examples
• Adafruit — Feather M4 CAN Overview
• Adafruit — Feather M4 CAN Express Product Page
• Kvaser — Introduction to SAE J2534
• SAE J2534 Pass-Thru API Technical Reference
• J2534 v04.04 Header File (GitHub)
• AutoPi — J2534 Pass-Thru Explained
• OpenJ2534 Resources (GitHub)
• CSS Electronics — UDS Protocol Tutorial
• Wikipedia — Unified Diagnostic Services
• PEAK — PCAN-PassThru API
• Softing — PassThru API (SAE J2534)

Reference compiled March 2026. SAE J2534 v04.04 specification. For official details, obtain the full SAE standard document.