Chapter 189: DeviceNet Protocol Implementation

Chapter Objectives

By the end of this chapter, you will be able to:

• Understand the fundamentals of the DeviceNet protocol and its relationship with CAN and CIP.
• Describe the DeviceNet network architecture, including physical layer specifications (cabling, connectors, power).
• Explain DeviceNet communication mechanisms: I/O messages (cyclic) and Explicit messages (acyclic).
• Understand the concept of the Common Industrial Protocol (CIP) Object Model as used in DeviceNet.
• Recognize the role and structure of Electronic Data Sheet (EDS) files.
• Outline the hardware requirements for connecting an ESP32 to a DeviceNet network, focusing on the TWAI (CAN) interface.
• Discuss conceptual software approaches for implementing a DeviceNet slave device on an ESP32.
• Appreciate the differences among ESP32 variants concerning their suitability for DeviceNet implementation.
• Be aware of common challenges and troubleshooting techniques in DeviceNet slave development.

Introduction

Continuing our journey through industrial communication protocols, we now focus on DeviceNet. DeviceNet is an open automation standard developed by Allen-Bradley (now Rockwell Automation) and managed by ODVA (Open DeviceNet Vendors Association). It is a robust and widely adopted network designed to connect industrial devices like sensors, actuators, motor starters, and simple control devices to higher-level controllers like PLCs.

DeviceNet is built upon the Controller Area Network (CAN) physical and data link layers, which we explored in Chapters 151-155 (TWAI). Above CAN, DeviceNet utilizes the Common Industrial Protocol (CIP) for its application layer. This layered approach allows DeviceNet to leverage the cost-effectiveness and robustness of CAN while providing a rich set of services and object-oriented data representation suitable for industrial automation.

For ESP32 developers, DeviceNet presents an opportunity to integrate their devices into established industrial control systems. The ESP32’s built-in TWAI (Two-Wire Automotive Interface) controller, which is CAN 2.0B compatible, provides the necessary hardware foundation. This chapter will delve into the core concepts of DeviceNet and explore how an ESP32, using ESP-IDF v5.x, can be conceptually developed into a DeviceNet slave device.

Theory

DeviceNet Overview

DeviceNet is a digital, multi-drop network that connects and serves as a communication network between industrial controllers and I/O devices. It offers a cost-effective solution for distributing and managing devices on a plant floor.

Key Features:

• CAN-based: Utilizes the CAN protocol (ISO 11898-1) for Layer 1 (Physical) and Layer 2 (Data Link). This provides excellent noise immunity and error detection/handling capabilities.
• CIP Application Layer: Employs the Common Industrial Protocol (CIP) for the upper layers (Session, Presentation, Application). CIP is also used by other ODVA networks like EtherNet/IP and ControlNet, allowing for a degree of interoperability and a common object model.
• Producer-Consumer Model: DeviceNet uses a producer-consumer model for data exchange. A device (producer) makes data available on the network, and any number of other devices (consumers) can access that data.
• Network Power: DeviceNet specifications allow for power to be supplied over the network cable to low-power devices, simplifying wiring.
• Device Profiles: Standardized profiles exist for common device types (e.g., limit switches, photoelectric sensors, motor starters), ensuring interoperability between devices from different vendors.

Physical Layer

DeviceNet specifies the physical layer based on CAN, with some particular choices:

• Baud Rates: Supports 125 kbps, 250 kbps, and 500 kbps. The choice of baud rate affects the maximum network length.
  • 125 kbps: up to 500 meters
  • 250 kbps: up to 250 meters
  • 500 kbps: up to 100 meters
• Cabling: Uses shielded twisted-pair cable. Typically, two pairs are used: one for CAN_H and CAN_L signals, and one for network power (V+ and V-).
  • Thick trunk cable for main network segments.
  • Thin drop cable for connecting individual devices to the trunk.
• Connectors: Standardized connectors are defined:
  • Open-Style (Screw Terminal): For direct wiring.
  • Mini-Style (7/8″): Robust, sealed connectors for trunk lines.
  • Micro-Style (M12): Smaller, sealed connectors common for drop lines and sensors.

• Termination: Like any CAN bus, DeviceNet requires 120-ohm termination resistors at both physical ends of the trunk line.
• Network Power: The cable can carry 24V DC power. Devices can be powered directly from the network or have their own power supply. Specifications exist for current limits and power distribution.

Data Link Layer (CAN)

DeviceNet uses standard CAN 2.0A (11-bit identifiers) or CAN 2.0B (29-bit identifiers, though 11-bit is more common for basic I/O).

• Message Identifiers (CAN IDs): DeviceNet defines a specific scheme for allocating CAN IDs to devices and message types. This is crucial for message prioritization and routing.
  • Each device on the network has a unique MAC ID (Media Access Control Identifier) or node address, ranging from 0 to 63.
  • The CAN ID encodes the message type, MAC ID of the producing device, and sometimes other information.
• Error Handling: Leverages CAN’s robust error detection (CRC, bit stuffing, frame checks) and fault confinement mechanisms (error counters, bus-off state).

Application Layer (CIP – Common Industrial Protocol)

CIP is an object-oriented protocol that defines how devices represent themselves and their data on the network.

• Object Model: Devices are modeled as a collection of Objects. Each object is an instance of a Class and represents a specific component or function of the device (e.g., Identity Object, Connection Object, Application-specific Objects).
  • Class: A template defining the structure and behavior of objects of that type.
  • Instance: A specific occurrence of a class.
  • Attribute: A data item within an object that represents a characteristic or status (e.g., Vendor ID, Product Name, Sensor Value).
  • Service: A command or function that can be performed on an object or class (e.g., Get_Attribute_Single, Set_Attribute_Single).

%%{ init: { 'theme': 'base', 'themeVariables': { 'fontFamily': 'Open Sans, sans-serif' } } }%%
graph TD
    subgraph "DeviceNet Slave Device (MAC ID: 5)"
        direction LR
        O1[("<b>Identity Object</b><br>(Class 0x01, Inst 1)")]
        O3[("<b>DeviceNet Object</b><br>(Class 0x03, Inst 1)")]
        O4[("<b>Assembly Object</b><br>(Class 0x04)")]
        O_APP[("<b>Application Object</b><br><i>(e.g., Temp Sensor)</i>")]
    end

    subgraph "Zoom into: Identity Object"
        direction TB
        Instance(("<b>Instance 1</b><br><i>The actual object in the device</i>"))
        Class[("<b>Class: Identity</b><br><i>Template for all Identity Objects</i>")]
        
        subgraph "Instance Attributes"
            A1["Attr 1: Vendor ID"]
            A2["Attr 2: Device Type"]
            A3["Attr 3: Product Code"]
            A7["Attr 7: Serial Number"]
        end

        subgraph "Services (Actions)"
            S1["Get_Attribute_Single"]
            S2["Set_Attribute_Single"]
            S_ALL["Get_Attribute_All"]
        end

        Instance -- "Is an instance of" --> Class
        Instance -- "Has Data" --> A1
        Instance -- "Has Data" --> A2
        Instance -- "Has Data" --> A3
        Instance -- "Has Data" --> A7
        S1 -- "Act on" --> Instance
        S2 -- "Act on" --> Instance
        S_ALL -- "Act on" --> Instance
    end

    %% Styling
    style O1 fill:#DBEAFE,stroke:#2563EB,stroke-width:1px,color:#1E40AF
    style O3 fill:#DBEAFE,stroke:#2563EB,stroke-width:1px,color:#1E40AF
    style O4 fill:#DBEAFE,stroke:#2563EB,stroke-width:1px,color:#1E40AF
    style O_APP fill:#DBEAFE,stroke:#2563EB,stroke-width:1px,color:#1E40AF

    style Instance fill:#FEF3C7,stroke:#D97706,stroke-width:2px,color:#92400E
    style Class fill:#EDE9FE,stroke:#5B21B6,stroke-width:1px,color:#5B21B6
    style A1 fill:#D1FAE5,stroke:#059669,stroke-width:1px,color:#065F46
    style A2 fill:#D1FAE5,stroke:#059669,stroke-width:1px,color:#065F46
    style A3 fill:#D1FAE5,stroke:#059669,stroke-width:1px,color:#065F46
    style A7 fill:#D1FAE5,stroke:#059669,stroke-width:1px,color:#065F46
    style S1 fill:#FEE2E2,stroke:#DC2626,stroke-width:1px,color:#991B1B
    style S2 fill:#FEE2E2,stroke:#DC2626,stroke-width:1px,color:#991B1B
    style S_ALL fill:#FEE2E2,stroke:#DC2626,stroke-width:1px,color:#991B1B

• Key CIP Objects in DeviceNet:
  • Identity Object (Class Code 0x01): Provides information about the device (Vendor ID, Device Type, Product Code, Revision, Serial Number, etc.). Mandatory.
  • Message Router Object (Class Code 0x02): Handles routing of explicit messages. Mandatory.
  • DeviceNet Object (Class Code 0x03): Manages DeviceNet-specific parameters like MAC ID, baud rate, and connection information. Mandatory.
  • Assembly Object (Class Code 0x04): Defines groupings of attributes from different objects to be exchanged as I/O data (PDOs in CANopen terms, but called I/O messages in DeviceNet).
  • Connection Object (Class Code 0x05): Manages the establishment and configuration of communication connections.
  • Application-Specific Objects: Defined by device profiles or vendors for specific device functionality (e.g., a Temperature Sensor Object).

DeviceNet Communication

DeviceNet supports two primary types of communication:

%%{ init: { 'theme': 'base', 'themeVariables': { 'fontFamily': 'Open Sans, sans-serif' } } }%%
sequenceDiagram
    actor Master as Master (Scanner)
    actor Slave as Slave (Adapter)

    Note over Master, Slave: I/O Messages (Cyclic/COS) - Real-Time Data
    loop Every X ms or on data change
        Slave->>+Master: I/O Data (e.g., Sensor Values)
        Master-->>-Slave: I/O Data (e.g., Actuator Commands)
    end

    Note over Master, Slave: Explicit Messaging Example (Acyclic Read)
    par 
        Master->>+Slave: Explicit Request (e.g., Get_Attribute_Single VendorID)
        Note right of Slave: Slave processes request,<br>accesses Identity Object.
        Slave-->>-Master: Explicit Response (Value: 0x010C)
    end

    Note over Master, Slave: Explicit Messages (Acyclic) - Configuration/Diagnostics
    Master->>+Slave: Explicit Request (e.g., Set_Attribute_Single 'App Parameter')
    Note right of Slave: Slave validates and<br>applies the new parameter.
    Slave-->>-Master: Explicit Response (Success/Error)

1. I/O Messages (Implicit or Cyclic):
   • Used for fast, real-time exchange of process data (inputs and outputs).
   • Data is produced by one device and consumed by one or more other devices.
   • Typically transmitted cyclically or on change-of-state.
   • Use predefined CAN IDs based on the producer’s MAC ID and connection configuration.
   • The data content is defined by Assembly Objects.
   • Types of I/O Connections:
     • Poll: Master requests data from slave.
     • Bit-Strobe: Master sends a command, slaves respond with 1-bit to 8-bits of data. Efficient for many simple devices.
     • Change-of-State (COS): Device sends data only when it changes significantly or after a heartbeat timer expires.
     • Cyclic: Device sends data at a fixed periodic rate.
2. Explicit Messages (Acyclic):
   • Used for point-to-point communication, typically for configuration, diagnostics, or less time-critical data exchange.
   • Allow access to any object and attribute within a device using CIP services (e.g., Get_Attribute_Single, Set_Attribute_Single).
   • Involve a request from a client (e.g., master/scanner) and a response from a server (e.g., slave/adapter).
   • Can be fragmented if the data exceeds the CAN frame payload size (8 bytes).
   • UCMM (UnConnected Message Manager): Some explicit messages can be sent without a pre-established connection, often used for device discovery or initial configuration.

DeviceNet Connections

• Predefined Master/Slave Connection Set (Group 1 & Group 2 Only Messages):
  • A simplified connection scheme primarily for Group 2 Only Server devices (simple I/O slaves).
  • Group 1 messages are for high-priority I/O.
  • Group 2 messages are for other I/O and explicit messages.
• Group 3 and Unconnected Messages: For more flexible communication, often used by more intelligent devices.

Electronic Data Sheet (EDS) Files

• Purpose: An EDS file is a human-readable text file that describes the DeviceNet capabilities and configurable parameters of a device.
• Content:
  • Device identification (Vendor ID, Product Code, etc.).
  • Supported baud rates.
  • I/O connection types and assembly instance information.
  • Configuration parameters (CIP object attributes that can be set).
  • Device classification (e.g., “Sensor,” “Drive”).
• Format: INI-style text file with sections and keywords.
• Role: The DeviceNet master’s configuration software uses the EDS file to understand the slave device, configure it, and establish communication.

Implementing DeviceNet on ESP32

The ESP32’s TWAI controller can handle the CAN physical and data link layer aspects of DeviceNet. The more significant challenge lies in implementing the CIP application layer and the DeviceNet object behaviors.

Hardware Requirements:

• ESP32 Microcontroller: Any variant with a TWAI controller.
• CAN Transceiver: An external CAN transceiver IC (e.g., MCP2551, TJA1050, SN65HVD230) is required to interface the ESP32’s TWAI controller pins (TX, RX) with the differential CAN bus (CAN_H, CAN_L).
• DeviceNet Connector: Appropriate connector (e.g., M12 5-pin, open-style) for the DeviceNet cable.
• Power Supply: The ESP32 device might be powered from the DeviceNet bus (if low power) or have its own supply.

Software Approach Considerations:

1. Full Software Stack (Complex): Developing a DeviceNet slave stack from scratch on the ESP32. This involves:
   • Managing the TWAI interface (message filtering, transmission, reception).
   • Implementing the CIP object model (Identity, Message Router, DeviceNet Object, Assembly Objects, Connection Objects, application-specific objects).
   • Handling I/O message production/consumption.
   • Processing Explicit messages (requests/responses).
   • Managing the DeviceNet state machine (online/offline, duplicate MAC ID check).
   • Parsing/using EDS file information (conceptually, as the master uses the EDS).This is a substantial software engineering effort.
2. Using an Existing Open-Source Stack:
   • There are some open-source CANopen stacks (e.g., CanFestival, CANopenNode) that share similarities with DeviceNet due to both using CAN and object dictionaries. However, CIP and DeviceNet specifics are different.
   • Dedicated open-source DeviceNet slave stacks for general MCUs are less common or might be less mature than commercial offerings. Porting such a stack to ESP-IDF would be necessary.
3. Using a Commercial Stack:
   • Several companies offer commercial DeviceNet slave stacks for various microcontrollers. These provide a tested, compliant solution and often come with tools for EDS file generation and configuration. This is the recommended route for products requiring certification and high reliability.
   • A commercial stack would provide an API for the ESP32 application to interact with, handling the DeviceNet protocol details internally.

Tip: ODVA provides conformance testing for DeviceNet products. Using a pre-certified stack or undergoing conformance testing is crucial for ensuring interoperability in industrial environments.

Practical Examples

This section will focus on initializing the ESP32’s TWAI interface for CAN communication and then conceptually discuss how a DeviceNet slave stack would build upon this foundation.

Hardware Setup

1. ESP32 Development Board.
2. CAN Transceiver Module: A module based on MCP2551, TJA1050, or similar.
3. Connections (ESP32 to CAN Transceiver):
   • ESP32 TWAI TX pin -> Transceiver TXD pin
   • ESP32 TWAI RX pin <- Transceiver RXD pin
   • Transceiver VCC -> ESP32 3.3V or 5V (check transceiver datasheet)
   • Transceiver GND -> ESP32 GND
   • Transceiver CAN_H and CAN_L lines -> DeviceNet network.
4. DeviceNet Master: A PLC with a DeviceNet scanner module, a PC with a DeviceNet interface card and master software (e.g., Rockwell RSNetWorx for DeviceNet).
5. DeviceNet Cable and Termination: Properly cabled DeviceNet segment with 120-ohm terminators at each end.

Software: ESP32 TWAI Initialization and Conceptual DeviceNet Slave Interaction

Project Setup in VS Code

1. Create a new ESP-IDF v5.x project (e.g., esp32_devicenet_slave).
2. The DeviceNet stack would be a separate component or library.

EDS File Creation (Conceptual Snippet)

An EDS file is crucial for the master to recognize and configure the ESP32 slave. Below is a highly simplified conceptual snippet.

; Simplified EDS File Snippet for a hypothetical ESP32 DeviceNet Slave
; File: ESP32DNET.EDS

[File]
    DescText    = "ESP32 DeviceNet Slave Demo EDS";
    CreateDate  = 06-04-2025;
    CreateTime  = 12:00:00;
    Revision    = 1.0;

[Device]
    VendCode    = 0x010C;       ; Hypothetical Vendor Code for Espressif EDU
    ProdType    = 0;            ; Generic Device (Type 0)
    ProdCode    = 0x0001;       ; Product Code for this specific device
    MajRev      = 1;
    MinRev      = 0;
    VendName    = "Espressif Systems EDU";
    ProdName    = "ESP32 DNet Slave Demo";
    Catalog     = "ESP32-DNET-SLV-DEMO";

    DeviceType  = "Generic Device"; ; Or more specific like "Digital I/O Module"

    ParamClass = 0x0F;         ; Parameters section below
    ParamInst  = 1;

[Params]                        ; Example parameters
    Param1 = 0,                 ; Configurable parameter 1
             USINT,             ; Data type: Unsigned Short Integer
             0,                 ; Min value
             255,               ; Max value
             0,                 ; Default value
             0,                 ; Scaling factor (ignored)
             0,                 ; Scaling divisor (ignored)
             0,                 ; Units (ignored)
             "App Parameter 1", ; Name
             "",                ; Help string
             "";                ; Path (for structured params)

[IO_Info]
    Default = 0x0000;           ; Default connection path
    Input1 = 2,                 ; Size of input data in bytes (Consumed by master)
             0x20, 0x04, 0x24, 0x64, 0x2C, 0x65; ; Example Path for Input Assembly 100 (Instance 0x64)
                                                ; (Path: Class 4, Instance 100, Attribute 3)
    Output1 = 2,                ; Size of output data in bytes (Produced by master)
              0x20, 0x04, 0x24, 0x96, 0x2C, 0x66; ; Example Path for Output Assembly 150 (Instance 0x96)
                                                ; (Path: Class 4, Instance 150, Attribute 3)
    Poll = 1;                   ; Supports Polled I/O
    COS  = 1;                   ; Supports Change-of-State I/O
    Cyclic = 1;                 ; Supports Cyclic I/O

; Sections for Assembly objects, Connection Manager objects, etc. would also be here.

Warning: Creating a correct EDS file requires careful study of the ODVA DeviceNet specification. The example above is illustrative and incomplete. EDS generator tools are often used.

Main Application Code (main/main.c)

This code focuses on initializing the TWAI peripheral and simulating where interactions with a DeviceNet stack would occur.

#include <stdio.h>
#include <string.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_system.h"
#include "esp_log.h"
#include "driver/twai.h" // For CAN communication
#include "driver/gpio.h"

// Hypothetical DeviceNet slave stack header - NOT a real file for this example
// #include "devicenet_slave_stack.h"

static const char *TAG = "DNET_APP";

// Configuration for TWAI (CAN)
// These GPIOs are examples; check your ESP32 board/module for actual TWAI pins
#define TWAI_TX_GPIO    GPIO_NUM_21 // Example TX pin
#define TWAI_RX_GPIO    GPIO_NUM_22 // Example RX pin

// DeviceNet MAC ID for this slave (0-63)
#define DEVICENET_MAC_ID 5

// Application Process Data (example: 2 bytes IN, 2 bytes OUT)
// These would be managed by the DeviceNet stack based on EDS/configuration.
uint8_t g_devicenet_input_data[2];  // Data ESP32 (slave) sends to Master (scanner)
uint8_t g_devicenet_output_data[2]; // Data ESP32 (slave) receives from Master (scanner)

// --- Hypothetical Callback Functions (would be part of a DeviceNet stack API) ---
/**
 * @brief Callback invoked by the DeviceNet stack when new output I/O data is received.
 *
 * @param data Pointer to the received output data.
 * @param len Length of the received data.
 */
void app_dnet_output_io_received_cb(const uint8_t *data, uint8_t len) {
    if (data && len == sizeof(g_devicenet_output_data)) {
        memcpy(g_devicenet_output_data, data, len);
        ESP_LOGI(TAG, "DeviceNet Output I/O received (len %d): 0x%02X 0x%02X",
                 len, g_devicenet_output_data[0], g_devicenet_output_data[1]);
        // TODO: Application logic to act on received output data
    }
}

/**
 * @brief Callback invoked by the DeviceNet stack when it needs input I/O data to send.
 *
 * @param buffer Pointer to the buffer where application should write its input data.
 * @param max_len Maximum length of the buffer.
 * @return uint8_t Actual length of the input data written.
 */
uint8_t app_dnet_prepare_input_io_data_cb(uint8_t *buffer, uint8_t max_len) {
    if (buffer && max_len >= sizeof(g_devicenet_input_data)) {
        // TODO: Application logic to prepare input data (e.g., read sensors)
        // For demonstration, we'll just use the global buffer
        memcpy(buffer, g_devicenet_input_data, sizeof(g_devicenet_input_data));
        return sizeof(g_devicenet_input_data);
    }
    return 0;
}

/**
 * @brief Callback for explicit message requests (e.g., Get_Attribute_Single).
 * This is highly simplified. A real stack would handle object/attribute access.
 *
 * @param class_id CIP Class ID.
 * @param instance_id CIP Instance ID.
 * @param attribute_id CIP Attribute ID.
 * @param service_code CIP Service Code.
 * @param request_data Pointer to request data.
 * @param request_len Length of request data.
 * @param response_buffer Buffer to write response.
 * @param max_response_len Max length of response buffer.
 * @return uint16_t Length of actual response data, or 0 on error.
 */
// uint16_t app_dnet_explicit_message_cb(uint16_t class_id, uint16_t instance_id, uint8_t attribute_id,
//                                      uint8_t service_code, const uint8_t* request_data, uint16_t request_len,
//                                      uint8_t* response_buffer, uint16_t max_response_len) {
//    ESP_LOGI(TAG, "Explicit Message Rcvd: Cls:0x%02X, Inst:0x%02X, Attr:0x%02X, Svc:0x%02X",
//             class_id, instance_id, attribute_id, service_code);
//    // TODO: Implement object dictionary access based on class/instance/attribute
//    // Example: if (class_id == IDENTITY_CLASS && service_code == GET_ATTRIBUTE_SINGLE) { ... }
//    return 0; // Placeholder
// }

// --- End of Hypothetical Callbacks ---

static void initialize_twai_for_devicenet(twai_timing_config_t *timing_config) {
    //Initialize TWAI general config
    twai_general_config_t g_config = TWAI_GENERAL_CONFIG_DEFAULT(TWAI_TX_GPIO, TWAI_RX_GPIO, TWAI_MODE_NORMAL);
    //Initialize TWAI timing config (passed as argument, e.g., for 125k, 250k, 500k)
    //Initialize TWAI filter config - Accept all messages for a slave initially, stack would refine.
    twai_filter_config_t f_config = TWAI_FILTER_CONFIG_ACCEPT_ALL();

    //Install TWAI driver
    if (twai_driver_install(&g_config, timing_config, &f_config) == ESP_OK) {
        ESP_LOGI(TAG, "TWAI Driver installed");
    } else {
        ESP_LOGE(TAG, "Failed to install TWAI driver");
        return;
    }

    //Start TWAI driver
    if (twai_start() == ESP_OK) {
        ESP_LOGI(TAG, "TWAI Driver started");
    } else {
        ESP_LOGE(TAG, "Failed to start TWAI driver");
    }
}

void devicenet_slave_task(void *pvParameters) {
    ESP_LOGI(TAG, "DeviceNet Slave Application Task Started.");

    // Initialize global I/O data buffers (example values)
    g_devicenet_input_data[0] = 0x01;
    g_devicenet_input_data[1] = 0x02;
    memset(g_devicenet_output_data, 0, sizeof(g_devicenet_output_data));

    // --- Conceptual DeviceNet Stack Initialization ---
    // This is where a real DeviceNet slave stack would be configured and started.
    // It would take the MAC ID, pointers to I/O data, and callbacks.
    // devicenet_slave_config_t dnet_config = {
    //     .mac_id = DEVICENET_MAC_ID,
    //     .baud_rate_kbits = 500, // Or configured via EDS/LSS
    //     .vendor_id = 0x010C,    // From EDS
    //     .product_code = 0x0001, // From EDS
    //     // Assign callback functions
    //     .output_io_received_cb = app_dnet_output_io_received_cb,
    //     .prepare_input_io_data_cb = app_dnet_prepare_input_io_data_cb,
    //     .explicit_message_cb = app_dnet_explicit_message_cb,
    //     // Pointers to data buffers or configuration for Assembly objects
    // };

    // if (devicenet_slave_stack_init(&dnet_config) != ESP_OK) {
    //     ESP_LOGE(TAG, "Failed to initialize DeviceNet slave stack!");
    //     vTaskDelete(NULL); return;
    // }

    // if (devicenet_slave_stack_start() != ESP_OK) { // Go online
    //     ESP_LOGE(TAG, "Failed to start DeviceNet slave stack (go online)!");
    //     vTaskDelete(NULL); return;
    // }
    ESP_LOGW(TAG, "Conceptual DeviceNet stack functions are commented out.");
    ESP_LOGW(TAG, "This example focuses on TWAI setup and application data handling concepts.");
    ESP_LOGI(TAG, "A real implementation requires a dedicated DeviceNet slave stack component.");
    // --- End of Conceptual Stack Initialization ---

    uint8_t counter = 0;
    while (1) {
        // Application logic runs here.
        // Update g_devicenet_input_data based on sensor readings, internal state, etc.
        g_devicenet_input_data[0] = counter++;
        g_devicenet_input_data[1] = (g_devicenet_output_data[0] ^ 0xFF); // Example: reflect inverted output

        // The DeviceNet stack would handle TWAI message reception and transmission
        // based on received messages from the master and data prepared by the application.
        // It would call registered callbacks (like app_dnet_output_io_received_cb) upon relevant events.

        // For explicit messages, the stack would parse requests and call app_dnet_explicit_message_cb
        // to get data from the application's object dictionary representation.

        // Simulate stack interaction (in a real system, stack drives this)
        app_dnet_prepare_input_io_data_cb(NULL, 0); // Conceptual: stack would get data
        app_dnet_output_io_received_cb(NULL, 0);    // Conceptual: stack would provide data

        ESP_LOGD(TAG, "App Loop: Inputs (0x%02X, 0x%02X), Outputs (0x%02X, 0x%02X)",
                 g_devicenet_input_data[0], g_devicenet_input_data[1],
                 g_devicenet_output_data[0], g_devicenet_output_data[1]);

        vTaskDelay(pdMS_TO_TICKS(200)); // Application logic cycle
    }
}

void app_main(void) {
    // Initialize NVS - often a prerequisite, good practice.
    // esp_err_t ret = nvs_flash_init(); ...

    // Configure TWAI timing for a DeviceNet baud rate (e.g., 500kbps)
    // Standard prescalers for ESP32 (80MHz APB clock):
    // 125kbps: BRP=32, TSEG1=15, TSEG2=4, SJW=3  (actual rate: 125kbps, sample point 80.0%)
    // 250kbps: BRP=16, TSEG1=15, TSEG2=4, SJW=3  (actual rate: 250kbps, sample point 80.0%)
    // 500kbps: BRP=8,  TSEG1=15, TSEG2=4, SJW=3  (actual rate: 500kbps, sample point 80.0%)
    // For ESP32-C3/S3 (40MHz APB clock, if TWAI_CLK_SRC_DEFAULT is used):
    // 125kbps: BRP=16, TSEG1=15, TSEG2=4, SJW=3
    // 250kbps: BRP=8,  TSEG1=15, TSEG2=4, SJW=3
    // 500kbps: BRP=4,  TSEG1=15, TSEG2=4, SJW=3
    // Check specific ESP32 variant datasheet for TWAI clock source and adjust BRP accordingly.
    // The example below assumes an 80MHz APB clock for TWAI.
    twai_timing_config_t t_config = TWAI_TIMING_CONFIG_500KBITS(); // Or _250KBITS or _125KBITS

    initialize_twai_for_devicenet(&t_config);

    xTaskCreate(devicenet_slave_task, "dnet_slave_task", 4096, NULL, 5, NULL);
}

main/CMakeLists.txt

idf_component_register(SRCS "main.c"
                       INCLUDE_DIRS ".")

Build Instructions

1. Save main.c in the main directory.
2. Save CMakeLists.txt in the main directory.
3. If using a real DeviceNet stack component, add it to your project’s components directory or as a dependency.
4. Open the project in VS Code with the ESP-IDF extension.
5. Select the correct ESP32 target and configure TWAI GPIO pins if different from defaults in menuconfig (ESP-IDF: SDK Configuration editor).
6. Build the project (ESP-IDF: Build your project).

Run/Flash/Observe Steps

1. Flash the compiled firmware to your ESP32 board.
2. Connect the ESP32 (via its CAN transceiver) to the DeviceNet network, ensuring the Master and other devices are also connected, and the bus is properly terminated.
3. In your DeviceNet Master configuration tool:
   • Add the ESP32 slave to the network scan list using its MAC ID (e.g., 5) and the corresponding EDS file.
   • Configure the master to establish I/O connections with the ESP32 slave.
   • Bring the DeviceNet network online.
4. Open the ESP-IDF Monitor tool (ESP-IDF: Monitor your device) to observe log messages from the ESP32.
5. On the DeviceNet Master, observe the input data coming from the ESP32 slave and try to write output data to it. You should see the ESP32’s log messages reflecting received output data and the application logic updating its input data.

Tip: A CAN bus analyzer tool (sometimes called a “CAN sniffer”) that can decode DeviceNet messages is extremely helpful for troubleshooting. It allows you to see the raw CAN frames and how they relate to DeviceNet messages.

Variant Notes

All ESP32 variants that include a TWAI (CAN) controller are capable of handling the fundamental CAN communication required for DeviceNet.

• ESP32 (Original), ESP32-S2, ESP32-S3, ESP32-C3, ESP32-C6, ESP32-H2:
  • All these variants have at least one TWAI controller.
  • The suitability for running a full DeviceNet slave stack depends on the complexity of the stack, the required number of objects and connections, and the application logic’s demands on CPU and memory.
  • CPU Performance: More complex DeviceNet devices (e.g., those handling many explicit messages, complex object behaviors, or large I/O assemblies) will benefit from higher CPU performance (ESP32, ESP32-S3 are generally more powerful than C-series/H-series).
  • Memory (RAM/Flash): A DeviceNet stack, its object dictionary, and application code require adequate RAM and Flash. PSRAM can be beneficial for ESP32/S3 if the stack or application is memory-intensive.
  • TWAI Controller Clock Source: The TWAI peripheral’s clock source can differ between ESP32 families (e.g., APB clock, which can be 80MHz or 40MHz depending on the chip and PLL settings). This affects the brp (baud rate prescaler) calculation for TWAI timing configuration. Always consult the specific chip’s Technical Reference Manual and ESP-IDF documentation for accurate brp settings for desired DeviceNet baud rates. The TWAI_TIMING_CONFIG_XXXKBITS() macros in ESP-IDF are typically based on a default APB clock frequency (often 80MHz for ESP32, check for others). If your actual APB clock differs, you’ll need to calculate brp manually.

General Considerations:

• Stack Implementation: The primary differentiator is not the TWAI hardware itself (which is largely compatible) but the software stack’s efficiency and resource requirements when ported to a specific ESP32 variant.
• Certification: For commercial DeviceNet products, ODVA conformance testing is critical. The choice of ESP32 variant might be influenced by the resource needs of a conformant stack.

Common Mistakes & Troubleshooting Tips

Exercises

1. Exercise 1: TWAI Echo (Loopback Test)
   • Configure the ESP32’s TWAI controller in loopback mode (TWAI_MODE_NO_ACK or TWAI_MODE_LISTEN_ONLY and send to self, or use internal loopback if available in test modes, though TWAI_MODE_NORMAL with external loopback wiring is more realistic for bus testing).
   • Write a task that sends a CAN message with a specific ID and data.
   • Write another part of the task (or a separate task/ISR) that receives CAN messages.
   • Verify that the ESP32 can send and receive its own messages. This tests the basic TWAI setup.
   • Log the transmitted and received messages.
2. Exercise 2: EDS File Analysis
   • Obtain an EDS file for a simple commercial DeviceNet device (e.g., a sensor or I/O block) from a manufacturer’s website.
   • Open the EDS file in a text editor. Identify and list:
     • The Vendor ID and Product Code.
     • The default MAC ID (if specified, often it’s not and set by user).
     • The supported baud rates.
     • At least one Input Assembly instance (path and size) and one Output Assembly instance (path and size).
     • One configurable parameter from the [Params] section, noting its data type and name.
3. Exercise 3: Conceptual Explicit Message Handling
   • Imagine your ESP32 DeviceNet slave needs to respond to a Get_Attribute_Single request for its Vendor ID (Identity Object, Class 0x01, Instance 1, Attribute 1).
   • Outline the pseudo-code for the app_dnet_explicit_message_cb function (from the conceptual example) to handle this specific request. It should check the class, instance, attribute, and service code, and then prepare a response buffer containing the hypothetical Vendor ID (e.g., 0x010C).

Summary

• DeviceNet is a CAN-based industrial network that uses the Common Industrial Protocol (CIP) for its application layer, enabling robust communication between controllers and field devices.
• It specifies physical layer details like baud rates (125/250/500 kbps), cabling, connectors, and network power distribution.
• Communication involves cyclic I/O messages for real-time data and acyclic Explicit messages for configuration and diagnostics, all built upon standard CAN messaging.
• The CIP object model provides a standardized way for devices to represent their data and functionality, described by EDS files.
• ESP32 devices can interface with DeviceNet networks using their built-in TWAI (CAN) controller and an external CAN transceiver.
• Implementing a DeviceNet slave requires a software stack on the ESP32 to handle the CIP protocol, object dictionary, and DeviceNet-specific behaviors.
• Careful attention to MAC IDs, baud rates, EDS files, and the underlying CAN communication is crucial for successful DeviceNet integration.

Further Reading

• ODVA, Inc.: https://www.odva.org – Official source for DeviceNet specifications, vendor IDs, conformance testing, and technical papers. (Access to full specifications often requires membership or purchase).
• “DeviceNet Specification” (Volumes I & II): Published by ODVA.
• “The CIP Networks Library” (Volumes on CIP Common, DeviceNet Adaptation of CIP, etc.): Published by ODVA.
• ESP-IDF Programming Guide – TWAI Driver: https://docs.espressif.com/projects/esp-idf/en/v5.4/esp32/api-reference/peripherals/twai.html (Select your specific ESP32 target).
• CAN Transceiver Datasheets: (e.g., Microchip MCP2551, NXP TJA1050, TI SN65HVD23x).
• Books on Industrial Communication Networks: Many textbooks cover DeviceNet as part of broader industrial networking topics.