Chapter 191: IO-Link Master Implementation

Chapter Objectives

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

• Understand the fundamental concepts and architecture of the IO-Link communication protocol.
• Describe the role of an IO-Link Master and an IO-Link Device.
• Explain how an ESP32 can be used to control an IO-Link Master PHY (Physical Layer IC).
• Configure UART communication on the ESP32 for interfacing with an IO-Link PHY.
• Understand the basic principles of sending commands and receiving data in an IO-Link system via a PHY.
• Recognize differences in implementing IO-Link master solutions across various ESP32 variants.
• Identify common issues and troubleshoot basic IO-Link master setups.

Introduction

In modern industrial automation, the demand for smarter sensors and actuators is ever-increasing. These “smart” devices not only provide process data but also offer valuable diagnostic information and allow for on-the-fly parameterization. IO-Link is a powerful, standardized point-to-point serial communication protocol (IEC 61131-9) designed to connect these smart sensors and actuators to an automation system. It acts as a “digital highway” to the lowest level of automation, enabling seamless communication and enhanced functionality.

While the ESP32 itself doesn’t natively speak IO-Link at the physical layer (which typically involves 24V signaling), it can serve as an intelligent controller for a dedicated IO-Link Master PHY (Physical Layer) IC. This chapter explores how you can leverage the ESP32 and ESP-IDF to build an IO-Link Master solution, enabling your ESP32-based systems to communicate with a wide range of industrial IO-Link devices. This capability is crucial for applications like industrial sensor networks, factory automation, and intelligent machine control.

Theory

What is IO-Link?

IO-Link is a short-distance, bi-directional, digital, point-to-point, wired (or wireless) communication protocol. It’s designed for industrial environments to connect sensors and actuators to a control system, typically via an IO-Link Master. Think of it as a USB for industrial sensors and actuators, simplifying connections and unlocking advanced features.

Key characteristics include:

IO-Link System Components

A typical IO-Link system comprises:

1. IO-Link Master:
   • The gateway between IO-Link devices and higher-level automation systems (e.g., PLC, HMI, or an ESP32-based controller).
   • Manages communication with connected IO-Link devices.
   • Provides power to the IO-Link devices.
   • Can have one or more IO-Link ports.
   • In our context, the ESP32 will control an IO-Link Master PHY IC, which handles the actual IO-Link physical layer communication.
2. IO-Link Device:
   • A sensor (e.g., proximity, temperature, pressure) or an actuator (e.g., valve, gripper).
   • Contains an IODD (IO Device Description) file, which describes the device’s identity, parameters, process data, diagnostic information, and user interface structure.
3. Cables:
   • Standard unshielded 3-wire (for basic communication) or 5-wire (for additional functions/power) cables. M12 connectors are common.

graph TD
    subgraph Higher-Level Control
        A[<b>Automation System</b><br>e.g., PLC, HMI, or PC]
    end

    subgraph ESP32 Controller
        B(<b>ESP32 Host</b><br>Manages Logic & IODD)
    end

    subgraph IO-Link Master Hardware
        C{<b>IO-Link Master PHY</b><br>Handles 24V Signaling & Timing}
    end

    subgraph Field Level
        D1[IO-Link Sensor<br>e.g., Temperature]
        D2[IO-Link Sensor<br>e.g., Proximity]
        D3[IO-Link Actuator<br>e.g., Valve]
        D4[IO-Link Hub]
    end

    A -- "High-Level Commands" --> B
    B -- "UART / SPI Commands" --> C
    C -- "IO-Link Port 1" --> D1
    C -- "IO-Link Port 2" --> D2
    C -- "IO-Link Port 3" --> D3
    C -- "IO-Link Port 4" --> D4

    classDef default fill:#DBEAFE,stroke:#2563EB,stroke-width:1px,color:#1E40AF
    classDef startNode fill:#EDE9FE,stroke:#5B21B6,stroke-width:2px,color:#5B21B6
    classDef endNode fill:#D1FAE5,stroke:#059669,stroke-width:2px,color:#065F46
    classDef checkNode fill:#FEE2E2,stroke:#DC2626,stroke-width:1px,color:#991B1B

    class B,A startNode
    class D1,D2,D3,D4 endNode
    class C checkNode

IO-Link Communication Protocol

IO-Link communication is structured in layers:

1. Physical Layer (L1):
   • Defines electrical characteristics, connectors, and cables.
   • Signaling is typically 24V. The C/Q line is used for communication.
   • Supports different communication speeds (baud rates):
     • COM1: 4.8 kbit/s
     • COM2: 38.4 kbit/s
     • COM3: 230.4 kbit/s
   • The master initiates communication and detects the speed supported by the device.
2. Data Link Layer (L2):
   • Defines frame types and sequences for data exchange.
   • Uses M-sequences (Master Message Sequence) for communication cycles.
   • Frame types include:
     • Process Data (PD): Cyclically exchanged data (e.g., sensor readings, actuator setpoints).
     • On-request Data (OD) / Service Data (SDU): Acyclically exchanged data for parameterization, diagnostics, and identification. Also known as Index Service Data Unit (ISDU).
     • Events: Notifications from the device to the master (e.g., errors, warnings).
3. Application Layer (L3):
   • Defines the content and meaning of the data being exchanged.
   • This is where IODD files play a crucial role, providing a standardized way to interpret device data.

sequenceDiagram
    participant M as IO-Link Master (PHY)
    participant D as IO-Link Device

    M->>D: Wake-up Pulse
    activate D
    Note over M,D: Master initiates communication and discovers device capabilities.
    M->>D: Master Request (M-sequence)
    
    loop Cyclic Data Exchange
        M->>D: M-sequence Frame (contains Process Data Output - PDO)
        D-->>M: Device Response Frame (contains Process Data Input - PDI)
    end

    opt Acyclic Data Exchange (On-request)
        M->>D: M-sequence (Write Request: Index, Subindex, Data)
        D-->>M: Device Response (Acknowledgement)
        
        M->>D: M-sequence (Read Request: Index, Subindex)
        D-->>M: Device Response (Contains requested On-request Data)
    end

    opt Event Notification
        Note over D: Device detects an event (e.g., error, maintenance)
        D-->>M: Sets event flag in its response frame
        Note over M: Master detects event flag and requests details
        M->>D: M-sequence (Read Event Request)
        D-->>M: Device Response (Contains event details)
    end
    deactivate D

Data Types and IODD Files

• Process Data (PD):
  • Process Data Input (PDI): Data from the device to the master (e.g., sensor value).
  • Process Data Output (PDO): Data from the master to the device (e.g., actuator command).
  • Transmitted cyclically at the selected communication speed. The size can be up to 32 bytes.

• On-request Data (OD) / Service Data Unit (SDU):
  • Used for accessing device parameters, identification data (vendor, product ID), diagnostic information, etc.
  • Accessed acyclically using Index and Subindex addressing, similar to other fieldbus systems.
• IODD (IO Device Description):
  • An XML-based file that describes the IO-Link device. It’s like a “driver” file.
  • Contains information about:
    • Device identity (Vendor ID, Device ID, Product Name).
    • Communication properties.
    • Supported parameters (Index, Subindex, data type, range, default values).
    • Process data structure and content.
    • Diagnostic messages and events.
    • User interface elements (text, images for display in engineering tools).
  • The IO-Link Master (or the system controlling it) uses the IODD to understand how to communicate with and configure the device.

Operating Modes

An IO-Link port can operate in several modes:

• SIO (Standard Input/Output) Mode: The port behaves like a standard digital input or output. This allows legacy non-IO-Link devices to be connected.
• COM1, COM2, COM3 Modes: These are IO-Link communication modes corresponding to the baud rates mentioned earlier. The master and device negotiate the highest possible common speed during startup.
• Inactive: Port is disabled.

Benefits of IO-Link

• Standardization: Simplifies integration and reduces the variety of interfaces.
• Reduced Wiring: Uses standard 3-wire cables, minimizing wiring complexity and cost.
• Automated Parameterization: Allows for easy device replacement and setup by automatically downloading parameters to a new device.
• Extended Diagnostics: Provides detailed diagnostic information from the device level up to the control system.
• Increased Data Availability: Access to more data from sensors and actuators, enabling better process control and predictive maintenance.
• Remote Configuration: Devices can be configured remotely, reducing downtime.

ESP32 as an IO-Link Master Controller

Directly implementing the IO-Link physical layer (24V signaling, precise timing for COM1/2/3) on ESP32 GPIOs is highly challenging and generally not recommended. Instead, the ESP32 acts as a host controller for a dedicated IO-Link Master PHY IC (also known as an IO-Link transceiver or IO-Link master interface IC).

Examples of such PHY ICs include:

• STMicroelectronics L6360, L6362A
• Maxim Integrated (Analog Devices) MAX14819, MAX14827A
• Texas Instruments TIOF111, TIOF111A

The ESP32 communicates with this PHY IC, typically via UART or SPI. The PHY IC then handles:

• The 24V IO-Link physical layer signaling.
• The precise timing requirements for COM1, COM2, and COM3.
• Basic IO-Link frame assembly and disassembly.
• Short-circuit protection and other electrical robustness features.

The ESP32 is responsible for:

• Sending commands to the PHY to initiate IO-Link communication cycles.
• Configuring the PHY (e.g., setting the IO-Link port mode).
• Transmitting data (Process Data Outputs, On-request Data) to the PHY to be sent to the IO-Link device.
• Receiving data (Process Data Inputs, On-request Data responses, Events) from the PHY that originated from the IO-Link device.
• Managing the higher-level logic of the IO-Link communication (e.g., interpreting IODD information, application logic).

Practical Examples

This section will focus on the ESP32 communicating with an IO-Link Master PHY IC via UART. The actual IO-Link communication with the end device is handled by the PHY. The code examples will be conceptual, illustrating the principles, as the specific commands for the PHY will depend on the chosen IC’s datasheet.

Assumptions:

• You have an ESP32 development board.
• You have an IO-Link Master PHY IC evaluation board or a custom board with such an IC.
• You have an IO-Link compatible sensor or actuator.
• The IO-Link PHY IC communicates with the ESP32 via UART.

Hardware Setup

1. Connect ESP32 to IO-Link PHY IC:
   • Connect the ESP32’s UART TX pin to the PHY’s UART RX pin.
   • Connect the ESP32’s UART RX pin to the PHY’s UART TX pin.
   • Connect GND pins.
   • Provide necessary power to the ESP32 and the IO-Link PHY IC (the PHY will likely require its own power supply, often 24V for the IO-Link side).
   • Refer to the PHY IC’s datasheet for any additional control pins (e.g., reset, mode selection) that might need to be connected to ESP32 GPIOs.
2. Connect IO-Link Device to PHY IC:
   • Use a standard M12 (or M8/M5) IO-Link cable to connect your IO-Link device to an IO-Link port on the PHY IC’s board.

Software Setup

1. Create a new ESP-IDF Project:idf.py create-project io_link_master_example cd io_link_master_example
2. Configure the Project (if needed):Use idf.py menuconfig to adjust settings, particularly if you need to change default UART pins or configurations.

Code Snippet 1: Basic UART Configuration for IO-Link PHY Communication

This code initializes a UART interface that the ESP32 will use to send commands to and receive responses from the IO-Link Master PHY IC. The baud rate should match what the PHY IC expects for its control interface. This is not the IO-Link communication speed (COM1/2/3), which is handled by the PHY itself.

#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/uart.h"
#include "driver/gpio.h"
#include "esp_log.h"

static const char *TAG = "IO_LINK_MASTER";

// UART Configuration for communication with IO-Link PHY IC
#define PHY_UART_NUM            UART_NUM_2 // Example: Using UART2
#define PHY_UART_TXD_PIN        (GPIO_NUM_17)
#define PHY_UART_RXD_PIN        (GPIO_NUM_16)
#define PHY_UART_RTS_PIN        (UART_PIN_NO_CHANGE)
#define PHY_UART_CTS_PIN        (UART_PIN_NO_CHANGE)

#define PHY_UART_BAUD_RATE      115200 // Baud rate for ESP32 <-> PHY communication
#define PHY_UART_BUF_SIZE       1024

void init_phy_uart() {
    uart_config_t uart_config = {
        .baud_rate = PHY_UART_BAUD_RATE,
        .data_bits = UART_DATA_8_BITS,
        .parity    = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE,
        .source_clk = UART_SCLK_DEFAULT,
    };
    ESP_LOGI(TAG, "Configuring UART%d for IO-Link PHY communication...", PHY_UART_NUM);
    ESP_ERROR_CHECK(uart_driver_install(PHY_UART_NUM, PHY_UART_BUF_SIZE * 2, 0, 0, NULL, 0));
    ESP_ERROR_CHECK(uart_param_config(PHY_UART_NUM, &uart_config));
    ESP_ERROR_CHECK(uart_set_pin(PHY_UART_NUM, PHY_UART_TXD_PIN, PHY_UART_RXD_PIN, PHY_UART_RTS_PIN, PHY_UART_CTS_PIN));
    ESP_LOGI(TAG, "UART%d for PHY communication initialized.", PHY_UART_NUM);
}

void app_main(void) {
    init_phy_uart();
    ESP_LOGI(TAG, "IO-Link Master Controller Example Initialized.");
    // Further application logic will go here
}

Explanation:

• PHY_UART_NUM, PHY_UART_TXD_PIN, PHY_UART_RXD_PIN: Define which UART controller and pins are used. Adjust these based on your ESP32 variant and board layout.
• PHY_UART_BAUD_RATE: This baud rate is for communication between the ESP32 and the IO-Link Master PHY. It’s independent of the IO-Link communication speeds (COM1/2/3). Consult your PHY’s datasheet.
• uart_driver_install, uart_param_config, uart_set_pin: Standard ESP-IDF functions to configure and initialize the UART peripheral.

Code Snippet 2: Sending a Simple IO-Link Request (Conceptual)

This example demonstrates sending a command to the PHY to request identification data (e.g., Vendor ID, Device ID) from a connected IO-Link device. The actual command format (phy_command_buffer) is highly dependent on the specific IO-Link Master PHY IC you are using. You must consult its datasheet.

// ... (includes and defines from Snippet 1) ...

// Placeholder for PHY-specific command to read IO-Link device identification
// This is an EXAMPLE. Replace with actual commands from your PHY's datasheet.
// For instance, a command might involve:
// - Target IO-Link Port
// - IO-Link Index (e.g., 0x0010 for Vendor ID, 0x0011 for Device ID)
// - Subindex
// - Command type (read/write)
// - Expected response length

// Example: Hypothetical command to read Vendor ID (Index 16, Subindex 0) from port 0
// This format is purely illustrative.
const uint8_t cmd_read_vendor_id[] = {0x01, /* Port 0 */
                                      0x10, /* Command: Read On-request Data */
                                      0x00, 0x10, /* Index 16 (Vendor ID) */
                                      0x00, /* Subindex 0 */
                                      0x02  /* Expected data length (Vendor ID is 2 bytes) */
                                     }; 
// Checksum or other framing bytes might be needed by your PHY.

void send_phy_command(const uint8_t* command, size_t length) {
    int bytes_written = uart_write_bytes(PHY_UART_NUM, command, length);
    if (bytes_written == length) {
        ESP_LOGI(TAG, "Sent %d bytes to PHY: ", bytes_written);
        for(int i=0; i<length; i++) {
            printf("0x%02X ", command[i]);
        }
        printf("\n");
    } else {
        ESP_LOGE(TAG, "Error sending command to PHY, sent %d of %d bytes", bytes_written, length);
    }
}

// Returns number of bytes read, or -1 on error/timeout
int receive_phy_response(uint8_t* buffer, size_t buffer_size, int timeout_ms) {
    int bytes_read = uart_read_bytes(PHY_UART_NUM, buffer, buffer_size, pdMS_TO_TICKS(timeout_ms));
    if (bytes_read > 0) {
        ESP_LOGI(TAG, "Received %d bytes from PHY: ", bytes_read);
        for(int i=0; i<bytes_read; i++) {
            printf("0x%02X ", buffer[i]);
        }
        printf("\n");
    } else if (bytes_read == 0) {
        ESP_LOGI(TAG, "Timeout waiting for PHY response.");
    } else {
        ESP_LOGE(TAG, "UART read error from PHY.");
    }
    return bytes_read;
}

void request_device_identification_task(void *pvParameters) {
    uint8_t response_buffer[32]; // Adjust size as needed for expected responses

    vTaskDelay(pdMS_TO_TICKS(2000)); // Wait for PHY to be ready

    ESP_LOGI(TAG, "Requesting Vendor ID from IO-Link device...");
    send_phy_command(cmd_read_vendor_id, sizeof(cmd_read_vendor_id));
    
    int len = receive_phy_response(response_buffer, sizeof(response_buffer), 1000);

    if (len > 0) { // Assuming response contains the Vendor ID directly after some status bytes
        // Parse response_buffer according to your PHY's datasheet
        // Example: if PHY returns [Status, Length, Byte1, Byte2] for Vendor ID
        if (len >= 4 && response_buffer[0] == 0x00 /* hypothetical success status */) {
            uint16_t vendor_id = (response_buffer[2] << 8) | response_buffer[3];
            ESP_LOGI(TAG, "Received Vendor ID: 0x%04X", vendor_id);
        } else {
            ESP_LOGW(TAG, "PHY response indicates error or unexpected format for Vendor ID.");
        }
    }
    vTaskDelete(NULL);
}


void app_main(void) {
    init_phy_uart();
    ESP_LOGI(TAG, "IO-Link Master Controller Example Initialized.");

    xTaskCreate(request_device_identification_task, "req_dev_id_task", 4096, NULL, 5, NULL);
}

Explanation:

• cmd_read_vendor_id: This is a placeholder. You MUST replace this with the actual byte sequence required by your IO-Link Master PHY IC to read the Vendor ID (typically Index 16, Subindex 0) from an IO-Link device.
• send_phy_command(): A simple function to send a command buffer via UART.
• receive_phy_response(): A function to read the response from the PHY with a timeout.
• request_device_identification_task(): A FreeRTOS task that sends the command and attempts to parse the response.
• Response Parsing: The way you parse response_buffer is critical and entirely dependent on your PHY’s communication protocol. The PHY might add its own status bytes, length indicators, or checksums to the IO-Link data.

Tip: Many IO-Link Master PHY ICs have evaluation kits that come with example code for a host microcontroller (though perhaps not ESP32 directly). This code can be an invaluable resource for understanding the PHY’s command set.

Code Snippet 3: Reading Process Data (Conceptual)

Process data is typically read cyclically. The PHY might have a mode where it automatically polls the IO-Link device and makes the latest process data available, or you might need to send a specific command to request it.

// ... (includes and defines from Snippet 1) ...
// ... (send_phy_command and receive_phy_response functions) ...

// Placeholder for PHY-specific command to read Process Data Input (PDI)
// This is an EXAMPLE. Replace with actual commands from your PHY's datasheet.
// For instance, a command might involve:
// - Target IO-Link Port
// - Command type (read PDI)
// - Expected PDI length (from IODD or device configuration)
const uint8_t cmd_read_pdi[] = {0x01, /* Port 0 */
                                0x20, /* Command: Read Process Data Input */
                                0x04  /* Expected PDI length (e.g., 4 bytes) */
                               };
// Checksum or other framing bytes might be needed by your PHY.

void read_process_data_task(void *pvParameters) {
    uint8_t pdi_buffer[32]; // Adjust size for max expected PDI

    while(1) {
        vTaskDelay(pdMS_TO_TICKS(100)); // Read PDI every 100ms (adjust as needed)

        ESP_LOGD(TAG, "Requesting Process Data Input (PDI)...");
        send_phy_command(cmd_read_pdi, sizeof(cmd_read_pdi));
        
        int len = receive_phy_response(pdi_buffer, sizeof(pdi_buffer), 50); // Shorter timeout for cyclic data

        if (len > 0) {
            // Parse pdi_buffer according to your PHY's datasheet and device's IODD
            // Example: if PHY returns [Status, Length, PDI_Byte1, PDI_Byte2, ...]
            if (pdi_buffer[0] == 0x00 /* hypothetical success status */ && len >= (2 + cmd_read_pdi[2]) ) {
                ESP_LOGI(TAG, "Received PDI (length %d): ", cmd_read_pdi[2]);
                for(int i=0; i < cmd_read_pdi[2]; i++) {
                    printf("0x%02X ", pdi_buffer[i+2]); // Assuming PDI starts after status and length bytes
                }
                printf("\n");
                // Further processing of PDI based on IODD (e.g., converting to temperature, pressure)
            } else {
                ESP_LOGW(TAG, "PHY response indicates error or unexpected format for PDI.");
            }
        }
    }
}

void app_main(void) {
    init_phy_uart();
    ESP_LOGI(TAG, "IO-Link Master Controller Example Initialized.");

    // xTaskCreate(request_device_identification_task, "req_dev_id_task", 4096, NULL, 5, NULL);
    xTaskCreate(read_process_data_task, "read_pdi_task", 4096, NULL, 5, NULL);
}

Explanation:

• cmd_read_pdi: Another placeholder command. Consult your PHY’s datasheet. The expected PDI length often comes from the IODD file of the connected IO-Link device.
• read_process_data_task(): This task periodically sends the command to read PDI and processes the response.
• The polling interval (vTaskDelay) should be chosen based on application requirements and the IO-Link cycle time.

Build Instructions

1. Save your code (e.g., in main/io_link_master_example_main.c).
2. Open the ESP-IDF Terminal in VS Code.
3. Build the project:idf.py build

Run/Flash/Observe Steps

1. Connect your ESP32 board to your computer.
2. Flash the firmware:idf.py -p (Your_ESP32_Serial_Port) flash
Replace (Your_ESP32_Serial_Port) with the actual port (e.g., /dev/ttyUSB0 or COM3).
3. Monitor the output:idf.py -p (Your_ESP32_Serial_Port) monitor
4. Observe:
   • You should see log messages from the ESP32 indicating UART initialization.
   • If your PHY commands and parsing logic are correct, you should see logs showing commands sent to the PHY and responses received.
   • With an IO-Link device connected and correctly configured PHY commands, you might see actual data like Vendor ID or Process Data values.
   • If there are issues, you’ll likely see error messages or timeouts.

Warning: The provided code snippets are conceptual. The success of communication heavily relies on using the correct command sequences and response parsing logic specific to your chosen IO-Link Master PHY IC. Always refer to the IC’s datasheet as your primary guide.

Variant Notes

The core logic of communicating with an IO-Link Master PHY via UART is largely consistent across ESP32 variants. However, some differences might arise:

• ESP32: Has 3 UART controllers. Sufficient GPIOs.
• ESP32-S2: Has 2 UART controllers. Ensure the chosen UART pins don’t conflict with other peripherals (e.g., USB OTG if used).
• ESP32-S3: Has 3 UART controllers. Ample GPIOs. Similar considerations as ESP32.
• ESP32-C3: Has 2 UART controllers. Fewer GPIOs overall, so pin selection needs care.
• ESP32-C6: Has 2 UART controllers. RISC-V core with Wi-Fi 6 and Bluetooth 5.3. UART functionality for this purpose is similar to C3.
• ESP32-H2: Has 2 UART controllers. Primarily focused on Thread/Zigbee/BLE. UART functionality is standard.

Key Considerations for All Variants:

1. UART Availability: All listed variants have at least two UART controllers, which is generally sufficient for debugging (UART0) and PHY communication (UART1 or UART2).
2. GPIO Mapping: Ensure the GPIOs selected for UART TXD and RXD are correctly configured and not multiplexed for other critical functions. Refer to the specific variant’s datasheet for pinout options and IO MUX details.
3. Processing Power: Interfacing with a PHY via UART and managing IO-Link data is well within the capabilities of all these ESP32 variants. The PHY offloads the most timing-critical parts of the IO-Link protocol.
4. Power Requirements: Remember that the IO-Link PHY and the connected IO-Link devices typically operate at 24V. The ESP32 itself operates at 3.3V. Proper power domain separation and level shifting (if the PHY’s UART interface isn’t 3.3V tolerant) are crucial. Most modern PHYs will have 3.3V compatible logic lines for UART.

The choice of ESP32 variant will likely be driven more by other system requirements (e.g., Wi-Fi/Bluetooth needs, number of other peripherals, cost) rather than specific limitations related to IO-Link master PHY control via UART.

Common Mistakes & Troubleshooting Tips

Exercises

1. Research an IO-Link Master PHY IC:
   • Select one IO-Link Master PHY IC (e.g., MAX14827A, L6362A, TIOF111).
   • Find its datasheet.
   • List its key features relevant to an ESP32 interface (e.g., UART/SPI control, number of IO-Link channels, supported COM speeds).
   • Identify the basic UART commands for:
     • Initializing a port.
     • Reading the Vendor ID (Index 16) from a connected device.
     • Reading current process data.
2. Conceptual Command Implementation:
   • Based on the PHY IC researched in Exercise 1, write down the exact byte sequences (as C arrays) for the cmd_read_vendor_id and cmd_read_pdi placeholders used in the chapter’s code snippets. Explain each byte’s meaning.
3. Periodic Process Data Polling with Error Indication:
   • Modify the read_process_data_task from Code Snippet 3.
   • If receive_phy_response indicates a timeout or an error status from the PHY, increment an error counter.
   • Log a warning message if the error counter exceeds a certain threshold (e.g., 3 consecutive errors).
   • Reset the error counter upon a successful read.
4. Basic IODD Interpretation (Conceptual):
   • Assume an IO-Link temperature sensor provides its reading as a 16-bit signed integer in 0.1 °C resolution as part of its Process Data Input (PDI). The PDI also includes a status byte.
   • If the PDI received from the PHY (after stripping PHY-specific framing) is [Status_Byte, Temp_MSB, Temp_LSB], write a C function that takes this 3-byte PDI array, extracts the temperature, converts it to a floating-point value in °C, and prints it. Also, print a message if the Status_Byte indicates an error (e.g., if Status_Byte != 0).

Summary

• IO-Link is a standardized point-to-point communication protocol for smart sensors and actuators in industrial automation.
• It enables bi-directional communication for process data, configuration parameters, and diagnostics.
• An IO-Link system consists of an IO-Link Master, IO-Link Devices, and standard cables.
• IODD files are crucial for describing device capabilities and data structures.
• The ESP32 can act as a host controller for an IO-Link Master PHY IC, communicating typically via UART or SPI.
• The PHY IC handles the 24V IO-Link physical layer and timing-critical aspects of COM1, COM2, and COM3 speeds.
• ESP-IDF’s UART driver is used to send commands to the PHY and receive responses.
• Command sets and response formats are specific to the chosen PHY IC and must be obtained from its datasheet.
• All common ESP32 variants (ESP32, S2, S3, C3, C6, H2) are capable of controlling an IO-Link PHY via UART.
• Careful attention to wiring, baud rates, PHY command syntax, and power supplies is essential for successful implementation.

Further Reading

• IO-Link Consortium Official Website: https://io-link.com/ (Specifications, IODD Finder, technology basics)
• ESP-IDF API Reference – UART: https://docs.espressif.com/projects/esp-idf/en/v5.4/esp32/api-reference/peripherals/uart.html (Replace esp32 with your target variant if needed, e.g., esp32s3)
• Datasheets for IO-Link Master PHY ICs:
  • Analog Devices (Maxim Integrated): Search for MAX14819, MAX14827A, etc. on https://www.analog.com/
  • STMicroelectronics: Search for L6360, L6362A, etc. on https://www.st.com/
  • Texas Instruments: Search for TIOF111, etc. on https://www.ti.com/
• Application Notes from PHY IC Manufacturers: These often provide detailed guidance on interfacing their PHYs with microcontrollers and implementing IO-Link communication.