Chapter 168: Parallel IO (ParIO) Interface

Chapter Objectives

After completing this chapter, you will be able to:

• Understand the concept of Parallel I/O (ParIO) and its advantages for high-speed data transfer.
• Identify ESP32 variants that support dedicated high-speed parallel interfaces.
• Learn about the architecture of typical parallel interfaces like the Intel 8080 bus.
• Configure and use a parallel IO interface (specifically an 8080-like interface for an LCD) using ESP-IDF v5.x.
• Understand the role of control signals (CS, WR, RD, D/C) in parallel communication.
• Recognize common issues and troubleshoot ParIO implementations.

Introduction

In the world of embedded systems, data needs to be exchanged between the microcontroller and various peripherals such as displays, cameras, and high-speed ADCs/DACs. While serial interfaces like SPI and I2C are common and use fewer pins, they can become a bottleneck when high data throughput is required. This is where Parallel I/O (ParIO) interfaces shine.

Parallel I/O transmits multiple bits of data simultaneously over multiple data lines, significantly increasing the data transfer rate compared to serial methods. This chapter explores the fundamentals of ParIO, its relevance in modern ESP32 applications, and how to utilize the parallel interface capabilities provided by newer ESP32 variants, particularly focusing on the common Intel 8080-style interface often used for LCD controllers. While ESP-IDF might not have a single generic driver named “ParIO” for all purposes, it provides drivers for specific parallel peripherals like LCD controllers that leverage these underlying parallel bus capabilities.

Theory

What is Parallel I/O?

A parallel interface is a method of sending multiple binary digits (bits) of data simultaneously using multiple wires. If an interface has 8 data lines, it can transmit 8 bits (one byte) in a single clock cycle or control signal pulse. This is in contrast to serial interfaces (like UART, SPI, I2C) which send data one bit at a time over a single data line (or a pair).

Key Characteristics of Parallel Interfaces:

• High Speed: The primary advantage. By transmitting multiple bits at once, data throughput can be significantly higher than serial interfaces operating at similar clock speeds.
• More Pins: Requires more GPIO pins for the data lines (e.g., 8, 16, or more) plus several control lines. This can be a constraint on pin-limited MCUs.
• Shorter Distances: Due to issues like clock skew (slight differences in arrival times of bits on parallel lines) and noise, parallel interfaces are typically used for short-distance communication, often within the same PCB.
• Synchronous or Asynchronous:
  • Synchronous: A dedicated clock signal times the data transfer.
  • Asynchronous: Control signals (like Write Enable, Read Enable) manage the data flow without a continuous clock for each data bit. The Intel 8080 interface is an example of an asynchronous parallel bus.

Common Parallel Interface Standards

One of the most common parallel interface standards encountered with embedded peripherals, especially character and graphic LCDs, is the Intel 8080 interface (also known as i80 or MCS-80 bus). Another similar standard is the Motorola 6800 interface.

Intel 8080 Interface Signals:

The 8080 interface typically uses the following signals:

• Data Lines (D0-D7, D0-D15, etc.): Bidirectional lines used to transfer data. Common widths are 8-bit and 16-bit.
• Chip Select (/CS or CS): Active low signal. Selects the peripheral to communicate with.
• Write Enable (/WR or WR): Active low signal. The MCU pulses this line low to indicate that it is writing data to the peripheral. Data should be stable on the data lines when /WR goes high (rising edge often latches data).
• Read Enable (/RD or RD): Active low signal. The MCU pulses this line low to indicate that it is reading data from the peripheral. Data becomes available from the peripheral while /RD is low.
• Data/Command (D/C or RS – Register Select): This signal tells the peripheral whether the data on the bus is a command (e.g., instruction to clear display) or actual data (e.g., pixel data or character codes).
  • D/C = Low: Command
  • D/C = High: Data
• Reset (/RESET or RES): Active low signal. Used to reset the peripheral to a known state. (Optional, sometimes handled by software).

ESP32 Parallel Interface Capabilities

Newer ESP32 variants, particularly the ESP32-S2, ESP32-S3, ESP32-C6, and ESP32-H2, include dedicated hardware support for parallel interfaces, often integrated into a peripheral block commonly referred to as the “LCD_CAM” interface. This hardware can be configured to drive parallel LCDs (e.g., using 8080, RGB interfaces) or receive data from parallel cameras.

The ESP-IDF provides drivers, such as esp_lcd, to configure and manage these parallel buses. For an 8080-style interface, the esp_lcd_panel_io_i80 component is used. This driver handles the low-level signal timing and data transfer, often utilizing DMA (Direct Memory Access) for efficient, high-speed operations without continuous CPU intervention.

DMA (Direct Memory Access):

DMA is crucial for high-speed parallel interfaces. It allows the peripheral (in this case, the ESP32’s parallel interface controller) to transfer data directly to or from memory without involving the CPU for every byte or word. The CPU sets up the DMA transfer (source address, destination address, data length) and then the DMA controller takes over, freeing up the CPU for other tasks. This is essential for achieving high frame rates on displays or capturing high-resolution camera data.

sequenceDiagram
    participant CPU
    participant DMA_Controller
    participant Memory_RAM
    participant ParIO_Hardware

    %% --- Without DMA ---
    Note over CPU,ParIO_Hardware: Without DMA

    CPU->>Memory_RAM: 1. Read byte from Memory
    CPU->>ParIO_Hardware: 2. Write byte to ParIO
    Note over CPU,ParIO_Hardware: CPU is busy for every single byte.<br>Repeats for all data.

    %% --- With DMA ---
    Note over CPU,DMA_Controller: With DMA

    CPU->>DMA_Controller: 1. Setup Transfer<br>(Source, Dest, Length)
    CPU-->>CPU: 2. Go do other tasks...

    activate DMA_Controller
    DMA_Controller->>Memory_RAM: 3. Read data block
    Memory_RAM-->>DMA_Controller: Data
    DMA_Controller->>ParIO_Hardware: 4. Transfer data block directly
    deactivate DMA_Controller

    ParIO_Hardware->>DMA_Controller: 5. Transfer Complete
    DMA_Controller->>CPU: 6. (Optional) Interrupt CPU

Practical Examples

Let’s demonstrate how to configure and use an 8-bit Intel 8080 parallel interface to send data, simulating communication with a parallel LCD. We will use the esp_lcd driver available in ESP-IDF v5.x. This example will focus on the ESP32-S3 due to its robust LCD_CAM peripheral.

Scenario: We will configure an 8-bit parallel output (simulating an 8080 interface) and send a sequence of commands and data. To observe the output, you would typically connect these pins to a logic analyzer or an actual 8080-compatible LCD.

Prerequisites:

1. ESP32-S3 development board.
2. ESP-IDF v5.x installed and configured with VS Code.
3. Logic analyzer (optional, but highly recommended for observing signals).

1. Project Setup

Create a new ESP-IDF project in VS Code or use an existing one.

2. main/CMakeLists.txt

Ensure your CMakeLists.txt includes the necessary components:

idf_component_register(SRCS "main.c"
                    INCLUDE_DIRS "."
                    REQUIRES driver esp_lcd esp_rom esp_log)

• driver: For GPIO control.
• esp_lcd: The LCD peripheral driver which includes 8080 support.
• esp_rom: For esp_rom_gpio_connect_out_signal.
• esp_log: For logging.

3. main/main.c

#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/gpio.h"
#include "esp_lcd_panel_io.h"
#include "esp_lcd_panel_ops.h"
#include "esp_log.h"
#include "soc/soc_caps.h" // For SOC_LCD_I80_SUPPORTED
#include "esp_rom_gpio.h" // For esp_rom_gpio_connect_out_signal

static const char *TAG = "pario_example";

// Define GPIOs for the 8080 interface
// These pins are just examples; choose appropriate pins for your ESP32-S3 board
// Consult your ESP32-S3 datasheet for suitable GPIOs for LCD/Camera functions
#define EXAMPLE_LCD_I80_CS_PIN      GPIO_NUM_9
#define EXAMPLE_LCD_I80_WR_PIN      GPIO_NUM_10
#define EXAMPLE_LCD_I80_DC_PIN      GPIO_NUM_11
// Data pins D0-D7
#define EXAMPLE_LCD_I80_D0_PIN      GPIO_NUM_1
#define EXAMPLE_LCD_I80_D1_PIN      GPIO_NUM_2
#define EXAMPLE_LCD_I80_D2_PIN      GPIO_NUM_3
#define EXAMPLE_LCD_I80_D3_PIN      GPIO_NUM_4
#define EXAMPLE_LCD_I80_D4_PIN      GPIO_NUM_5
#define EXAMPLE_LCD_I80_D5_PIN      GPIO_NUM_6
#define EXAMPLE_LCD_I80_D6_PIN      GPIO_NUM_7
#define EXAMPLE_LCD_I80_D7_PIN      GPIO_NUM_8

#define EXAMPLE_LCD_PIXEL_CLOCK_HZ (2 * 1000 * 1000) // 2 MHz PCLK
#define EXAMPLE_LCD_CMD_BITS       8 // Command bit width
#define EXAMPLE_LCD_PARAM_BITS     8 // Parameter bit width

// Simple function to send a command
static void panel_io_send_command(esp_lcd_panel_io_handle_t io, uint8_t cmd) {
    esp_lcd_panel_io_tx_param(io, cmd, NULL, 0);
    ESP_LOGI(TAG, "Sent command: 0x%02X", cmd);
}

// Simple function to send data (single byte)
static void panel_io_send_data_byte(esp_lcd_panel_io_handle_t io, uint8_t data) {
    esp_lcd_panel_io_tx_param(io, data, NULL, 0); // For 8080, data is also sent via tx_param if DC is high
                                                // A more direct way for larger data buffers is tx_color
    ESP_LOGI(TAG, "Sent data byte: 0x%02X", data);
}

// Simple function to send a buffer of data
static void panel_io_send_data_buffer(esp_lcd_panel_io_handle_t io, const uint8_t *data, size_t len) {
    esp_lcd_panel_io_tx_color(io, -1, data, len); // -1 for cmd means use D/C line as per config
    ESP_LOGI(TAG, "Sent data buffer of length: %d", len);
}


void app_main(void) {
    ESP_LOGI(TAG, "Initialize Intel 8080 Parallel IO");

#if SOC_LCD_I80_SUPPORTED
    ESP_LOGI(TAG, "SoC supports I80 interface");

    esp_lcd_i80_bus_handle_t i80_bus = NULL;
    esp_lcd_i80_bus_config_t bus_config = {
        .dc_gpio_num = EXAMPLE_LCD_I80_DC_PIN,
        .wr_gpio_num = EXAMPLE_LCD_I80_WR_PIN,
        .clk_src = LCD_CLK_SRC_DEFAULT, // Use default clock source (e.g. PLL_D2_CLK)
        .data_gpio_nums = {
            EXAMPLE_LCD_I80_D0_PIN,
            EXAMPLE_LCD_I80_D1_PIN,
            EXAMPLE_LCD_I80_D2_PIN,
            EXAMPLE_LCD_I80_D3_PIN,
            EXAMPLE_LCD_I80_D4_PIN,
            EXAMPLE_LCD_I80_D5_PIN,
            EXAMPLE_LCD_I80_D6_PIN,
            EXAMPLE_LCD_I80_D7_PIN,
        },
        .bus_width = 8, // 8-bit data bus
        .max_transfer_bytes = 1024, // Max buffer size for one transaction
        .psram_trans_align = 0, // No specific PSRAM alignment needed for this example
        .sram_trans_align = 4    // ESP32-S3 DMA requires 4-byte alignment for SRAM
    };
    ESP_ERROR_CHECK(esp_lcd_new_i80_bus(&bus_config, &i80_bus));
    ESP_LOGI(TAG, "I80 bus created");

    esp_lcd_panel_io_handle_t io_handle = NULL;
    esp_lcd_panel_io_i80_config_t io_config = {
        .cs_gpio_num = EXAMPLE_LCD_I80_CS_PIN,
        .pclk_hz = EXAMPLE_LCD_PIXEL_CLOCK_HZ,
        .trans_queue_depth = 10, // Transaction queue size
        .dc_levels = {
            .dc_idle_level = 0, // D/C line idle level (can be 0 or 1)
            .dc_cmd_level = 0,  // D/C line level for command
            .dc_dummy_level = 0,// D/C line level for dummy phase (not used in this example)
            .dc_data_level = 1, // D/C line level for data/parameters
        },
        .flags = {
            .cs_active_high = 0,    // CS is active low
            .reverse_color_bits = 0,// No bit order reversal
            .swap_color_bytes = 0,  // No byte swapping for 8-bit interface
            .pclk_active_neg = 0,   // PCLK active on positive edge (WR signal for 8080)
            .pclk_idle_high = 1,    // PCLK (WR signal) idle high for 8080
        },
        .on_color_trans_done = NULL, // No callback needed for this example
        .user_ctx = NULL,
        .lcd_cmd_bits = EXAMPLE_LCD_CMD_BITS,
        .lcd_param_bits = EXAMPLE_LCD_PARAM_BITS,
    };
    ESP_ERROR_CHECK(esp_lcd_new_panel_io_i80(i80_bus, &io_config, &io_handle));
    ESP_LOGI(TAG, "I80 panel IO created");

    // --- Example: Sending commands and data ---
    // This simulates initializing an LCD or sending data to a parallel peripheral

    // Send a "Software Reset" command (example command)
    panel_io_send_command(io_handle, 0x01);
    vTaskDelay(pdMS_TO_TICKS(120)); // Delay after reset

    // Send "Display On" command (example command)
    panel_io_send_command(io_handle, 0x29);
    vTaskDelay(pdMS_TO_TICKS(20));

    // Send some data (e.g., pixel data or character codes)
    // For an actual LCD, you'd set column/page addresses first
    // Here, we just send a pattern
    uint8_t data_pattern[] = {0xAA, 0x55, 0xFF, 0x00, 0x12, 0x34, 0x56, 0x78};

    // Method 1: Sending data bytes one by one (less efficient for large data)
    // This uses tx_param, which internally sets D/C high before sending.
    // For this to work as "data", the dc_data_level must be configured correctly,
    // and the command value passed to tx_param is actually the data byte.
    // This is a bit of a quirk for 8080 where commands and single-byte params use the same path.
    // For actual data transmission, tx_color is preferred.
    // ESP_LOGI(TAG, "Sending data bytes one by one (using tx_param with D/C high):");
    // for (int i = 0; i < sizeof(data_pattern); i++) {
    //    panel_io_send_data_byte(io_handle, data_pattern[i]); // This will use D/C high
    //    vTaskDelay(pdMS_TO_TICKS(1)); // Small delay for observation
    // }

    // Method 2: Sending a buffer of data (more efficient)
    // This uses tx_color. The first parameter (-1) tells it to use D/C as data.
    ESP_LOGI(TAG, "Sending data buffer (using tx_color):");
    panel_io_send_data_buffer(io_handle, data_pattern, sizeof(data_pattern));
    vTaskDelay(pdMS_TO_TICKS(100)); // Delay for observation

    ESP_LOGI(TAG, "Example finished. Idling...");

    // In a real application, you might delete the bus and IO handle when done
    // esp_lcd_panel_io_del(io_handle);
    // esp_lcd_del_i80_bus(i80_bus);

#else
    ESP_LOGE(TAG, "SoC does not support I80 interface for this example.");
#endif // SOC_LCD_I80_SUPPORTED

    while (1) {
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

Explanation of main.c:

flowchart TD


    A[Start app_main] --> B{SoC Supports<br>I80 Interface?};
    B -- No --> B_NO[Log Error & End];

    B -- Yes --> C[Define bus_config Struct];
    C --> D["Populate bus_config:<br>- DC/WR GPIOs<br>- Data GPIO array<br>- Bus width (8)<br>- Max transfer bytes"];
    D --> E(esp_lcd_new_i80_bus);
    E --> F{Bus Created<br>Successfully?};
    F -- No --> F_NO(Handle Error);
    F -- Yes --> G[Define io_config Struct];
    G --> H["Populate io_config:<br>- CS GPIO<br>- PCLK Speed<br>- DC Logic Levels<br>- Signal Polarity Flags"];
    H --> I(esp_lcd_new_panel_io_i80);
    I --> J{Panel IO Created<br>Successfully?};
    J -- No --> J_NO(Handle Error);
    J -- Yes --> K[Send Commands & Data<br>using io_handle];
    K --> L[Program enters<br>idle loop];
    L --> Z[End];


    classDef start-end-node fill:#EDE9FE,stroke:#5B21B6,stroke-width:2px,color:#5B21B6;
    classDef process-node fill:#DBEAFE,stroke:#2563EB,stroke-width:1px,color:#1E40AF;
    classDef decision-node fill:#FEF3C7,stroke:#D97706,stroke-width:1px,color:#92400E;
    classDef check-node fill:#FEE2E2,stroke:#DC2626,stroke-width:1px,color:#991B1B;

    class A,Z start-end-node;
    class C,D,G,H,K,L,E,I,B_NO,F_NO,J_NO process-node;
    class B,F,J decision-node;

1. Includes: Necessary headers for FreeRTOS, GPIO, esp_lcd components, logging, and SoC capabilities.
2. GPIO Definitions: Defines the GPIO pins used for CS, WR, D/C, and the 8 data lines (D0-D7). Important: You must choose pins that are available on your specific ESP32-S3 board and are suitable for high-speed peripheral functions. Refer to your board’s schematic and the ESP32-S3 datasheet.
3. Configuration:
   • esp_lcd_i80_bus_config_t: Configures the 8080 bus itself.
     • dc_gpio_num, wr_gpio_num: Assigns D/C and WR signal pins.
     • clk_src: Clock source for the LCD peripheral. LCD_CLK_SRC_DEFAULT is usually fine.
     • data_gpio_nums: Array of GPIOs for the data bus.
     • bus_width: Set to 8 for an 8-bit parallel interface.
     • max_transfer_bytes: Maximum data size in a single DMA transaction. This influences internal buffer sizes.
     • sram_trans_align: DMA alignment requirement for SRAM. ESP32-S3 DMA often requires 4-byte alignment.
   • esp_lcd_panel_io_i80_config_t: Configures the I/O operations on the bus for a specific panel.
     • cs_gpio_num: Chip select pin.
     • pclk_hz: The effective clock frequency for the parallel data transfer (related to WR pulse rate).
     • trans_queue_depth: How many transactions can be queued.
     • dc_levels: Defines the GPIO logic levels for D/C in idle, command, and data states. Crucial for correct 8080 operation.
     • flags: Various flags to control signal polarity and data handling (e.g., cs_active_high, pclk_idle_high). For 8080, /WR is typically active low and idles high, so pclk_idle_high = 1 and pclk_active_neg = 0 (as PCLK here represents the WR signal’s behavior).
     • lcd_cmd_bits, lcd_param_bits: Bit width of commands and parameters (usually 8 for 8080).
4. Initialization:
   • esp_lcd_new_i80_bus(): Creates a new 8080 bus instance.
   • esp_lcd_new_panel_io_i80(): Creates a panel I/O handle associated with the bus. This io_handle is then used for transactions.
5. Sending Commands and Data:
   • esp_lcd_panel_io_tx_param(io_handle, cmd_value, param_buffer, param_size): This function is versatile.
     • To send a command: cmd_value is the command byte, param_buffer is NULL, param_size is 0. The D/C line will be set to dc_cmd_level.
     • To send parameters for a command (or small data with D/C high): cmd_value is the parameter byte (if lcd_param_bits matches lcd_cmd_bits), param_buffer is NULL, param_size is 0. The D/C line will be set to dc_data_level.
   • esp_lcd_panel_io_tx_color(io_handle, cmd_value, color_buffer, color_size): This function is primarily for sending larger blocks of data (like pixel color data).
     • If cmd_value is non-negative, it’s treated as a command sent first (D/C low), followed by the color_buffer (D/C high).
     • If cmd_value is -1 (or any negative value), it indicates that no command should be prefixed, and the color_buffer is sent directly with the D/C line set to dc_data_level. This is the typical way to send pixel data.
6. Helper Functions: panel_io_send_command, panel_io_send_data_byte, and panel_io_send_data_buffer are simple wrappers to illustrate usage.

4. Build, Flash, and Observe

1. Connect Logic Analyzer (Optional):
   • Connect your logic analyzer probes to the ESP32-S3 pins defined for CS, WR, D/C, and D0-D7.
   • Set up your logic analyzer to trigger on the CS signal or WR signal and capture these lines.
2. Build the Project:
   • Open a new ESP-IDF terminal in VS Code (Terminal -> New Terminal, then click the ESP-IDF icon in the status bar or run idf.py terminal if not automatically activated).
   • Run idf.py build.
3. Flash the Project:
   • Connect your ESP32-S3 board.
   • Run idf.py -p (PORT) flash monitor (replace (PORT) with your ESP32’s serial port, e.g., COM3 or /dev/ttyUSB0).
4. Observe:
   • Serial Monitor: You should see log messages indicating commands and data being “sent.”
   • Logic Analyzer: You will see the actual waveforms on the GPIO pins.
     • Verify the CS line goes active (low) during transactions.
     • Observe the D/C line: low for commands, high for data.
     • Observe the WR line: pulsing low for each byte written. Data on D0-D7 should be stable when WR transitions from low to high.
     • Check the data lines D0-D7 to see the values 0x01, 0x29, and the data_pattern being transmitted.

Tip: The pclk_hz in esp_lcd_panel_io_i80_config_t determines the speed of the WR strobes. If your peripheral is slow, you might need to reduce this frequency. The actual WR pulse width and setup/hold times are derived from this PCLK and internal bus timings.

Variant Notes

• ESP32-S3, ESP32-C6, ESP32-H2: These variants have a dedicated LCD_CAM peripheral that provides robust support for parallel interfaces like 8080, 6800, and parallel RGB for LCDs, and parallel camera interfaces. The esp_lcd driver (specifically esp_lcd_panel_io_i80) is the primary way to use these for 8080-style communication. DMA support is integral.
• ESP32-S2: Also features an LCD_CAM peripheral with similar capabilities to the ESP32-S3, supporting parallel LCD and camera interfaces. The esp_lcd driver is applicable here as well.
• ESP32 (Original): Does not have a dedicated LCD_CAM peripheral like the S2/S3/C6/H2. However, its I2S peripheral can be configured in “parallel mode” (LCD mode) to drive parallel displays. This is more complex to configure for a generic 8080 interface as it’s primarily designed for continuous data streaming (like for an ST7789 display without its own GRAM). It involves setting up I2S in parallel, managing DMA descriptors, and manually controlling signals like D/C if not directly supported by the I2S LCD mode for that specific signal. For general 8080, bit-banging with careful timing or using SPI with shift registers might be considered, but these are not true “ParIO” in the high-speed hardware sense.
• ESP32-C3: This is a RISC-V variant with a focus on low cost and connectivity. It does not have a dedicated high-speed parallel LCD_CAM interface. Parallel I/O would typically be limited to bit-banging GPIOs (slow) or using its SPI peripheral creatively if the target device can accommodate it (e.g., SPI-to-parallel shift registers). True high-speed parallel interfaces are not a primary feature.

Conclusion on Variants: For high-speed, DMA-assisted parallel I/O targeting peripherals like LCDs or cameras using interfaces like 8080, the ESP32-S2, ESP32-S3, ESP32-C6, and ESP32-H2 are the most suitable choices due to their dedicated LCD_CAM hardware and corresponding ESP-IDF driver support (esp_lcd).

Common Mistakes & Troubleshooting Tips

Exercises

1. Modify Pin Configuration: Change the GPIO pin assignments in the example code to a different set of available pins on your ESP32-S3 board. Recompile, flash, and verify with a logic analyzer that the signals appear on the new pins.
2. Implement a Read Operation (Conceptual): The esp_lcd_panel_io_i80 interface is primarily optimized for TX (writing to displays). Reading back from an 8080 device typically requires configuring data lines as inputs and managing the /RD signal. Research how you might (even if only conceptually or by bit-banging for this exercise, as esp_lcd focuses on TX) read a status register from a hypothetical 8080 peripheral. What control signals would you need to manipulate?
   • Hint: This would involve setting data GPIOs to input mode, asserting CS, setting D/C appropriately, pulsing RD low, and then reading the data lines. The esp_lcd driver may not directly support this for generic reads, so consider how it would be done at a lower GPIO level if needed.
3. 16-bit Data Bus Simulation: Modify the example to simulate a 16-bit data bus (D0-D15).
   • Change bus_config.bus_width to 16.
   • Expand bus_config.data_gpio_nums to include 16 data pins.
   • Adjust EXAMPLE_LCD_CMD_BITS and EXAMPLE_LCD_PARAM_BITS if your hypothetical 16-bit device uses 16-bit commands/parameters.
   • Modify the data_pattern to be an array of uint16_t and adapt the sending functions. Observe the output on a logic analyzer (if you have enough channels).

Summary

• Parallel I/O (ParIO) offers high-speed data transfer by sending multiple bits simultaneously over several data lines.
• It’s commonly used for peripherals like LCDs and cameras where high throughput is essential.
• The Intel 8080 interface is a common asynchronous parallel standard using data lines, CS, WR, RD, and D/C signals.
• Newer ESP32 variants (S2, S3, C6, H2) have dedicated LCD_CAM hardware supporting parallel interfaces, often utilizing DMA.
• The ESP-IDF esp_lcd driver (specifically esp_lcd_panel_io_i80) provides APIs to configure and use 8080-style parallel interfaces on supported SoCs.
• Proper GPIO selection, D/C logic, timing (pclk_hz), and DMA considerations are crucial for successful ParIO implementation.
• A logic analyzer is an invaluable tool for debugging parallel interface signals.

Further Reading

• ESP-IDF API Reference – LCD Controller: https://docs.espressif.com/projects/esp-idf/en/v5.x/esp32s3/api-reference/peripherals/lcd.html (Navigate to your specific ESP32 variant if not S3).
• ESP32-S3 Technical Reference Manual: (Search for “LCD Controller” or “Camera Controller” sections) https://www.espressif.com/sites/default/files/documentation/esp32-s3_technical_reference_manual_en.pdf
• Intel 8080/8085 User Manuals: For historical context and detailed understanding of the 8080 bus signals and timing (general web search).