LCD

Introduction

ESP chips can generate various kinds of timings needed by common LCDs on the market, like SPI LCD, I2C LCD, Parallel LCD (Intel 8080), RGB/SRGB LCD, MIPI DSI LCD and etc. The esp_lcd component offers an abstracted driver framework to support them in a unified way.

An LCD typically consists of two main planes:

Control Plane: This plane allows us to read and write to the internal registers of the LCD device controller. Host typically uses this plane for tasks such as initializing the LCD power supply and performing gamma calibration.
Data Plane: The data plane is responsible for transmitting pixel data to the LCD device.

Functional Overview

In the context of esp_lcd, both the data plane and the control plane are represented by the esp_lcd_panel_handle_t type.

On some LCDs, these two planes may be combined into a single plane. In this configuration, pixel data is transmitted through the control plane, achieving functionality similar to that of the data plane. This merging is common in SPI LCDs and I2C LCDs. Additionally, there are LCDs that do not require a separate control plane. For instance, certain RGB LCDs automatically execute necessary initialization procedures after power-up. Host devices only need to continuously refresh pixel data through the data plane. However, it's essential to note that not all RGB LCDs eliminate the control plane entirely. Some LCD devices can simultaneously support multiple interfaces, requiring the host to send specific commands via the control plane (such as those based on the SPI interface) to enable the RGB mode.

This document will discuss how to create the control plane and data plane, as mentioned earlier, based on different types of LCDs.

备注

ESP-IDF provides only a limited number of LCD device controller drivers out of the box (e.g., ST7789), more drivers are available in the Espressif Component Registry.

LCD Control Panel Operations

esp_lcd_panel_reset() can reset the LCD control panel.
esp_lcd_panel_init() performs a basic initialization of the control panel. To perform more manufacture specific initialization, please refer to Steps to Add Manufacture Specific Initialization.
By combining using esp_lcd_panel_swap_xy() and esp_lcd_panel_mirror(), you can achieve the functionality of rotating or mirroring the LCD screen.
esp_lcd_panel_disp_on_off() can turn on or off the LCD screen by cutting down the output path from the frame buffer to the LCD screen. Please note, this is not controlling the LCD backlight. Backlight control is not covered by the esp_lcd driver.
esp_lcd_panel_disp_sleep() can reduce the power consumption of the LCD screen by entering the sleep mode. The internal frame buffer is still retained.

LCD Data Panel Operations

esp_lcd_panel_reset() can reset the LCD data panel.
esp_lcd_panel_init() performs a basic initialization of the data panel.
esp_lcd_panel_draw_bitmap() is the function which does the magic to flush the user draw buffer to the LCD screen, where the target draw window is configurable. Please note, this function expects the draw buffer is a 1-D array and there's no stride in between each lines.

Steps to Add Manufacture Specific Initialization

The LCD controller drivers (e.g., st7789) in ESP-IDF only provide basic initialization in the esp_lcd_panel_init(), leaving the vast majority of settings to the default values. Some LCD modules needs to set a bunch of manufacture specific configurations before it can display normally. These configurations usually include gamma, power voltage and so on. If you want to add manufacture specific initialization, please follow the steps below:

esp_lcd_panel_reset(panel_handle);
esp_lcd_panel_init(panel_handle);
// set extra configurations e.g., gamma control
// with the underlying IO handle
// please consult your manufacture for special commands and corresponding values
esp_lcd_panel_io_tx_param(io_handle, GAMMA_CMD, (uint8_t[]) {
       GAMMA_ARRAY
    }, N);
// turn on the display
esp_lcd_panel_disp_on_off(panel_handle, true);

Application Example

Software JPEG decoding and display - peripherals/lcd/tjpgd

API Reference

Header File

components/hal/include/hal/lcd_types.h
This header file can be included with:
#include "hal/lcd_types.h"

Type Definitions

typedef int lcd_clock_source_t

Enumerations

enum lcd_rgb_data_endian_t

RGB data endian.

Values:

enumerator LCD_RGB_DATA_ENDIAN_BIG: RGB data endian: MSB first

enumerator LCD_RGB_DATA_ENDIAN_LITTLE: RGB data endian: LSB first

enum lcd_color_space_t

LCD color space.

Values:

enumerator LCD_COLOR_SPACE_RGB: Color space: RGB

enumerator LCD_COLOR_SPACE_YUV: Color space: YUV

enum lcd_color_rgb_pixel_format_t

LCD color pixel format in RGB color space.

Values:

enumerator LCD_COLOR_PIXEL_FORMAT_RGB565: 16 bits, 5 bits per R/B value, 6 bits for G value

enumerator LCD_COLOR_PIXEL_FORMAT_RGB666: 18 bits, 6 bits per R/G/B value

enumerator LCD_COLOR_PIXEL_FORMAT_RGB888: 24 bits, 8 bits per R/G/B value

enum lcd_color_format_t

LCD color format.

Values:

enumerator LCD_COLOR_FMT_RGB565: RGB565.

enumerator LCD_COLOR_FMT_RGB666: RGB666.

enumerator LCD_COLOR_FMT_RGB888: RGB888.

enumerator LCD_COLOR_FMT_YUV422: YUV422.

enum lcd_color_range_t

LCD color range.

Values:

enumerator LCD_COLOR_RANGE_LIMIT: Limited color range

enumerator LCD_COLOR_RANGE_FULL: Full color range

enum lcd_yuv_sample_t

YUV sampling method.

Values:

enumerator LCD_YUV_SAMPLE_422: YUV 4:2:2 sampling

enumerator LCD_YUV_SAMPLE_420: YUV 4:2:0 sampling

enumerator LCD_YUV_SAMPLE_411: YUV 4:1:1 sampling

enum lcd_yuv_conv_std_t

The standard used for conversion between RGB and YUV.

Values:

enumerator LCD_YUV_CONV_STD_BT601: YUV<->RGB conversion standard: BT.601

enumerator LCD_YUV_CONV_STD_BT709: YUV<->RGB conversion standard: BT.709

enum lcd_yuv422_pack_order_t

YUV422 packing order.

Values:

enumerator LCD_YUV422_PACK_ORDER_YUYV: YUYV

enumerator LCD_YUV422_PACK_ORDER_YVYU: YVYU

enumerator LCD_YUV422_PACK_ORDER_UYVY: UYVY

enumerator LCD_YUV422_PACK_ORDER_VYUY: VYUY

Header File

components/esp_lcd/include/esp_lcd_types.h
This header file can be included with:
#include "esp_lcd_types.h"
This header file is a part of the API provided by the esp_lcd component. To declare that your component depends on esp_lcd, add the following to your CMakeLists.txt:
REQUIRES esp_lcd
or
PRIV_REQUIRES esp_lcd

Structures

struct esp_lcd_video_timing_t

Timing parameters for the video data transmission.

Public Members

uint32_t h_size: Horizontal resolution, i.e. the number of pixels in a line

uint32_t v_size: Vertical resolution, i.e. the number of lines in the frame

uint32_t hsync_pulse_width: Horizontal sync width, in pixel clock

uint32_t hsync_back_porch: Horizontal back porch, number of pixel clock between hsync and start of line active data

uint32_t hsync_front_porch: Horizontal front porch, number of pixel clock between the end of active data and the next hsync

uint32_t vsync_pulse_width: Vertical sync width, in number of lines

uint32_t vsync_back_porch: Vertical back porch, number of invalid lines between vsync and start of frame

uint32_t vsync_front_porch: Vertical front porch, number of invalid lines between the end of frame and the next vsync

struct esp_lcd_panel_io_event_data_t: Type of LCD panel IO event data.

struct esp_lcd_panel_io_callbacks_t

Type of LCD panel IO callbacks.

Public Members

esp_lcd_panel_io_color_trans_done_cb_t on_color_trans_done: Callback invoked when color data transfer has finished

struct esp_lcd_color_conv_config_t

Configuration of LCD color conversion.

Public Members

lcd_color_range_t in_color_range: Color range of the input color

lcd_color_range_t out_color_range: Color range of the output color

lcd_yuv_conv_std_t conv_std: YUV conversion standard: BT601, BT709

lcd_yuv422_pack_order_t in_pack_order: YUV422 packing order of the input color

struct esp_lcd_color_conv_config_t::[anonymous]::[anonymous]::[anonymous] yuv422: YUV422 specific

struct esp_lcd_color_conv_config_t::[anonymous]::[anonymous] yuv: YUV specific

union esp_lcd_color_conv_config_t::[anonymous] spec: Extra configuration for specific color conversion

Type Definitions

typedef struct esp_lcd_panel_io_t *esp_lcd_panel_io_handle_t: Type of LCD panel IO handle

typedef struct esp_lcd_panel_t *esp_lcd_panel_handle_t: Type of LCD panel handle

typedef bool (*esp_lcd_panel_io_color_trans_done_cb_t)(esp_lcd_panel_io_handle_t panel_io, esp_lcd_panel_io_event_data_t *edata, void *user_ctx)

Declare the prototype of the function that will be invoked when panel IO finishes transferring color data.

Param panel_io: [in] LCD panel IO handle, which is created by factory API like esp_lcd_new_panel_io_spi()
Param edata: [in] Panel IO event data, fed by driver
Param user_ctx: [in] User data, passed from esp_lcd_panel_io_xxx_config_t
Return: Whether a high priority task has been waken up by this function

Enumerations

enum lcd_rgb_element_order_t

RGB element order.

Values:

enumerator LCD_RGB_ELEMENT_ORDER_RGB: RGB element order: RGB

enumerator LCD_RGB_ELEMENT_ORDER_BGR: RGB element order: BGR

Header File

components/esp_lcd/include/esp_lcd_panel_io.h
This header file can be included with:
#include "esp_lcd_panel_io.h"
This header file is a part of the API provided by the esp_lcd component. To declare that your component depends on esp_lcd, add the following to your CMakeLists.txt:
REQUIRES esp_lcd
or
PRIV_REQUIRES esp_lcd

Functions

esp_err_t esp_lcd_panel_io_rx_param(esp_lcd_panel_io_handle_t io, int lcd_cmd, void *param, size_t param_size)

Transmit LCD command and receive corresponding parameters.

备注

Commands sent by this function are short, so they are sent using polling transactions. The function does not return before the command transfer is completed. If any queued transactions sent by esp_lcd_panel_io_tx_color() are still pending when this function is called, this function will wait until they are finished and the queue is empty before sending the command(s).

参数

io -- [in] LCD panel IO handle, which is created by other factory API like esp_lcd_new_panel_io_spi()
lcd_cmd -- [in] The specific LCD command, set to -1 if no command needed
param -- [out] Buffer for the command data
param_size -- [in] Size of param buffer

返回

ESP_ERR_INVALID_ARG if parameter is invalid
ESP_ERR_NOT_SUPPORTED if read is not supported by transport
ESP_OK on success

esp_err_t esp_lcd_panel_io_tx_param(esp_lcd_panel_io_handle_t io, int lcd_cmd, const void *param, size_t param_size)

Transmit LCD command and corresponding parameters.

备注

Commands sent by this function are short, so they are sent using polling transactions. The function does not return before the command transfer is completed. If any queued transactions sent by esp_lcd_panel_io_tx_color() are still pending when this function is called, this function will wait until they are finished and the queue is empty before sending the command(s).

参数

io -- [in] LCD panel IO handle, which is created by other factory API like esp_lcd_new_panel_io_spi()
lcd_cmd -- [in] The specific LCD command, set to -1 if no command needed
param -- [in] Buffer that holds the command specific parameters, set to NULL if no parameter is needed for the command
param_size -- [in] Size of param in memory, in bytes, set to zero if no parameter is needed for the command

返回

ESP_ERR_INVALID_ARG if parameter is invalid
ESP_OK on success

esp_err_t esp_lcd_panel_io_tx_color(esp_lcd_panel_io_handle_t io, int lcd_cmd, const void *color, size_t color_size)

Transmit LCD RGB data.

备注

This function will package the command and RGB data into a transaction, and push into a queue. The real transmission is performed in the background (DMA+interrupt). The caller should take care of the lifecycle of the color buffer. Recycling of color buffer should be done in the callback on_color_trans_done().

参数

io -- [in] LCD panel IO handle, which is created by factory API like esp_lcd_new_panel_io_spi()
lcd_cmd -- [in] The specific LCD command, set to -1 if no command needed
color -- [in] Buffer that holds the RGB color data
color_size -- [in] Size of color in memory, in bytes

返回

ESP_ERR_INVALID_ARG if parameter is invalid
ESP_OK on success

esp_err_t esp_lcd_panel_io_del(esp_lcd_panel_io_handle_t io)

Destroy LCD panel IO handle (deinitialize panel and free all corresponding resource)

参数

io -- [in] LCD panel IO handle, which is created by factory API like esp_lcd_new_panel_io_spi()

返回

ESP_ERR_INVALID_ARG if parameter is invalid
ESP_OK on success

esp_err_t esp_lcd_panel_io_register_event_callbacks(esp_lcd_panel_io_handle_t io, const esp_lcd_panel_io_callbacks_t *cbs, void *user_ctx)

Register LCD panel IO callbacks.

参数

io -- [in] LCD panel IO handle, which is created by factory API like esp_lcd_new_panel_io_spi()
cbs -- [in] structure with all LCD panel IO callbacks
user_ctx -- [in] User private data, passed directly to callback's user_ctx

返回

ESP_ERR_INVALID_ARG if parameter is invalid
ESP_OK on success

Header File

components/esp_lcd/include/esp_lcd_panel_ops.h
This header file can be included with:
#include "esp_lcd_panel_ops.h"
This header file is a part of the API provided by the esp_lcd component. To declare that your component depends on esp_lcd, add the following to your CMakeLists.txt:
REQUIRES esp_lcd
or
PRIV_REQUIRES esp_lcd

Functions

esp_err_t esp_lcd_panel_reset(esp_lcd_panel_handle_t panel)

Reset LCD panel.

备注

Panel reset must be called before attempting to initialize the panel using esp_lcd_panel_init().

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()

返回

ESP_OK on success

esp_err_t esp_lcd_panel_init(esp_lcd_panel_handle_t panel)

Initialize LCD panel.

备注

Before calling this function, make sure the LCD panel has finished the reset stage by esp_lcd_panel_reset().

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()

返回

ESP_OK on success

esp_err_t esp_lcd_panel_del(esp_lcd_panel_handle_t panel)

Deinitialize the LCD panel.

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()

返回

ESP_OK on success

esp_err_t esp_lcd_panel_draw_bitmap(esp_lcd_panel_handle_t panel, int x_start, int y_start, int x_end, int y_end, const void *color_data)

Draw bitmap on LCD panel.

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()
x_start -- [in] Start pixel index in the target frame buffer, on x-axis (x_start is included)
y_start -- [in] Start pixel index in the target frame buffer, on y-axis (y_start is included)
x_end -- [in] End pixel index in the target frame buffer, on x-axis (x_end is not included)
y_end -- [in] End pixel index in the target frame buffer, on y-axis (y_end is not included)
color_data -- [in] RGB color data that will be dumped to the specific window range

返回

ESP_OK on success

esp_err_t esp_lcd_panel_mirror(esp_lcd_panel_handle_t panel, bool mirror_x, bool mirror_y)

Mirror the LCD panel on specific axis.

备注

Combined with esp_lcd_panel_swap_xy(), one can realize screen rotation

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()
mirror_x -- [in] Whether the panel will be mirrored about the x axis
mirror_y -- [in] Whether the panel will be mirrored about the y axis

返回

ESP_OK on success
ESP_ERR_NOT_SUPPORTED if this function is not supported by the panel

esp_err_t esp_lcd_panel_swap_xy(esp_lcd_panel_handle_t panel, bool swap_axes)

Swap/Exchange x and y axis.

备注

Combined with esp_lcd_panel_mirror(), one can realize screen rotation

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()
swap_axes -- [in] Whether to swap the x and y axis

返回

ESP_OK on success
ESP_ERR_NOT_SUPPORTED if this function is not supported by the panel

esp_err_t esp_lcd_panel_set_gap(esp_lcd_panel_handle_t panel, int x_gap, int y_gap)

Set extra gap in x and y axis.

The gap is the space (in pixels) between the left/top sides of the LCD panel and the first row/column respectively of the actual contents displayed.

备注

Setting a gap is useful when positioning or centering a frame that is smaller than the LCD.

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()
x_gap -- [in] Extra gap on x axis, in pixels
y_gap -- [in] Extra gap on y axis, in pixels

返回

ESP_OK on success

esp_err_t esp_lcd_panel_invert_color(esp_lcd_panel_handle_t panel, bool invert_color_data)

Invert the color (bit-wise invert the color data line)

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()
invert_color_data -- [in] Whether to invert the color data

返回

ESP_OK on success

esp_err_t esp_lcd_panel_disp_on_off(esp_lcd_panel_handle_t panel, bool on_off)

Turn on or off the display.

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()
on_off -- [in] True to turns on display, False to turns off display

返回

ESP_OK on success
ESP_ERR_NOT_SUPPORTED if this function is not supported by the panel

esp_err_t esp_lcd_panel_disp_off(esp_lcd_panel_handle_t panel, bool off)

Turn off the display.

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()
off -- [in] Whether to turn off the screen

返回

ESP_OK on success
ESP_ERR_NOT_SUPPORTED if this function is not supported by the panel

esp_err_t esp_lcd_panel_disp_sleep(esp_lcd_panel_handle_t panel, bool sleep)

Enter or exit sleep mode.

参数

panel -- [in] LCD panel handle, which is created by other factory API like esp_lcd_new_panel_st7789()
sleep -- [in] True to enter sleep mode, False to wake up

返回

ESP_OK on success
ESP_ERR_NOT_SUPPORTED if this function is not supported by the panel

Header File

components/esp_lcd/include/esp_lcd_panel_vendor.h
This header file can be included with:
#include "esp_lcd_panel_vendor.h"
This header file is a part of the API provided by the esp_lcd component. To declare that your component depends on esp_lcd, add the following to your CMakeLists.txt:
REQUIRES esp_lcd
or
PRIV_REQUIRES esp_lcd

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