ST7796 LCD Controller driver
Overview
The ST7796S is a single-chip controller/driver for 262K-color, graphic type TFT-LCD. It consists of 960 source lines and 480 gate lines driving circuits. The ST7796S is capable of connecting directly to an external microprocessor, and accepts 8-bit/9-bit/16-bit/18-bit parallel interface, SPI, and the ST7796S also provides MIPI interface. Display data can be stored in the on-chip display data RAM of 320x480x18 bits. It can perform display data RAM read-/write-operation with no external clock to minimize power consumption. In addition, because of the integrated power supply circuit necessary to drive liquid crystal; it is possible to make a display system with fewest components.
The ST7796 LCD controller driver is a platform-agnostic driver, based on the generic MIPI driver. It implements display initialization, supports display rotation and implements the display flush callback. The user needs to implement only two platform-specific functions to send a command or pixel data to the controller via SPI or parallel bus. Typically these are implemented by calling the appropriate SDK library functions on the given platform.
Prerequisites
There are no prerequisites.
Configuring the driver
Enable the ST7796 driver support in lv_conf.h, by cmake compiler define or by KConfig
#define LV_USE_ST7796 1
Usage
You need to implement two platform-dependent functions:
/* Send short command to the LCD. This function shall wait until the transaction finishes. */
int32_t my_lcd_send_cmd(lv_display_t *disp, const uint8_t *cmd, size_t cmd_size, const uint8_t *param, size_t param_size)
{
...
}
/* Send large array of pixel data to the LCD. If necessary, this function has to do the byte-swapping. This function can do the transfer in the background. */
int32_t my_lcd_send_color(lv_display_t *disp, const uint8_t *cmd, size_t cmd_size, uint8_t *param, size_t param_size)
{
...
}
To create an ST7796-based display use the function
/**
* Create an LCD display with ST7796 driver
* @param hor_res horizontal resolution
* @param ver_res vertical resolution
* @param flags default configuration settings (mirror, RGB ordering, etc.)
* @param send_cmd platform-dependent function to send a command to the LCD controller (usually uses polling transfer)
* @param send_color platform-dependent function to send pixel data to the LCD controller (usually uses DMA transfer: must implement a 'ready' callback)
* @return pointer to the created display
*/
lv_display_t * lv_st7796_create(uint32_t hor_res, uint32_t ver_res, lv_lcd_flag_t flags,
lv_st7796_send_cmd_cb_t send_cmd_cb, lv_st7796_send_color_cb_t send_color_cb);
For additional details and a working example see the generic MIPI driver documentation.
Note
You can find a step-by-step guide and the actual implementation of the callbacks on an STM32F746 using STM32CubeIDE and the ST HAL libraries here: Step-by-step Guide: How to use the LVGL v9 LCD drivers with STM32 devices