LCD¶

ESP32S3 Minimal System Board with 0.96-Inch HD IPS LCD Display¶

The onboard 0.96-inch HD IPS LCD display has a resolution of 160x80 and supports 16-bit true color display. The display uses the ST7735S driver chip with built-in RAM, eliminating the need for external drivers or memory. The ESP32S3 chip can drive this display via the SPI interface. In 4-wire SPI communication mode, the 0.96-inch LCD screen requires only four signal lines (CS, SCL, SDA, RS (DC)).

The screen connects to the PCB circuit via 13 pins. The pin details are as follows:

From the above diagrams, it is evident that the write cycle of the 0.96-inch LCD module in 4-wire SPI mode is very fast (TSCYCW = 66ns), whereas the read cycle is relatively slower (TSCYCR = 150ns).

The ST7735S LCD driver stores display data directly in its onboard RAM, which has a capacity of 132x162x18 bits. The ST7735S chip automatically displays data from its RAM to the LCD without an external clock, minimizing power consumption.

Hardware Reset Requirements¶

Before initializing the display module, the RST pin must be used to perform a hardware reset. The RST pin should be pulled low for at least 10 microseconds. After pulling RST high to end the reset, a delay of 120 milliseconds is required before data can be transmitted to the display module.

Backlight Control¶

The LEDK pin controls the LCD backlight of the display module. This pin has a built-in pull-down resistor. The backlight is off when the LEDK pin is high or floating and turns on when the LEDK pin is pulled low.

Color Depth¶

The ST7735S supports a maximum color depth of 18 bits (262K colors), but 16-bit color depth (65K colors) is generally used for maximum speed. In 16-bit mode, the RGB565 format is used to transmit and store color data, as shown below:

• High 5 bits represent red.
• Middle 6 bits represent green.
• Low 5 bits represent blue.
• Larger values correspond to darker colors.

Continuous RAM Read/Write and Scan Direction Configuration¶

The ST7735S allows continuous read/write operations in its RAM for color data on the LCD. The scan direction (RAM auto-increment direction) can be configured using command 0x36, as shown below:

Command 0x36 configures six parameters, but only MY, MX, and MV are relevant for setting the LCD scan direction:

This flexibility allows efficient content rendering, such as displaying BMP images that decode data starting from the bottom-left corner. By setting the LCD scan direction appropriately, data can be filled into the LCD without repeatedly setting coordinates, improving display speed.

Setting Address for Color Data¶

Before writing color data to the ST7735S, the address must be set to specify which pixel on the LCD will receive the color data. Commands 0x2A and 0x2B are used to set the column and row addresses, respectively:

• Command 0x2A:
  

• Command 0x2B:
  

With the default LCD scan direction (left to right, top to bottom), the XS and XE parameters of command 0x2A and the YS and YE parameters of command 0x2B define a region on the LCD. During continuous read/write operations, the ST7735S reads/writes color data in this region following the configured scan direction.

Dependencies¶

Key Functions¶

/* Function declarations */
void lcd_init(void);                                                                                                  /* Initialize the LCD */
void lcd_clear(uint16_t color);                                                                                       /* Clear the screen */
void lcd_scan_dir(uint8_t dir);                                                                                       /* Set the LCD auto scan direction */
void lcd_write_data(const uint8_t *data, int len);                                                                    /* Write data to the LCD */
void lcd_write_data16(uint16_t data);                                                                                 /* Write 16-bit data to the LCD */
void lcd_set_cursor(uint16_t xpos, uint16_t ypos);                                                                    /* Set the cursor position */
void lcd_set_window(uint16_t xstar, uint16_t ystar, uint16_t xend, uint16_t yend);                                    /* Set the display window size */
void lcd_fill(uint16_t sx, uint16_t sy, uint16_t ex, uint16_t ey, uint16_t color);                                    /* Fill a specific area with a single color */
void lcd_show_num(uint16_t x, uint16_t y, uint32_t num, uint8_t len, uint8_t size, uint16_t color);                   /* Display a number with len digits */
void lcd_show_xnum(uint16_t x, uint16_t y, uint32_t num, uint8_t len, uint8_t size, uint8_t mode, uint16_t color);    /* Display an extended number with len digits */
void lcd_show_string(uint16_t x, uint16_t y, uint16_t width, uint16_t height, uint8_t size, char *p, uint16_t color); /* Display a string */
void lcd_draw_rectangle(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, uint16_t color);                          /* Draw a rectangle */
void lcd_draw_hline(uint16_t x, uint16_t y, uint16_t len, uint16_t color);                                            /* Draw a horizontal line */
void lcd_draw_line(uint16_t x1, uint16_t y1, uint16_t x2, uint16_t y2, uint16_t color);                               /* Draw a straight or slanted line */
void lcd_draw_pixel(uint16_t x, uint16_t y, uint16_t color);                                                          /* Draw a pixel */
void lcd_show_char(uint16_t x, uint16_t y, uint8_t chr, uint8_t size, uint8_t mode, uint16_t color);                  /* Display a character at a specified position */