MCU---HLK-W801 parallel port driver ST7789

Purpose

I bought this parallel port screen to make a NES emulator game console. The SPI screen I used before was quite time-consuming to display the game screen because it was serial data. So I planned to try the parallel port screen and understand the driving method of the parallel port 8080.

Parallel Port Protocol

The 8080 timing is also called the Intel bus, which is usually found on LCDs in MCU (MPU) mode.

There are four Inter bus control lines:

RD: Write Enable

WR: Read Enable

DC(RS): - Data/Command

CS: Chip Select

Then there are several data lines, such as 8 or 16.

Write timing diagram

Reading Timing Diagram

It is important to note that the reading and writing of data are both valid on the rising edge of RD or WR. So we can write data first and then create a rising edge, or pull it low first and then pull it high after writing data. However, from the figure, the former is recommended.

ST7789 Pin Definition

There are several ways to use ST7789. Today we will only talk about the 16-bit parallel port driver.

Hardware Hookup

#define P_LEDA_PORTGPIOA

#define P_LEDA_PINGPIO_PIN_5//Backlight

#define P_RD_PORTGPIOA

#define P_RD_PINGPIO_PIN_9 //RD

#define P_WR_PORTGPIOA

#define P_WR_PINGPIO_PIN_10 //WR

#define P_CD_PORTGPIOA

#define P_CD_PINGPIO_PIN_11 //RS 0 is command 1: data

#define P_CS_PORTGPIOA

#define P_CS_PINGPIO_PIN_12 //cs 0 is selected

#define P_RESET_PORTGPIOA

#define P_RESET_PINGPIO_PIN_14 //REST

#define P_DATA_PORTGPIOB

#define P_DATA_PIN0xFFFF

in,

Backlight, some screens are called BLK, we can directly connect to the high level.

CS, we can directly connect it to low level, which is selected by default.

RD, we can directly pull the level high without the read function.

CD, some screens are called RS.

We use GPIOB 0~15 for data lines. Be careful here, or the screen will be distorted if you connect them wrong.

Then define the following control macro

#define P_CD_LOWP_CD_PORT->DATA &= ~P_CD_PIN

#define P_CD_HIGHP_CD_PORT->DATA |= P_CD_PIN

#define P_RESET_LOWP_RESET_PORT->DATA &= ~P_RESET_PIN

#define P_RESET_HIGHP_RESET_PORT->DATA |= P_RESET_PIN

#define P_WR_LOWP_WR_PORT->DATA &= ~P_WR_PIN

#define P_WR_HIGHP_WR_PORT->DATA |= P_WR_PIN

Here is how w801 is written, with the pins set high and low.

ST7789 core functions

The two most basic control functions of LCD display are writing registers and writing data.

void P_WriteReg(uint16_t reg)

{

P_CD_LOW;

WRITE_REG(P_DATA_PORT->DATA,reg);

P_WR_LOW;

P_WR_HIGH;

P_CD_HIGH;

}

void P_WriteData(uint16_t data)

{

WRITE_REG(P_DATA_PORT->DATA,data);

P_WR_LOW;

P_WR_HIGH;

}

Here we focus the modification of the control lines entirely on the write registers, because the write registers are used less frequently, so when writing data, the efficiency is higher.

Then the initialization function

void LCD_Init(void)

{

LCD_Reset_On();

HAL_Delay(120);

LCD_Reset_Off();

HAL_Delay(120);

LCD_WriteReg(0x3A);   //65k mode

LCD_WriteData8(0x05);

LCD_WriteReg(0xC5); //VCOM

LCD_WriteData8(0x1A);

LCD_WriteReg(0x36);//Screen display direction settings

LCD_WriteData8(0x00);

//-------------ST7789V Frame rate setting-----------//

LCD_WriteReg(0xb2);

LCD_WriteData8(0x05);

LCD_WriteData8(0x05);

LCD_WriteData8(0x00);

LCD_WriteData8(0x33);

LCD_WriteData8(0x33);

LCD_WriteReg(0xb7);

LCD_WriteData8(0x35);

//--------------ST7789V Power setting---------------//

LCD_WriteReg(0xBB);//VCOM

LCD_WriteData8(0x3F);

LCD_WriteReg(0xC0); //Power control

LCD_WriteData8(0x2c);

LCD_WriteReg(0xC2);

LCD_WriteData8(0x01);

LCD_WriteReg(0xC3);

LCD_WriteData8(0x0F); //0Dgvd

LCD_WriteReg(0xC4);

LCD_WriteData8(0x20);

LCD_WriteReg(0xC6);

LCD_WriteData8(0X11); //0x0F

LCD_WriteReg(0xd0);

LCD_WriteData8(0xa4);

LCD_WriteData8(0xa1);

LCD_WriteReg(0xE8);

LCD_WriteData8(0x03);

LCD_WriteReg(0xE9);

LCD_WriteData8(0x09);

LCD_WriteData8(0x09);

LCD_WriteData8(0x08);

//---------------ST7789V gamma setting-------------//

LCD_WriteReg(0xE0); //Set Gamma

LCD_WriteData8(0xD0);

LCD_WriteData8(0x05);

LCD_WriteData8(0x09);

LCD_WriteData8(0x09);

LCD_WriteData8(0x08);

LCD_WriteData8(0x14);

LCD_WriteData8(0x28);

LCD_WriteData8(0x33);

LCD_WriteData8(0x3F);

LCD_WriteData8(0x07);

LCD_WriteData8(0x13);

LCD_WriteData8(0x14);

LCD_WriteData8(0x28);

LCD_WriteData8(0x30);

LCD_WriteReg(0XE1); //Set Gamma

LCD_WriteData8(0xD0);

LCD_WriteData8(0x05);

LCD_WriteData8(0x09);

LCD_WriteData8(0x09);

LCD_WriteData8(0x08);

LCD_WriteData8(0x03);

LCD_WriteData8(0x24);

LCD_WriteData8(0x32);

LCD_WriteData8(0x32);

LCD_WriteData8(0x3B);

LCD_WriteData8(0x14);

LCD_WriteData8(0x13);

LCD_WriteData8(0x28);

LCD_WriteData8(0x2F);

LCD_WriteReg(0x11);

HAL_Delay(120);

LCD_Clear(0x0000);/*Manually clear the screen before displaying to prevent screen distortion*/

LCD_WriteReg(0x29);//Turn on display 

}

The screen orientation can be modified

LCD_WriteReg(0x36); //Screen display direction setting

LCD_WriteData8(0x00);

0x00 is the normal vertical screen

0xA0 is horizontal screen to the left

There are two other types, 0x60 and 0xC0, which are probably inverted and horizontal to the right. If you are interested, you can try them.

Error-prone points

The most error-prone part of the 16-bit driver is the coordinate setting. I thought the coordinates were 16 bits, so I could just write four coordinates. This is exactly wrong. It needs to be compatible with 8 bits, and each 16 bits must be written twice. Otherwise, there will be a screen distortion problem.

I spent a day to fix this bug.

void LCD_Address_Set(uint16_t xs, uint16_t ys, uint16_t xe, uint16_t ye)

{

LCD_WriteReg(0x2a);

LCD_WriteData(xs>>8);

LCD_WriteData(xs&0xff);

LCD_WriteData(xe>>8);

LCD_WriteData(xe&0xff);

LCD_WriteReg(0x2b);

LCD_WriteData(ys>>8);

LCD_WriteData(ys&0xff);

LCD_WriteData(ye>>8);

LCD_WriteData(ye&0xff);

LCD_WriteReg(0x2c);

}