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Working with STM32 and Graphics LCD: GLCD 128×64 ST7920

Posted in Embedded Systems, LCD, Peripheral Drivers, STM32

In this guide, we shall interface STM32 with GLCD12864 using serial method. We shall display some texts, shapes and graphics.

In the guide, we will cover the following:

  • GLCD 12864.
  • Interface with STM32.
  • Code.
  • Demo.

1. GLCD 12864:

Ordinary LCDs can only display simple text or numbers within a fixed size. But in 128×64 graphical LCD display, there is 128×64 = 8192 dots, which is equivalent to 8242/8 = 1024 pixels. So, it can display not only simple text or numbers within a fixed size but also simple graphics.

128×64 Graphical LCD Display Pinout

This module has 20 pins:

  • GND: Ground
  • VCC: Module power supply – 5 V
  • VO: LCD Contrast
  • RS: Register Select Pin
  • R/W: Write/ Read selection
  • E: Enable Signal
  • D0-7: Data Bus
  • PSB: Interface selection (0 for serial communication, 1 for 8-bit parallel communication)
  • NC: Not Connected
  • RST: Reset
  • Vout: LCD Voltage Output (Vout < 7V)
  • BLA: Power Supply for Backlight+
  • BLK: Power Supply for Backlight-

You can see the pinout of this module in the image below.

2. Interface with STM32:

setup below is as follows
PA0 ———> SCLK (EN)
PA1 ———> CS (RS)
PA4 ———> SID (RW)
PA8 ———> RST (RST)

3. Code:

We start of by defining some marcos fpr SCLK, CS, SID and RST as following:

#define SCK_LOW 	(GPIOA->BSRR=GPIO_BSRR_BR0)
#define SCK_HIGH 	(GPIOA->BSRR=GPIO_BSRR_BS0)

#define CS_LOW 		(GPIOA->BSRR=GPIO_BSRR_BR1)
#define CS_HIGH 	(GPIOA->BSRR=GPIO_BSRR_BS1)

#define SID_LOW 	(GPIOA->BSRR=GPIO_BSRR_BR4)
#define SID_HIGH 	(GPIOA->BSRR=GPIO_BSRR_BS4)

#define RST_LOW 	(GPIOA->BSRR=GPIO_BSRR_BR8)
#define RST_HIGH 	(GPIOA->BSRR=GPIO_BSRR_BS8)

Now we can need some variables as following:

uint8_t startRow, startCol, endRow, endCol; // coordinates of the dirty rectangle
uint8_t numRows = 64;
uint8_t numCols = 128;
uint8_t Graphic_Check = 0;
uint8_t image[(128 * 64)/8];

For initializing the lcd:

void ST7920_Init (void)
{
	
	RCC->AHB1ENR|=RCC_AHB1ENR_GPIOAEN;
	GPIOA->MODER|=(GPIO_MODER_MODE0_0|GPIO_MODER_MODE1_0|GPIO_MODER_MODE4_0|GPIO_MODER_MODE8_0);
	GPIOA->MODER&=~(GPIO_MODER_MODE0_1|GPIO_MODER_MODE1_1|GPIO_MODER_MODE4_1|GPIO_MODER_MODE8_1);
	GPIOA->OSPEEDR|=GPIO_OSPEEDER_OSPEEDR0|GPIO_OSPEEDER_OSPEEDR1|GPIO_OSPEEDER_OSPEEDR4|GPIO_OSPEEDER_OSPEEDR8;
	
	RST_LOW; 					// RESET=0
	delay(10);   // wait for 10ms
	RST_HIGH;

	delay(50);   //wait for >40 ms


	ST7920_SendCmd(0x30);  // 8bit mode
	delayUs(110);  //  >100us delay

	ST7920_SendCmd(0x30);  // 8bit mode
	delayUs(40);  // >37us delay

	ST7920_SendCmd(0x08);  // D=0, C=0, B=0
	delayUs(110);  // >100us delay

	ST7920_SendCmd(0x01);  // clear screen
	delay(12);  // >10 ms delay


	ST7920_SendCmd(0x06);  // cursor increment right no shift
	delay(1);  // 1ms delay

	ST7920_SendCmd(0x0C);  // D=1, C=0, B=0
    delay(1);  // 1ms delay

	ST7920_SendCmd(0x02);  // return to home
	delay(1);  // 1ms delay

}

Since we are using serial mode, we need to use software SPI to send data to the LCD as following:

static void SendByteSPI(uint8_t byte)
{
	for(int i=0;i<8;i++)
	{
		if((byte<<i)&0x80)
			{
				SID_HIGH;  // SID=1  OR MOSI
			}

		else {SID_LOW;}  // SID=0

		SCK_LOW;  // SCLK =0  OR SCK
		SCK_HIGH;  // SCLK=1
}
}

For sending data and command as following:


static void ST7920_SendCmd (uint8_t cmd)
{

	CS_HIGH;  // PUll the CS high

	SendByteSPI(0xf8+(0<<1));  // send the SYNC + RS(0)
	SendByteSPI(cmd&0xf0);  // send the higher nibble first
	SendByteSPI((cmd<<4)&0xf0);  // send the lower nibble
	delayUs(50);

	CS_LOW;  // PUll the CS LOW

}

static void ST7920_SendData (uint8_t data)
{

	CS_HIGH;

	SendByteSPI(0xf8+(1<<1));  // send the SYNC + RS(1)
	SendByteSPI(data&0xf0);  // send the higher nibble first
	SendByteSPI((data<<4)&0xf0);  // send the lower nibble
	delayUs(50);
	CS_LOW;  // PUll the CS LOW
}

For displaying text as following:

void ST7920_SendString(int row, int col, char* string)
{
    switch (row)
    {
        case 0:
            col |= 0x80;
            break;
        case 1:
            col |= 0x90;
            break;
        case 2:
            col |= 0x88;
            break;
        case 3:
            col |= 0x98;
            break;
        default:
            col |= 0x80;
            break;
    }

    ST7920_SendCmd(col);

    while (*string)
    	{
    		ST7920_SendData(*string++);
    	}
}

Switch to graphic mode:

void ST7920_GraphicMode (int enable)   // 1-enable, 0-disable
{
	if (enable == 1)
	{
		ST7920_SendCmd(0x30);  // 8 bit mode
		delay (1);
		ST7920_SendCmd(0x34);  // switch to Extended instructions
		delay (1);
		ST7920_SendCmd(0x36);  // enable graphics
		delay (1);
		Graphic_Check = 1;  // update the variable
	}

	else if (enable == 0)
	{
		ST7920_SendCmd(0x30);  // 8 bit mode
		delay (1);
		Graphic_Check = 0;  // update the variable
	}
}

For drawing some graphics:

void ST7920_DrawBitmap(const unsigned char* graphic)
{
	uint8_t x, y;
	for(y = 0; y < 64; y++)
	{
		if(y < 32)
		{
			for(x = 0; x < 8; x++)							// Draws top half of the screen.
			{												// In extended instruction mode, vertical and horizontal coordinates must be specified before sending data in.
				ST7920_SendCmd(0x80 | y);				// Vertical coordinate of the screen is specified first. (0-31)
				ST7920_SendCmd(0x80 | x);				// Then horizontal coordinate of the screen is specified. (0-8)
				ST7920_SendData(graphic[2*x + 16*y]);		// Data to the upper byte is sent to the coordinate.
				ST7920_SendData(graphic[2*x+1 + 16*y]);	// Data to the lower byte is sent to the coordinate.
			}
		}
		else
		{
			for(x = 0; x < 8; x++)							// Draws bottom half of the screen.
			{												// Actions performed as same as the upper half screen.
				ST7920_SendCmd(0x80 | (y-32));			// Vertical coordinate must be scaled back to 0-31 as it is dealing with another half of the screen.
				ST7920_SendCmd(0x88 | x);
				ST7920_SendData(graphic[2*x + 16*y]);
				ST7920_SendData(graphic[2*x+1 + 16*y]);
			}
		}

	}
}


// Update the display with the selected graphics
void ST7920_Update(void)
{
	ST7920_DrawBitmap(image);
}

Clearing the display:


void ST7920_Clear()
{
	if (Graphic_Check == 1)  // if the graphic mode is set
	{
		uint8_t x, y;
		for(y = 0; y < 64; y++)
		{
			if(y < 32)
			{
				ST7920_SendCmd(0x80 | y);
				ST7920_SendCmd(0x80);
			}
			else
			{
				ST7920_SendCmd(0x80 | (y-32));
				ST7920_SendCmd(0x88);
			}
			for(x = 0; x < 8; x++)
			{
				ST7920_SendData(0);
				ST7920_SendData(0);
			}
		}
	}

	else
	{
		ST7920_SendCmd(0x01);   // clear the display using command
		//delay(2); // delay >1.6 ms
	}
}

Extra functions needed:

// set Pixel

void SetPixel(uint8_t x, uint8_t y)
{
  if (y < numRows && x < numCols)
  {
    uint8_t *p = image + ((y * (numCols/8)) + (x/8));
    *p |= 0x80u >> (x%8);

    *image = *p;

    // Change the dirty rectangle to account for a pixel being dirty (we assume it was changed)
    if (startRow > y) { startRow = y; }
    if (endRow <= y)  { endRow = y + 1; }
    if (startCol > x) { startCol = x; }
    if (endCol <= x)  { endCol = x + 1; }


  }

}

/* draw a line
 * start point (X0, Y0)
 * end point (X1, Y1)
 */
void DrawLine(uint8_t x0, uint8_t y0, uint8_t x1, uint8_t y1)
{
  int dx = (x1 >= x0) ? x1 - x0 : x0 - x1;
  int dy = (y1 >= y0) ? y1 - y0 : y0 - y1;
  int sx = (x0 < x1) ? 1 : -1;
  int sy = (y0 < y1) ? 1 : -1;
  int err = dx - dy;

  for (;;)
  {
    SetPixel(x0, y0);
    if (x0 == x1 && y0 == y1) break;
    int e2 = err + err;
    if (e2 > -dy)
    {
      err -= dy;
      x0 += sx;
    }
    if (e2 < dx)
    {
      err += dx;
      y0 += sy;
    }
  }
}




/* Draw rectangle
 * start point (x,y)
 * w -> width
 * h -> height
 */
void DrawRectangle(uint16_t x, uint16_t y, uint16_t w, uint16_t h)
{
	/* Check input parameters */
	if (
		x >= numCols ||
		y >= numRows
	) {
		/* Return error */
		return;
	}

	/* Check width and height */
	if ((x + w) >= numCols) {
		w = numCols - x;
	}
	if ((y + h) >= numRows) {
		h = numRows - y;
	}

	/* Draw 4 lines */
	DrawLine(x, y, x + w, y);         /* Top line */
	DrawLine(x, y + h, x + w, y + h); /* Bottom line */
	DrawLine(x, y, x, y + h);         /* Left line */
	DrawLine(x + w, y, x + w, y + h); /* Right line */
}




/* Draw filled rectangle
 * Start point (x,y)
 * w -> width
 * h -> height
 */
void DrawFilledRectangle(uint16_t x, uint16_t y, uint16_t w, uint16_t h)
{
	uint8_t i;

	/* Check input parameters */
	if (
		x >= numCols ||
		y >= numRows
	) {
		/* Return error */
		return;
	}

	/* Check width and height */
	if ((x + w) >= numCols) {
		w = numCols - x;
	}
	if ((y + h) >= numRows) {
		h = numRows - y;
	}

	/* Draw lines */
	for (i = 0; i <= h; i++) {
		/* Draw lines */
		DrawLine(x, y + i, x + w, y + i);
	}
}




/* draw circle
 * centre (x0,y0)
 * radius = radius
 */
void DrawCircle(uint8_t x0, uint8_t y0, uint8_t radius)
{
  int f = 1 - (int)radius;
  int ddF_x = 1;

  int ddF_y = -2 * (int)radius;
  int x = 0;

  SetPixel(x0, y0 + radius);
  SetPixel(x0, y0 - radius);
  SetPixel(x0 + radius, y0);
  SetPixel(x0 - radius, y0);

  int y = radius;
  while(x < y)
  {
    if(f >= 0)
    {
      y--;
      ddF_y += 2;
      f += ddF_y;
    }
    x++;
    ddF_x += 2;
    f += ddF_x;
    SetPixel(x0 + x, y0 + y);
    SetPixel(x0 - x, y0 + y);
    SetPixel(x0 + x, y0 - y);
    SetPixel(x0 - x, y0 - y);
    SetPixel(x0 + y, y0 + x);
    SetPixel(x0 - y, y0 + x);
    SetPixel(x0 + y, y0 - x);
    SetPixel(x0 - y, y0 - x);
  }
}


// Draw Filled Circle

void DrawFilledCircle(int16_t x0, int16_t y0, int16_t r)
{
	int16_t f = 1 - r;
	int16_t ddF_x = 1;
	int16_t ddF_y = -2 * r;
	int16_t x = 0;
	int16_t y = r;

    SetPixel(x0, y0 + r);
    SetPixel(x0, y0 - r);
    SetPixel(x0 + r, y0);
    SetPixel(x0 - r, y0);
    DrawLine(x0 - r, y0, x0 + r, y0);

    while (x < y) {
        if (f >= 0) {
            y--;
            ddF_y += 2;
            f += ddF_y;
        }
        x++;
        ddF_x += 2;
        f += ddF_x;

        DrawLine(x0 - x, y0 + y, x0 + x, y0 + y);
        DrawLine(x0 + x, y0 - y, x0 - x, y0 - y);

        DrawLine(x0 + y, y0 + x, x0 - y, y0 + x);
        DrawLine(x0 + y, y0 - x, x0 - y, y0 - x);
    }
}



// Draw Traingle with coordimates (x1, y1), (x2, y2), (x3, y3)
void DrawTriangle(uint16_t x1, uint16_t y1, uint16_t x2, uint16_t y2, uint16_t x3, uint16_t y3)
{
	/* Draw lines */
	DrawLine(x1, y1, x2, y2);
	DrawLine(x2, y2, x3, y3);
	DrawLine(x3, y3, x1, y1);
}



// Draw Filled Traingle with coordimates (x1, y1), (x2, y2), (x3, y3)
void DrawFilledTriangle(uint16_t x1, uint16_t y1, uint16_t x2, uint16_t y2, uint16_t x3, uint16_t y3)
{
	int16_t deltax = 0, deltay = 0, x = 0, y = 0, xinc1 = 0, xinc2 = 0,
	yinc1 = 0, yinc2 = 0, den = 0, num = 0, numadd = 0, numpixels = 0,
	curpixel = 0;

#define ABS(x)   ((x) > 0 ? (x) : -(x))

	deltax = ABS(x2 - x1);
	deltay = ABS(y2 - y1);
	x = x1;
	y = y1;

	if (x2 >= x1) {
		xinc1 = 1;
		xinc2 = 1;
	} else {
		xinc1 = -1;
		xinc2 = -1;
	}

	if (y2 >= y1) {
		yinc1 = 1;
		yinc2 = 1;
	} else {
		yinc1 = -1;
		yinc2 = -1;
	}

	if (deltax >= deltay){
		xinc1 = 0;
		yinc2 = 0;
		den = deltax;
		num = deltax / 2;
		numadd = deltay;
		numpixels = deltax;
	} else {
		xinc2 = 0;
		yinc1 = 0;
		den = deltay;
		num = deltay / 2;
		numadd = deltax;
		numpixels = deltay;
	}

	for (curpixel = 0; curpixel <= numpixels; curpixel++)
	{
		DrawLine(x, y, x3, y3);

		num += numadd;
		if (num >= den) {
			num -= den;
			x += xinc1;
			y += yinc1;
		}
		x += xinc2;
		y += yinc2;
	}
}

You may download the entire code from here:

GLCDDownload

4. Demo:

Happy coding 🙂

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3 Comments

  • Amin Posted February 8, 2023 7:03 pm

    Hi, nice work
    thank you

    Reply
  • sushma gawde Posted March 20, 2024 10:17 am

    how to set cursor position at particular row and column position

    Reply

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