Interfacing STM32-Discovery with ST7066u LCD

Kusala Bandara

Nov 1, 20183 min read

Updated: Nov 14, 2018

This LCD can be controlled by 4 bit bus or 8 bit bus. There are two chips in this LCD. Using each chip, you could display 80 characters.This project uses 4 bit bus for interfacing and could display 160 characters using both chips.I used IAR Systems.

Stm32-Discovery pins are wired to ST7066u as follows;

STM32-Discovery Pin Name: ST7066u Pin Name:

--------------------------- ------------------

PC0 DB4

PC1 DB5

PC2 DB6

PC3 DB7

PC13 E1(Chip1- Enable pin)

PC6 R/W

PC7 R/S

PC5 E2(Chip2-Enable pin)

GND V0(Con. adjustment pin-This must be connected to GND)

GND K(LED)

GND VSS

VCC A(LED)

VCC VDD

I encountered many problems and solved after spending hours. There are a number of things that you have to be careful about when wiring,

If you need only 2 lines to be used on LCD , only one of the enable pins (E1 or E2) has to be wired. If you need all four lines on LCD, you must wire both E1 and E2. I spent many hours trying to display on all four lines using only one chip. By wiring and enabling both chips, I could access all four lines.

V0 - Contrast Adjustment pin must be connected to GND. I tried my code without connecting V0 to GND. My code ran smoothly but display nothing on LCD. Connecting V0 to GND solved my problem.

The order of connecting pins DB4 -DB7 to PC0-P3 is important. Connecting DB4-DB7 to P3-P0 didn't give me any result since bits were shifted and gave meaningless commands,

My Code:

main.c

#include "stm32f10x.h"

#include "STM32vldiscovery.h"

#include "LCD.h"

int CHIP1=1;

int CHIP2=2;

GPIO_InitTypeDef GPIO_InitStructure;

TIM_TimeBaseInitTypeDef timerInitStructure;

void Timer_Configuration(void);

void Delay_ms(int ms);

int main(void)

{

RCC_APB2PeriphClockCmd( RCC_APB2Periph_GPIOC , ENABLE);

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE);

LCD_CtrlLinesConfig();

LCD_Init(CHIP1);

LCD_Init(CHIP2);

//setting the starting position of the cursor

//row=0, col=0,chip no=1

LCD_setCursorPosition(0,0,1);

//sending a character for chip1 to display

//char=A,data/command=Data ,chip no=1

LCD_sendByte('A',1,1);

LCD_sendByte('B',1,1);

LCD_sendByte('C',1,1);

LCD_setCursorPosition(0,7,1);

//sending a string for chip1 to display

//string="Line No 0, Chip1", chip no=1

LCD_printString("Line No 0, Chip1", 1);

LCD_setCursorPosition(1,7,1);

LCD_printString("Line No 1, Chip1", 1);

LCD_setCursorPosition(0,7,2);

LCD_printString("Line No 0, Chip2",2 );

LCD_setCursorPosition(1,7,2);

LCD_printString("Line No 1, Chip2", 2);

while (1)

{

}

void Timer_Configuration()

{

timerInitStructure.TIM_Prescaler = 23999;

timerInitStructure.TIM_CounterMode = TIM_CounterMode_Up;

timerInitStructure.TIM_Period =65535;

timerInitStructure.TIM_ClockDivision = TIM_CKD_DIV1;

timerInitStructure.TIM_RepetitionCounter = 0;

TIM_TimeBaseInit(TIM2, &timerInitStructure);

}

void Delay_ms(int ms)

{

TIM_SetCounter(TIM2,0);

TIM_Cmd(TIM2,ENABLE);

while(TIM_GetCounter(TIM2)<ms){

}

TIM_Cmd(TIM2,DISABLE);

}

LCD.h

void LCD_CtrlLinesConfig(void);

void LCD_Init(int);

void LCD_clearScreen(int);

void LCD_printString(uint8_t *,int);

void LCD_sendByte(uint8_t, int,int);

LCD.c

#include "stm32f10x.h"

#include "LCD.h"

void LCD_PulseEnablePin(int);

void delayMS(int);

void LCD_sendNibble(uint8_t,int);

void LCD_sendCommand(uint8_t,int);

//void LCD_sendByte(uint8_t, int,int);

int CMD = 0;

int DATA = 1;

void LCD_Init(int chip)

{

delayMS(40);

GPIOC->BSRR = GPIO_Pin_3|GPIO_Pin_2|GPIO_Pin_1|GPIO_Pin_0;

GPIOC->BSRR = GPIO_Pin_13;

GPIOC->BSRR = GPIO_Pin_6;

GPIOC->BSRR = GPIO_Pin_7;

GPIOC->BSRR = GPIO_Pin_5;

GPIOC->BRR = GPIO_Pin_3|GPIO_Pin_2|GPIO_Pin_1|GPIO_Pin_0;

GPIOC->BRR = GPIO_Pin_13;

GPIOC->BRR = GPIO_Pin_6;

GPIOC->BRR = GPIO_Pin_7;

GPIOC->BRR = GPIO_Pin_5;

if (chip == 1){

LCD_sendNibble(0x03,1);

delayMS(5);

LCD_sendNibble(0x03,1);

delayMS(5);

LCD_sendNibble(0x03,1);

delayMS(5);

//set 4bit interface

LCD_sendNibble(0x02,1);

//delayMS(2);

//sending function cmd and two line display

LCD_sendCommand(0x28,1);

delayMS(2);

//sending display cmd,display on and cursor on

LCD_sendCommand(0x0F,1);

delayMS(2);

//sending entry mode cmd and cursor increment

LCD_sendCommand(0x06,1);

//delayMS(1);

//delayMS(1000);

LCD_clearScreen(1);

}

if (chip == 2){

LCD_sendNibble(0x03,2);

delayMS(5);

LCD_sendNibble(0x03,2);

delayMS(5);

LCD_sendNibble(0x03,2);

delayMS(5);

//set 4bit interface

LCD_sendNibble(0x02,2);

//delayMS(2);

//sending function cmd and two line display

LCD_sendCommand(0x28,2);

delayMS(2);

//sending display cmd,display on and cursor on

LCD_sendCommand(0x0F,2);

delayMS(2);

//sending entry mode cmd and cursor increment

LCD_sendCommand(0x06,2);

//delayMS(1);

//delayMS(1000);

LCD_clearScreen(2);

}

void LCD_printString(uint8_t *Str,int chip){

uint8_t *c;

c=Str;

while((c!=0)&& (*c!=0)){

LCD_sendByte(*c,1,chip);

c++;

}

void LCD_setCursorPosition(uint8_t row, uint8_t col,int chip){

uint8_t address;

if (row==0){

address=0;

}else{

address=40;

}

address|=col;

LCD_sendCommand(0x80|address,chip);

}

void LCD_CtrlLinesConfig(void){

GPIO_InitTypeDef GPIO_InitStructure;

/* Enable GPIO clock */

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC,ENABLE);

/* Configure NCS in Output Push-Pull mode -Enable Pin(E1)*/

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13;

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;