Lcd 4 bit initialization problem after MCU reset

[Vindhyachal.takniki]

1. I have interfaced 16x2 lcd in 4 bit mode. D0-D3 & R/w of lcd are grounded.

2. If system is power on, then lcd works properly. No issue. I have tried many times.

3. But when I press reset button on MCU so that it get reset & reinit the lcd. It don't works most of the time.
I don't understand why. Sometimes some random chinese number, some cursor only & sometimes random numbers.


4. All other pins interfaced worked fine when MCU get reset like led's & adc module except lcd.

5. Below is my code for lcd.

Code: [Select]

void main(void)
{
    const uint8_t str1[] = "******";
    const uint8_t str2[] = "999999";

    configure_lcd();
    lcd_string_print(&str1[0] , 0x80U);
    lcd_string_print(&str2[0] , 0xc0U);   
   
    while(1);
}



void configure_lcd(void) 
{
    initialize_lcd_pins();  
    init_lcd();
   
} 


void lcd_string_print(const uint8_t *p_str , uint8_t address) 
{ 
    uint8_t cnt = 0U;        /* max 16 chars to be printed */
    write_lcd_command(address);
    while( (*p_str != '\0') && (cnt < 16U) )
    {
        write_lcd_data(*p_str);
        p_str++;
    }
   
} 




void write_lcd_data(uint8_t value) 
{ 
    uint8_t cnt;
    LCD_RS_HIGH();
   
    shift_data_on_lcd_pins(value & 0xf0U);
    toggle_lcd_en_pin();
   
/* delay for 12ms */  
    __delay_us(12000);

    shift_data_on_lcd_pins( (value << 4U) & 0xf0U );
    toggle_lcd_en_pin( );    
   
/* delay for 12ms */  
    __delay_us(12000);      
   
} 




void write_lcd_command(uint8_t value) 
{ 
    uint8_t cnt;  
    LCD_RS_LOW();
   
    shift_data_on_lcd_pins(value & 0xf0U);
    toggle_lcd_en_pin();
   
/* delay for 12ms */  
    __delay_us(12000);    
   
    shift_data_on_lcd_pins( (value << 4U) & 0xf0U );
    toggle_lcd_en_pin( );    
   
/* delay for 12ms */  
    __delay_us(12000);    
   
}



static void init_lcd(void) 
{ 
    uint8_t cnt;
/* delay for 300ms */  
    __delay_ms(300);    
   
/* rs shoud be low */    
    LCD_RS_LOW();
   
/* write 0x30 on port */    
    shift_data_on_lcd_pins(0x30U);
    __delay_us(12000); 
   
/* write 0x30 on port */    
    shift_data_on_lcd_pins(0x30U);    
    __delay_us(12000);      

/* write 0x30 on port */    
    shift_data_on_lcd_pins(0x30U);      
    __delay_us(12000); 
   
/* write 0x20 on port */    
    shift_data_on_lcd_pins(0x20U);      
    toggle_lcd_en_pin();    
   
    write_lcd_command(0x28U);
    __delay_us(12000);    
   
    write_lcd_command(0x0cU);
    __delay_us(12000); 
   
    write_lcd_command(0x01U); 
    __delay_us(12000); 
   
    write_lcd_command(0x06U);
    __delay_us(12000); 
   
    write_lcd_command(0x80U);
    __delay_us(12000);    
   
    write_lcd_command(0x0eU);
    __delay_us(12000);      
   
} 




static void shift_data_on_lcd_pins(uint8_t value) 
{ 
    if(value & REG8_BIT_7)
    {
        LCD_D7_HIGH();
    }  
    else
    {
        LCD_D7_LOW();
    }  
   
   
    if(value & REG8_BIT_6)
    {
        LCD_D6_HIGH();
    }  
    else
    {
        LCD_D6_LOW();
    }      
   
   
    if(value & REG8_BIT_5)
    {
        LCD_D5_HIGH();
    }  
    else
    {
        LCD_D5_LOW();
    }      
   
   
    if(value & REG8_BIT_4)
    {
        LCD_D4_HIGH();
    }  
    else
    {
        LCD_D4_LOW();
    }        
   
} 


void initialize_lcd_pins(void) 
{ 
    LCD_EN_OUTPUT_LOW();
    LCD_RS_OUTPUT_LOW();  
    LCD_D7_OUTPUT_LOW();
    LCD_D6_OUTPUT_LOW();  
    LCD_D5_OUTPUT_LOW();
    LCD_D4_OUTPUT_LOW();      
   
} 



static void toggle_lcd_en_pin(void) 
{ 
    LCD_EN_HIGH();
    __delay_us(500);
    LCD_EN_LOW();
    __delay_us(500);
   
}  

[alank2]

D0-D3 should be left disconnected per the datasheet...

[Rufus]

The 0x30s sent to set 4 bit mode are not being strobed into the LCD.

[Ansel]

Below is my code for lcd.
But when I press reset button on MCU so that it get reset & reinit the lcd. It don't works most of the time.
I don't understand why. Sometimes some random chinese number, some cursor only & sometimes random numbers.
If system is power on, then lcd works properly. No issue. I have tried many times.
I have interfaced 16x2 lcd in 4 bit mode. D0-D3 & R/w of lcd are grounded.
All other pins interfaced worked fine when MCU get reset like led's & adc module except lcd.



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[lapm]

Read datasheet of display very very carefully... Some displays needs to initialized to 4 bit mode twice... had few of 1x16 displays that require this...

[Rufus]

Read datasheet of display very very carefully... Some displays needs to initialized to 4 bit mode twice... had few of 1x16 displays that require this...

You need to write 8 bit mode 3 times. If the display is 'on' the second half of a 4 bit transfer the first write will be lost, if the display is in 4 bit mode it takes two writes to set 8 bit mode. If the display is in 8 bit mode you just set it again 3 times.

After writing 8 bit mode 3 times with the appropriate delays you are sure it is in 8 bit mode and can then set it to 4 bit mode. I have never seen a requirement to set 4 bit mode twice.

[Vindhyachal.takniki]

Tomorrow I will try to init the lcd twice to see if that works

[mikerj]

Tomorrow I will try to init the lcd twice to see if that works

But take note of what Rufus said in his first post!  In init_lcd() you set 0x30 on the LCD data pins three times, but you never toggle the Enable pin so this won't be doing anything.

[Vindhyachal.takniki]

Thanks @Rufus, problem solved.
Lcd is working fine after reset