¿Se muestran los caracteres de bloque en 16x 2 LCD en lugar de letras al interactuar con atmega328p?

Estoy tratando de mostrar algunos caracteres en 16x2 LCD (1602 A) usando Arduino Uno (atmega328p-pu). He escrito mi código usando C incrustado para el modo de 4 bits. El código está abajo.

#include <avr/io.h>
#include <util/delay.h>

#define LCD_DATA_DDR DDRD
#define LCD_CTRL_DDR DDRB
#define LCD_DataBus PORTD  //Using PD4 to PD7
#define LCD_CTRL_PORT PORTB

//function prototypes
void LCD_Write(unsigned char cmd, unsigned char reg_select);
void LCD_WriteData(char data);
void LCD_WriteCmd(char cmd);
void LCD_Init();

void LCD_Write(unsigned char cmd, unsigned char reg_select)
{
  char  tempCmd;
  if(reg_select == 1)
    LCD_CTRL_PORT |= (1<<PB0);   //Select Data Register
  else
    LCD_CTRL_PORT &= ~(1<<PB0);   //Select Command Register

  //Mask data/cmd
  tempCmd = cmd;
  tempCmd &= 0xf0;// mask Lower 4 bits

  //Set data/cmd
  LCD_DataBus &= 0xf0;           //Set PORTD LSB to HIGH since we use PD4 to PD7
  LCD_DataBus |= tempCmd;        //Set bits in PORTD

  //Send data/cmd
  LCD_CTRL_PORT |= (1<<PB1); // Send a High-to-Low pulse at Enable pin
  _delay_ms(400);
  LCD_CTRL_PORT &= ~(1<<PB1); // Send a High-to-Low pulse at Enable pin

  //******Send next 4bits

  //mask data/cmd
  tempCmd = cmd << 4; //shift left 4 times so the LSB bit can be sent.
  tempCmd &= 0xf0; //mask Lower 4 bits

  //Set data/cmd in bus
  LCD_DataBus &= 0xf0;
  LCD_DataBus |= tempCmd;

  //Send data/cmd
  LCD_CTRL_PORT |= (1<<PB1); // Send a High-to-Low pulse at Enable pin
  _delay_ms(400);
  LCD_CTRL_PORT &= ~(1<<PB1); // Send a High-to-Low pulse at Enable pin

  return ;
}

//Send data by setting RS=1.
void LCD_WriteData(char data)
{
  LCD_Write(data, 1);
}

//Send cmd by setting RS=0.
void LCD_WriteCmd(char cmd)
{
  LCD_Write(cmd, 0);
}

void LCD_Init()
{
    LCD_WriteCmd(0x02); // to initialize LCD in 4-bit mode.
    _delay_ms(1);
    LCD_WriteCmd(0x28); //to initialize LCD in 2 lines, 5X7 dots and 4bit mode.
    _delay_ms(1);
    LCD_WriteCmd(0x01); // clear LCD
    _delay_ms(1);
    LCD_WriteCmd(0x0E); // cursor ON
    _delay_ms(1);
    LCD_WriteCmd(0x80); // —8 go to first line and –0 is for 0th position
    _delay_ms(1);
    return;
}

int main(void)
{
    LCD_DATA_DDR |= 0xf0;  //set the LCD DDRD to output
    LCD_CTRL_DDR |= 0b00000011; //For RS, E

    LCD_Init();
    _delay_ms(30);
    LCD_WriteData('a');
    LCD_WriteData('2');
    while(1)
    {

    }//while
}

Cuando ejecuto este código C, obtengo algunos bloques blancos en la fila superior, en lugar de letras. Luego, ejecuté una versión Arduino del código LCD, pero funcionó bien. Por favor, diga qué me falta en mi código c incrustado.

Estoy usando los siguientes pines para la interfaz LCD,

• D4 a D7 = PD4 a PD7
• RW = conectado a tierra
• RS = PB0
• E = PB1

Gracias.