AVR - 7seg with button

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

#define CPU_PRESCALE(n) (CLKPR = 0x80, CLKPR = (n))
#define CPU_16MHz       0x00
#define CPU_8MHz        0x01
#define CPU_4MHz        0x02
#define CPU_2MHz        0x03
#define CPU_1MHz        0x04
#define CPU_500kHz      0x05
#define CPU_250kHz      0x06
#define CPU_125kHz      0x07
#define CPU_62kHz       0x08

#define SUCCESS         1
#define ERROR           0

void TWI_init(void)
{
    //set SCL frequency
    TWSR = 0x01;
    TWBR = 0x0C;
    //enable TWI
    TWCR = (1<<TWEN);
}

void TWI_start(void)
{
    TWCR = (1<<TWINT)|(1<<TWSTA)|(1<<TWEN);
    while ((TWCR & (1<<TWINT)) == 0);
}

void TWI_stop(void)
{
    TWCR = (1<<TWINT)|(1<<TWSTO)|(1<<TWEN);
}

void TWI_put_char(uint8_t u8data)
{
    TWDR = u8data;
    TWCR = (1<<TWINT)|(1<<TWEN);
    while ((TWCR & (1<<TWINT)) == 0);
}

uint8_t TWI_get_status(void)
{
    uint8_t status;
    //mask status
    status = TWSR & 0xF8;
    return status;
}

uint8_t serial_7seg_write_char(uint8_t data)
{
    TWI_start();
    if (TWI_get_status() != 0x08)
        return ERROR;
    // send the address
    TWI_put_char(0xE2);
    if (TWI_get_status() != 0x28)
        return ERROR;
    // write one bye
    TWI_put_char(data);
    if (TWI_get_status() != 0x28)
        return ERROR;
    TWI_stop();
    return SUCCESS;
}

uint8_t serial_7seg_move_cursor()
{
    return serial_7seg_write_char(0x79);
}

uint8_t serial_7seg_clear_display()
{
    return serial_7seg_write_char(0x76);
}

int main(void)
{
	// set for 16 MHz clock
	CPU_PRESCALE(CPU_16MHz);

	TWI_init();

	DDRB &= ~(1 << PB7);

	while (1)
	{
        if (PINB & (1<<PB7))
        {
            _delay_ms(100);
            if (PINB & (1<<PB7))
            {
                serial_7seg_write_char('s');
                serial_7seg_write_char('e');
                serial_7seg_write_char('n');
                serial_7seg_write_char('d');
            }
        }
	}
}