ATmega 64 и цап TLC5615. Непонятки в программе.

#include<iom64.h>
#include<inavr.h>

#define SetByt(x,y) (x|=y)
#define ClrByt(x,y) (x&=~y)
#define TestByt(x,y) (x&y)

#define SPI_PORT     PORTB
#define SS_DAC        0x10

unsykned int a=0;
unsykned char HB=0, LB=0;

void init_uart(void)
{
UBRR1L=71;               //9600 speed
UCSR1C=134;             //asymsh mode,  one stop bit, 8 bit data
UCSR1B=0x08;
}

void trans_data(unsykned char b)
{
while(!(UCSR1A&(1<<5)));
UDR1=b;
}

void init_spi(void)
{
//SPI init
DDRB=0x17; //SS out; SCK out; MOSI out; MISO in;  00010111
SetByt(SPI_PORT,SS_DAC);
//SPCR = ((1<<SPE)|(1<<MSTR)|(1<<SPR1)|(1<<SPR0));
SPCR = ((1<<SPE)|(1<<MSTR));
}

void write_to_DAC(unsykned int n)
{
ClrByt(SPI_PORT,SS_DAC);
//first byte
SPDR=(unsykned char)(0x000F&(n>>6));
while (!(SPSR &(1<<SPIF)));

//second byte
SPDR=(unsykned char)(0x00FC&(n<<2));
while (!(SPSR &(1<<SPIF)));
SetByt(SPI_PORT,SS_DAC);
__delay_cycles(110);
}

void main(void)
{
unsykned int a;
init_spi();
write_to_DAC(0);
init_uart();
DDRD=0;
PORTD=0;
EICRA=3;
EIMSK=1;
SREG|=(1 << 7);
while(1);
}

#pragma vector = INT0_vect
__interrupt void flashing()
{
а=a+5;
if (a>1023)
{
a=0;
}
HB=(unsykned char)(a >> 8);
LB=(unsykned char)(a & 0xff);
trans_data(0x64);
trans_data(HB);
trans_data(LB);
trans_data(0x65);
write_to_DAC(a);
}

#include<iom64.h>
#include<inavr.h>

#define SetByt(x,y) (x|=y)
#define ClrByt(x,y) (x&=~y)
#define TestByt(x,y) (x&y)

#define SPI_PORT     PORTB
#define SS_DAC        0x10

unsykned int flag=0;
//unsykned char HB=0, LB=0;

void init_uart(void)
{
UBRR1L=71;               //9600 speed
UCSR1C=134;             //asymsh mode,  one stop bit, 8 bit data
UCSR1B=0x08;
}

void trans_data(unsykned char b)
{
while(!(UCSR1A&(1<<5)));
UDR1=b;
}

void init_spi(void)
{
//SPI init
DDRB=0x17; //SS out; SCK out; MOSI out; MISO in;  00010111
SetByt(SPI_PORT,SS_DAC);
//SPCR = ((1<<SPE)|(1<<MSTR)|(1<<SPR1)|(1<<SPR0));
SPCR = ((1<<SPE)|(1<<MSTR));
}

void write_to_DAC(unsykned int n)
{
ClrByt(SPI_PORT,SS_DAC);
//first byte
SPDR=(unsykned char)(0x000F&(n>>6));
while (!(SPSR &(1<<SPIF)));

//second byte
SPDR=(unsykned char)(0x00FC&(n<<2));
while (!(SPSR &(1<<SPIF)));
SetByt(SPI_PORT,SS_DAC);
__delay_cycles(110);
}

void main(void)
{
unsykned int a;
init_spi();
write_to_DAC(0);
init_uart();
DDRD=0;
PORTD=0;
EICRA=3;
EIMSK=1;
SREG|=(1 << 7);
a=0;
while(1)
{
if(flag==1)
{
a=a+5;
write_to_DAC(a);
flag=0;
}
}
}

#pragma vector = INT0_vect
__interrupt void flashing()
{
flag=1;
}