It is possibile to use SPI ports to generate pixels, it is better but need some code work:

void initPorts()
{
// D2 is output D6 is AIN0, D7 AIN1
PORTB=0x0c; // SS+MOSI, SS(slave select) MUST be kept high
DDRB&=~0x08;
// all B port input
DDRB|=0x04; // SS is active low, but with 1

PORTD=0xff; // all on
DDRD=0; // all D port input
}

void initSPI()
{
//enable the SPI port
// in master mode
// with phase on
SPCR = (1<<SPE) | (1<<MSTR) | (1<<CPHA);
SPSR = 1; // fosc/2 = 8mhz pixel clock
}

DDRB|=0x08; //sink thru PB3/D11 exit from High impedance

for (int x=0;x<NCHARLINE;x++)
{
SPDR = tileset[screen[x]+y*NCHARTABLE];
_delay_loop_1(2); // 2 *(1+2) = 6 cycle at 16 mhz
//while(!(SPSR & (1<<SPIF)));
}
DDRB&=0xf7;

Q&A: ferrara.remove@libero.it