This is just the sparkfun example code that I modified for an ATmega8.
Parallel 8080 mode.
Since it may be useful, I’ve decided to post it 
/*
* Mcu type: ATmega8
* Fuses: Default fuses (1MHz internal osc)
* Hardware connection:
* D0 -> PB0
* D1 -> PB1
* ...
* D7 -> PB7
*
* RES -> PC0
* CS -> PC1
* DC -> PC2
* E(RD) -> PC3
* RW(WR) -> PC4
* EN -> PC5
*(Not strictly necessary) Connect a led to PD0
*
*/
#define F_CPU 1000000
#include <inttypes.h>
#include <avr/io.h>
#include <stdlib.h>
#include <util/delay.h>
// inialize OLED
void OLED_init(void);
// reset Controller
void Reset_SSD1339(void);
// write command or data
void write_c(unsigned char out_command);
void write_d(unsigned char out_data);
// these write data to the OLED on 8 bit data bus, depends on MCU
void LCD_out(unsigned char cmd);
unsigned int get_LCD_port(unsigned char data);
// these functions set / clear pins for OLED control lines. they accecpt a 0 or 1
void RD(char stat);
void RW(char stat);
void DC(char stat);
void RES(char stat);
void CS(char stat);
#define X_OFFSET 0
#define Y_OFFSET 0
void line(uint8_t x1,uint8_t y1,uint8_t x2,uint8_t y2)
{
write_c(0x83);//Draw line
write_d(X_OFFSET+x1);
write_d(Y_OFFSET+y1);
write_d(X_OFFSET+x2);
write_d(Y_OFFSET+y2);
write_d(7);//Color green
write_d(224);
_delay_ms(10);
}
void long_delay()
{
uint8_t i;
for(i=0;i<20;i++) _delay_ms(100);
}
void ioinit()
{
PORTB=0;
DDRB=0xFF;//PortB 0..7:Data bus (Out)
PORTC=31;//'00011111' EN @ 0 (dc-dc off)
DDRC=63;//'00111111' Pc0=RES Pc1=CS Pc2=D/C Pc3=RD Pc4=WR Pc5=EN
PORTD=0xFF;
DDRD=1;//Pd0=Led
}
int main()
{
int i=0;
ioinit();
OLED_init();
_delay_ms(120);
write_c(0x8e); // clear window command
write_d(0);
write_d(0);
write_d(130);
write_d(130);
long_delay();
write_c(0x92); // fill enable command
write_d(0x01);
_delay_ms(10);
// draw 100 random circles
for(i = 0;i < 100;i++){
write_c(0x86); // draw circle command
write_d(rand() % 130);
write_d(rand() % 130);
write_d(rand() % 64);
write_d(rand());
write_d(rand());
write_d(rand());
write_d(rand());
_delay_ms(10);
}
long_delay();
write_c(0x8e); // clear window command
write_d(0);
write_d(0);
write_d(130);
write_d(130);
_delay_ms(100);
// write directly to ram, this fills up bottom 1/3 of display with color pattern
write_c(0x5c);
for (i = 0; i < 2000; i++){
write_c(0x5c);
write_d(i);
write_d(i);
write_d(i);
_delay_ms(1);
}
long_delay();
write_c(0x8e); // clear window command
write_d(0);
write_d(0);
write_d(130);
write_d(130);
_delay_ms(100);
line(0,0,127,127);//Draw lines
line(0,0,10,0);
line(0,0,0,10);
line(127,127,117,127);
line(127,117,127,127);
for(;;)//Blink LED
{
PORTD|=_BV(0);
_delay_ms(100);
PORTD&=~_BV(0);
_delay_ms(100);
}
}
/**********************************************************
Initialize
***********************************************************/
void OLED_init(void)
{
PORTC|=_BV(5);//EN High (DC-DC ON)
//LCD_out(0);
//RD(1);
//DC(0);
//RW(0);
//CS(0);
Reset_SSD1339();
write_c(0xa0); // Set Re-map / Color Depth
write_d(0x34);//0xb4); // 262K 8bit R->G->B (0x34=256color 0xb4=262Kcolor)
write_c(0xa1); // Set display start line
write_d(0x00); // 00h start
write_c(0xa2); // Set display offset
write_d(0x80); // 80h start
write_c(0xA6); // Normal display
write_c(0xad); // Set Master Configuration
write_d(0x8e); // DC-DC off & external VcomH voltage & internal pre-charge voltage
write_c(0xb0); // Power saving mode
write_d(0x05);//
write_c(0xb1); // Set pre & dis_charge
write_d(0x11); // pre=1h dis=1h
write_c(0xb3); // clock & frequency
write_d(0xf0); // clock=Divser+1 frequency=fh
write_c(0xbb); // Set pre-charge voltage of color A B C
write_d(0x1c); // color A
write_d(0x1c); // color B
write_d(0x1c); // color C
write_c(0xbe); // Set VcomH
write_d(0x1f); //
write_c(0xc1); // Set contrast current for A B C
write_d(0xaa); // Color A
write_d(0xb4); // Color B
write_d(0xc8); // Color C
write_c(0xc7); // Set master contrast
write_d(0x0f); // no change
write_c(0xca); // Duty
write_d(0x7f); // 127+1
write_c(0xaf); // Display on
}
void Reset_SSD1339(void)
{
RES(0);
_delay_ms(100);
RES(1);
}
void write_c(unsigned char out_command)
{
LCD_out(out_command);
DC(0);CS(0);RW(0);
_delay_us(50);
RW(1);
CS(1);
DC(1);
}
void write_d(unsigned char out_data)
{
LCD_out(out_data);
DC(1);CS(0);RW(0);
_delay_us(50);
RW(1);
CS(1);
DC(1);
}
// these functions set / clear pins for LCD control lines. they accecpt a 0 or 1
void RD(char stat)
{
if (stat==1) PORTC|=_BV(3);//Pc3= RD
else PORTC&=~_BV(3);
}
void RW(char stat)
{
if (stat==1) PORTC|=_BV(4);//Pc4= RW
else PORTC&=~_BV(4);
}
void DC(char stat)
{
if (stat==1) PORTC|=_BV(2);//Pc2= DC
else PORTC&=~_BV(2);
}
void RES(char stat)
{
if (stat==1) PORTC|=_BV(0);//Pc0= RES
else PORTC&=~_BV(0);
}
void CS(char stat)
{
if (stat==1) PORTC|=_BV(1);//Pc1= CS
else PORTC&=~_BV(1);
}
// send to the LCD
void LCD_out(unsigned char cmd)
{
PORTB=cmd;
}
