AVR Freaks

Thank you for your answer David.  I will try to study these timing diagrams and report if i succeed.
I bought OLED display here: https://www.aliexpress.com/item/... (sorry for long link ...)
There are pictures of circuit under discription on that webpage if it helps.. =)
 

Sorry i forgot to say that i'm fairly new to programming microcontrollers i know some basics but not much. So for me almost everything will be hard but i will try my best.

Thank you for advice, but i have managed to use my XMEGA256-A3BU to printf on putty interface via USB, write to microSD card, read 1Wire Temperature sensor and blink a LED. I'm doing datalogger for my master thesis and now i have this problem with OLED display that i need to manage... I just don't understand how can i write library on my own (from start), that's why i said i have no bascis, because i think that if i could do that i could say that i know how to program.

Best Regards,
Matjaz

Hello again,

I have modified SSD1306 so that it uses TWI (I2C) communication instead of SPI. I made following changes...

I have changed conf_ssd1306.h,

in ssd1306.h i added

#elif defined(SSD1306_I2C_INTERFACE)
const uint8_t SLAVE = 0x78;
uint8_t addr = 0;
addr |= SLAVE << 1;
TWIE.MASTER.ADDR = addr;
while(!(TWIE.MASTER.STATUS & TWI_MASTER_WIF_bm));
TWIE.MASTER.DATA = command;
while(!(TWIE.MASTER.STATUS & TWI_MASTER_WIF_bm));
TWIE.MASTER.CTRLC = 0x03; // STOP bit
return;

and 

#elif defined(SSD1306_I2C_INTERFACE)
const uint8_t SLAVE = 0x78;
uint8_t addr = 0;
addr |= SLAVE << 1;
TWIE.MASTER.ADDR = addr;
while(!(TWIE.MASTER.STATUS & TWI_MASTER_WIF_bm));
TWIE.MASTER.DATA = data;
while(!(TWIE.MASTER.STATUS & TWI_MASTER_WIF_bm));
TWIE.MASTER.CTRLC = 0x03; // STOP bit
return;

in ssd1306.c i added

#define BAUDRATE 100000L

#elif defined(SSD1306_I2C_INTERFACE)
TWIE.CTRL = 0x00;
TWIE.MASTER.CTRLB = TWI_MASTER_SMEN_bm;
TWIE.MASTER.BAUD = BAUDRATE;
TWIE.MASTER.CTRLA = TWI_MASTER_ENABLE_bm;
TWIE.MASTER.STATUS= TWI_MASTER_BUSSTATE_IDLE_gc;
return;

When i build and upload the code nothing happens, i have PULL-UP resistors on my OLED SS1306 display and i have set SCL and SDA as output. With my oscilloscope probe i get some signals but it seems that my SSD1306 OLED does not initialize correctly and i think the problem is with reset ssd1306_hard_reset(); at the beginning of void ssd1306_init(void) function.

I don't know how to modify the code bellow, because my controller doesn't have RESET pin..

#define ssd1306_reset_clear()    arch_ioport_set_pin_level(UG_2832HSWEG04_RESET, false)
#define ssd1306_reset_set()      arch_ioport_set_pin_level(UG_2832HSWEG04_RESET, true)

Thank you in advance for your time and help.

Best regards,
Matjaz

I found out, that i have to have the line of code in blue color in order to get signal on SDA and SCL pin... But my OLED display still doesn't function...
Anybody have an idea what to check next ?

	sysclk_enable_module(SYSCLK_PORT_E, SYSCLK_TWI);	//Mora bit, ce ne ne daje na izhodu nic
	TWIE.CTRL = 0x00;							//SDA hold time OFF and normal TWI operation with two-pin interface
	TWIE.MASTER.CTRLB = TWI_MASTER_SMEN_bm;
	TWIE.MASTER.BAUD = 0x4b;			//set baudrate (OBVEZNO PREJ KO ENABLAS MASTER mode)
	TWIE.MASTER.CTRLA = TWI_MASTER_ENABLE_bm;	//enable MASTER mode
	TWIE.MASTER.STATUS= TWI_MASTER_BUSSTATE_IDLE_gc;
	delay_ms(10);	

Thank you in advance =) 

Thank you for explanation. First i tried to use it, but then i decided to do it this way because it is more clear to see what i'm doing in code..

I figure it out that i was using wrong SLAVE address, it's not 0x78 but 0x3C.. And now i'm again stuck specifically at this part of code as you see bellow. It looks like i'm calling SLAVE but he isn't responding.. 

#elif defined(SSD1306_I2C_INTERFACE)

	const uint8_t SLAVE = 0x3C;
	uint8_t addr = 0;
	uint8_t control_1 = 0x40; // Co=0, D/C=1

	addr |= SLAVE << 1;

	TWIE.MASTER.ADDR = addr;
	while(!(TWIE.MASTER.STATUS & TWI_MASTER_WIF_bm));
	delay_us(SSD1306_LATENCY); // At least 3us

	TWIE.MASTER.ADDR = control_1;
	while(!(TWIE.MASTER.STATUS & TWI_MASTER_WIF_bm));
	delay_us(SSD1306_LATENCY); // At least 3us

	TWIE.MASTER.DATA = data;
	while(!(TWIE.MASTER.STATUS & TWI_MASTER_WIF_bm));
	delay_us(SSD1306_LATENCY); // At least 3us
	TWIE.MASTER.CTRLC = 0x03; // STOP bit