Dear Friends
Please let know how to use the I2C (TWI) communication for initializing 
micro display during power on.
The Requirement is to initialize the set of 27 registers in OLED Micro 
display (act as slave at address 0x64) when powered ON to enable the 
PAL/NTSC video format.
The details of default set of values are attached in the file. Please 
guide me how to implement using C program for microcontroller 
ATxmega256A3BU.
Datasheet of OLED microdisplay attached.

I have a code as below. Please let me know how to differentiate slave 
address and registers of the slave address and data to be sent.

#include <avr/io.h>
#include "avr_compiler.h"
#include "twi_master_driver.h"
#include "twi_slave_driver.h"

/*! Defining an example slave address. */
#define SLAVE_ADDRESS    0x64

/*! Defining number of bytes in buffer. */
#define NUM_BYTES   27

/*! CPU speed 2MHz, BAUDRATE 100kHz and Baudrate Register Settings */
#define CPU_SPEED   2000000
#define BAUDRATE     100000
#define TWI_BAUDSETTING TWI_BAUD(CPU_SPEED, BAUDRATE)


/* Global variables */
TWI_Master_t twiMaster;    /*!< TWI master module. */
TWI_Slave_t twiSlave;      /*!< TWI slave module. */


/*! Buffer with test data to send.*/
uint8_t sendBuffer[NUM_BYTES] = 
{0x01,0x78,0x38,0x78,0x38,0x78,0x38,0x81,0x39,0x4A,0x10,0x00,0x02,0x00,0 
x80,0xC0,0x1B,0x07,0x00,0x90,0x0f,0xD8,0x0C,0x01,0x80,0x00,0xC0};


void TWIC_SlaveProcessData(void)
{
    uint8_t bufIndex = twiSlave.bytesReceived;
       twiSlave.sendData[bufIndex] = (~twiSlave.receivedData[bufIndex]);
}

int main(void)
{
    uint8_t BufPos = 0;
// Enable internal pull-up on PC0, PC1.. Uncomment if you don't have 
external pullups
              PORTCFG.MPCMASK = 0x03; // Configure several PINxCTRL 
registers at the same time
              PORTC.PIN0CTRL = (PORTC.PIN0CTRL & ~PORT_OPC_gm) | 
PORT_OPC_PULLUP_gc; //Enable pull-up to get a defined level on the 
switches

       /* Initialize TWI master. */
       TWI_MasterInit(&twiMaster,
       &TWIC,
       TWI_MASTER_INTLVL_LO_gc,
       TWI_BAUDSETTING);

       /* Initialize TWI slave. */
       TWI_SlaveInitializeDriver(&twiSlave, &TWIC, 
TWIC_SlaveProcessData);
       TWI_SlaveInitializeModule(&twiSlave,
       SLAVE_ADDRESS,
       TWI_SLAVE_INTLVL_LO_gc);

       /* Enable LO interrupt level. */
       PMIC.CTRL |= PMIC_LOLVLEN_bm;
       sei();

       TWI_MasterWriteRead(&twiMaster,        // Module
       slave_reg[BufPos],                         // slave address
       &sendBuffer[BufPos],                   // What to send
       1,                                    // Write how much
       0);                                   // Read how much

       while (twiMaster.status != TWIM_STATUS_READY) {
              /* Wait until transaction is complete. */
       }

       while(1)
    {
        //TODO:: Please write your application code
    }
}

/*! TWIC Master Interrupt vector. */
ISR(TWIC_TWIM_vect)
{
       TWI_MasterInterruptHandler(&twiMaster);
}

/*! TWIC Slave Interrupt vector. */
ISR(TWIC_TWIS_vect)
{
       TWI_SlaveInterruptHandler(&twiSlave);
}