Thanks Jan, for clarifying my doubts of whether TWI is same as I2C.

The sample code provided by Atmel for TWI is not correct as it has skipped sending the memory address where the data to be written/read.

I had tried that the sample code and it's of no use.

Please enclosed my code. It would be great if you guys could assist me in identifying the problem with my code.


#include<at89c5131.h>
#include<stdio.h>
#include<keyscan.h>

#define I2C_IDLE 0x00
#define I2C_BUSY 0x01
#define I2C_BUSYTX 0x03
#define I2C_BUSYRX 0x05
#define I2C_OK 0x02
#define I2C_ERROR 0x04
#define ACK 0x00 // ACK Signal
#define NACK 0x01 // NACK Signal

sbit bk_lit = P2^2;
sbit latch_en = P3^3; //active low signal
sbit RS = P3^4;
sbit lcd_en = P3^5;

bit err;
bit b_TWI_busy=0;

unsigned char dt[6];
unsigned char i=0;
unsigned char rw; /* 0=write, 1=read */
unsigned char mi2cstatus,mslaveaddress;
unsigned int mbytenum;

sbit led1 = P2^0;
sbit led2 = P2^1;

/***************************************************************************************************************/
void it_TWI(void) interrupt 8 using 1
{
switch(SSCS) /* TWI status tasking */
{
case(0x00): /* A start condition has been sent */
/* SLR+R/W are transmitted, ACK bit received*/
b_TWI_busy=0; /* TWI is free */
break;

case(0x08): /* A start condition has been sent */
case(0x10):
SSDAT = mslaveaddress; /* send slave adress and read/write bit */
SSCON &= 0x0DF; /* clear start condition */
SSCON &= 0x0EF;
mbytenum=0;
break;

case(0x18):
/* SLR+W was transmitted, ACK bit received */
//SSDAT = i2c_master_getbyte(mbytenum);
//i2c_master_getbyte(mbytenum); /* Transmit data byte, ACK bit received */
SSDAT = 0x00;
SSCON &= 0x0DF;
SSCON &= 0x0EF;
break;

case(0x20):
SSCON &= 0x0DF; /* SLR+W was transmitted, NOT ACK bit received */
SSCON |= 0x10; /* Transmit STOP */
b_TWI_busy=0; /* TWI is free */
mi2cstatus = I2C_ERROR;
break;

case(0x28):
if(mbytenum ==4)
{
SSCON &= 0x0EF;
SSCON |=0x10;
mi2cstatus = I2C_OK;
led1=1;
//b_TWI_busy=0;
//mbytenum=0;
}
else
{
mbytenum++;
SSDAT =i2c_master_getbyte(mbytenum); //i2c_master_getbyte(mbytenum);

SSCON &= 0x0DF;
SSCON &= 0x0EF;
}
break;

case(0x30):
SSCON &= 0x0DF; // DATA was transmitted,NOT ACK bit received
SSCON |= 0x10; //Transmit STOP
b_TWI_busy=0; // TWI is free
mi2cstatus = I2C_ERROR;
break;


case(0x38): // Arbitration lost in SLA+W or DATA.
SSCON |= 0x20;
SSCON &= 0x0EF;
b_TWI_busy=0; // TWI is free
//wr_lcd_dw(0x67);
break;

}
SSCON &= 0xF7; // clear flag

}

//*************************************************************************************
void main()
{
led1=led2=0;
init_lcd();
init_i2c();
bk_lit=0;
mbytenum=0;
mslaveaddress=0x0A0; // slave adresse example
EA=1; // interrupt enable
while(1)
{
if(!b_TWI_busy && ((SSCON&0x10)!=0x10)) // if the TWI is free
{
b_TWI_busy=1; // flag busy =1
rw=0; // 0=write
SSDAT = 0x00; // clear buffer before sending data
SSCON |= 0x20; // TWI start sending
}
}
}
/***************************************************************************************************************/
void init_lcd()
{

wr_lcd_cw(0x30);
wr_lcd_cw(0x30);
wr_lcd_cw(0x30);
// 0 0 1 DL N F 0 0 DL=1 8 bit inetrface
// N = 1 no. of lines 'two'
// F = 0 font size 5x7
wr_lcd_cw(0x38);
//0 0 0 1 S/C R/L 0 0 S/C = 0 Cursor on
// R/L = 1 Shift one space right
wr_lcd_cw(0x14);
//0 0 0 0 1 D C B D = 1 screen on
// C = 1 cursor on
// B = 1 blink on
wr_lcd_cw(0x0F);
//0 0 0 0 0 1 I/O S I/O = 1 cursor moves right
// S =0 shift cursor
wr_lcd_cw(0x06);
//0 0 0 0 0 0 1 0 clear and home cursor
wr_lcd_cw(0x01);

delay_ms(50);
}

//--------------------- delay------------------------------------------------
void delay(unsigned char dly)
{
for(;dly!=0;dly--);
}

void delay_ms(unsigned char dly_ms)
{
for(;dly_ms!=0;dly_ms--)
delay(100);
}

//------------------function to write commands to LCD-------------------------
void wr_lcd_cw(unsigned char cmd)
{
P0=cmd;
RS = 0; //send command
toggle_e();
}
//------------------function to enable LCD-------------------------------------
void toggle_e()
{
latch_en = 0; //enable latch
lcd_en = 1;
delay_ms(50);
lcd_en = 0;
latch_en=1; //disable latch
}
//----------------function to write Data to LCD----------------------------------

void wr_lcd_dw(unsigned char dta)
{
P0 = dta;
RS = 1; // send data
toggle_e();
}
/************************************************************************
DESC: gets the next byte to be transmitted when operating as
a master
RETURNS: byte to transmit
************************************************************************/
unsigned char i2c_master_getbyte(unsigned int bytenum)
{

unsigned char array[5]={0x66,0x67,0x68,0x69,0x6A};
return (array[bytenum]);
}


//***********************************************************************
void init_i2c()
{
P4_1 =1;
P4_0 =1;

SSCON = 0xC2; // enable TWI interrupt

IPH1 = 0x02;
IPL1 = 0x02;

IEN1 = 0x02;

mi2cstatus = I2C_IDLE;
}