Вот мой вариант:

void I2C_WriteByte(unsigned char j)
{
register unsigned char i;

for(i=0x80;i;i>>=1)
{
__delay_cycles( T2_TWI );
if(j&i) SDA_PORT|=SDA_MASK;
else SDA_PORT&=~SDA_MASK;
__delay_cycles( T2_TWI );
SCL_PORT|=SCL_MASK;
__delay_cycles( T4_TWI );
SCL_PORT&=~SCL_MASK;
}

SDA_DDR&=~SDA_MASK;
SDA_PORT|=SDA_MASK;
__delay_cycles( T4_TWI );
SCL_PORT|=SCL_MASK;
__delay_cycles( T4_TWI );
}

#define I2C_IsAck (!(SDA_PIN&SDA_MASK))
#define SHT75_DataReady I2C_IsAck

unsigned char I2C_ReadByte(void)
{
register unsigned char i, data=0;

for(i=0;i<8;i++)
{
__delay_cycles( T4_TWI );
SCL_PORT|=SCL_MASK;
__delay_cycles( T4_TWI );
data<<=1;
if(SDA_PIN&SDA_MASK) data|=0x01;
SCL_PORT&=~SCL_MASK;
}


return data;
}

void I2C_Ack(void)
{
SDA_PORT&=~SDA_MASK;
SDA_DDR|=SDA_MASK;
__delay_cycles( T4_TWI );
SCL_PORT|=SCL_MASK;
__delay_cycles( T4_TWI );
SCL_PORT&=~SCL_MASK;
SDA_PORT|=SDA_MASK;
SDA_DDR&=~SDA_MASK;
__delay_cycles( T4_TWI );
}


void SHT75_StartCondition(void)
{
SDA_PORT|=SDA_MASK;
SCL_PORT&=~SCL_MASK;
__delay_cycles( T4_TWI );
SCL_PORT|=SCL_MASK;
__delay_cycles( T4_TWI );
SDA_PORT&=~SDA_MASK;
__delay_cycles( T4_TWI );
SCL_PORT&=~SCL_MASK;
__delay_cycles( T4_TWI );
SCL_PORT|=SCL_MASK;
__delay_cycles( T4_TWI );
SDA_PORT|=SDA_MASK;
__delay_cycles( T4_TWI );
SCL_PORT&=~SCL_MASK;
}


void SHT75_ConnectionReset(void)
{
register unsigned char i;
SDA_DDR|=SDA_MASK;
SDA_PORT|=SDA_MASK;
SCL_PORT&=~SCL_MASK;
__delay_cycles( T4_TWI );
for(i=0;i<9;i++)
{
SCL_PORT|=SCL_MASK;
__delay_cycles( T4_TWI );
SCL_PORT&=~SCL_MASK;
}
SHT75_StartCondition();
}