msp430 i2c problems

Can you measure the SDA/SCL lines with an oscilloscope or logic analyzer? Or at least a multimeter?

Yes, I've checked with multimeter

General Voltage 3.7V

and both sda and scl 3.7V

You cannot simply send characters over I²C; you have to send command and data bytes to the HD44780 using the correct protocol, and to configure it first. Even Wikipedia explains it.

"\x24" is the fourth byte, "8" the fifth.

With the I/O expander, you have only 8 bits.

To write to the LCD controller, you have to first set the data bits and RS/RW bits to their desired values, and E to 1, and then you have set E to 0. (It is the falling edge of E that causes the controller to act on its inputs.)

To write a byte, you have to write 4 bits, twice. (Except at the beginning, where you are in 8-bit mode.)

To write a command byte with bits HGFEDCBA, you have to write HGFE0100, HGFE0000, DCBA0100, DCBA0000.
To write a data byte with bits HGFEDCBA, you have to write HGFE0101, HGFE0001, DCBA0101, DCBA0001.

When you send a byte over I²C, you set the outputs of the PCF8574. In every sent byte, the bits are D7 D6 D5 D4 0 E RW RS.

SMCLK and UCBxBR set the speed of the I²C communication; this has nothing to do with the interface between the PCF and the HD. UCTR specifies that you're transmitting on the I²C bus; this has nothing to do with the RW bit.

To set E, send a byte with the value xxxxx1xx. To clear E, send a byte with the value xxxxx0xx. Similarly for all the other bits.

You need helper functions like this:

void switchFrom8To4Bits()
{
	static unsigned char buf[2] = { 0x24, 0x20 };

	dataTransmit = buf;
	size = 2;
	while(UCB0STAT & UCBBUSY);
	UCB0CTL1 |= UCTR + UCTXSTT;
}

void write2x4Bits(unsigned char bits, int is_data)
{
	static unsigned char buf[4];

	buf[0] = (bits & 0xf0) | is_data | 0x04;
	buf[1] = (bits & 0xf0) | is_data;
	bits <<= 4;
	buf[2] = (bits & 0xf0) | is_data | 0x04;
	buf[3] = (bits & 0xf0) | is_data;

	dataTransmit = buf;
	size = 4;
	while(UCB0STAT & UCBBUSY);
	UCB0CTL1 |= UCTR + UCTXSTT;
}

void writeCommand(unsigned char command)
{
	write2x4Bits(command, 0);
}

void writeData(unsigned char data)
{
	write2x4Bits(command, 1);
}

when i use switchFrom8To4Bits the lcd stop reacting i mean when i send 0x24 and then 0x20 but sending only 0x20 it doesn't get stuck just does nothing

here's the code with the new functions you gave me:

#include <msp430.h> 

/*
 * main.c
 */
signed char size;
unsigned char *dataReceive;
unsigned char *dataTransmit;

unsigned char slaveAddr = 0X27;

void switchFrom8To4Bits()
{
    static unsigned char buf[2] = { 0x24, 0x20 };

    dataTransmit = buf;
    size = 2;
    while(UCB0STAT & UCBBUSY);
    UCB0CTL1 |= UCTR + UCTXSTT;
}


void write2x4Bits(unsigned char bits, int is_data)
{
    static unsigned char buf[4];

    buf[0] = (bits & 0xf0) | is_data | 0x04;
    buf[1] = (bits & 0xf0) | is_data;
    bits <<= 4;
    buf[2] = (bits & 0xf0) | is_data | 0x04;
    buf[3] = (bits & 0xf0) | is_data;

    dataTransmit = buf;
    size = 4;
    while(UCB0STAT & UCBBUSY);
    UCB0CTL1 |= UCTR + UCTXSTT;
}

void writeCommand(unsigned char command)
{
    write2x4Bits(command, 0);
}

void writeData(unsigned char data)
{
    write2x4Bits(data, 1);
}

int main(void) {
    WDTCTL = WDTPW | WDTHOLD;	// Stop watchdog timer
	P1SEL |= BIT7 + BIT6; // SET SDA + SCL Functions
	P1SEL2 |= BIT7 + BIT6; // SET SDA + SCL Functions
	UCB0CTL1 |= UCSWRST; //reset
	UCB0CTL0 |= UCMST + UCMODE_3 + UCSYNC; // I2C SYNC MASTER MODE 10 BIT ADDRESS
	UCB0BR0  = 0x08;
	UCB0BR1  = 0;
	UCB0I2CSA = slaveAddr;
	UCB0CTL1 |= UCSSEL_3 + UCSWRST; // SMCLK
	UCB0CTL1 &= ~UCSWRST; //resume operation
	UCB0I2CIE |= UCNACKIE;
	IE2 |= UCB0TXIE + UCB0RXIE;                      // Enable TX & RX interrupt

	__bis_SR_register(GIE);

	switchFrom8To4Bits();
	writeCommand(0x04);
	writeCommand(0x00);
	writeData(0x55);
	writeData(0x81);
	/*dataTransmit ="\x04\x00\x55\x81";//"H";
	size = 4;
	while(UCB0STAT & UCBBUSY);//waiting for master stop being busy
		UCB0CTL1 |= UCTR + UCTXSTT ; // set transmitter and start condition
	__bis_SR_register(GIE);*/
	while(1){
	}
	return 0;
}


#pragma vector = USCIAB0RX_VECTOR
__interrupt void USCIAB0RX_ISR(void)
{
  if (UCB0STAT & UCNACKIFG){            // send STOP if slave sends NACK
    UCB0CTL1 |= UCTXSTP;
    UCB0STAT &= ~UCNACKIFG;
  }


}

#pragma vector = USCIAB0TX_VECTOR
__interrupt void USCIAB0TX_ISR(void)
{
  if (IFG2 & UCB0RXIFG){
    if ( size == 0 ){
      UCB0CTL1 |= UCTXSTP;                    // I2C stop condition
      *dataReceive = UCB0RXBUF;
      dataReceive++;
    }
    else {
      *dataReceive = UCB0RXBUF;
      dataReceive++;
      size--;
    }
  }
  else if (IFG2 & UCB0TXIFG){
    if (size == 0){
      UCB0CTL1 |= UCTXSTP;                    // I2C stop condition
      IFG2 &= ~UCB0TXIFG;                     // Clear USCI_B0 TX int flag
    }
    else {
      UCB0TXBUF = *dataTransmit;
      _delay_cycles(250000);
      dataTransmit++;
      size--;
    }
  }
}

    writeCommand(0x04);
    writeCommand(0x00);

Command 0x04 (decrement, no shift) does not make sense, and there is no command 0x00.

You forgot to switch on the display.

to show the display i need 2 lines of command one for the higher 4 bits and the second for the lower 4 bits in which the E is changed (first with 1 the second with 0)

the higher fout bits are 0000 (db4-db7) and the lower bits are 1111 (because  i want to display to be on and to see cursor and the cursor blinks)

so the first command will be: 00000100 (0x04) 

the second  will be: 11110000(0xf0)

so i added: 

writeCommand(0x04);
writeCommand(0xF0);

but is not working this is what happens when i ran the  new code

Resetting the MSP does not reset the HD44780; to reliably initialize 4-bit mode, you need something like this:

void switchFrom8To4Bits()
{
    static unsigned char buf[8] = { 0x34, 0x30, 0x34, 0x30, 0x34, 0x30, 0x24, 0x20 };

    dataTransmit = buf;
    size = 8;
    while(UCB0STAT & UCBBUSY);
    UCB0CTL1 |= UCTR + UCTXSTT;
}

To initialize the LCD, you should use these commands:

sendCommand(0x2F); // function set: 4-bit mode, 2 lines, 5x10 characters
sendCommand(0x0F); // display on
sendCommand(0x01); // display clear
sendCommand(0x06); // entry mode

yes you right now it's working perfectly

YOU ARE THE MAN (yes i'm shouting because i'm excited)

thank you so much very so much