LCD und I2C

[Paulchen 999]

Hallo
Versuche das Display von Pollin mit dem I2C Adapter in Betrieb zu nehmen. Habe bisher den folgenden Code:

#define F_CPU 16000000UL
#include "i2cmaster.h"
#include <util/delay.h>
#include "lcd.h"

#include "i2clcd.h"

#define LCD_I2C_ADDRESS    0x40		// Adresse I2C

#define ENABLE_MASK      0b01000000
#define DISABLE_MASK    0b10111111
#define COMMAND_MASK    0b00000000
#define DATA_MASK      0b00100000

#define INIT_4BIT_MODE    0b00000010

void write_to_pcf8574(char data)
{
	i2c_write(data);
	_delay_us(40);
	i2c_write(data | ENABLE_MASK);
	_delay_us(40);
	i2c_write(data & DISABLE_MASK);
	_delay_us(40);
}

void write_byte(char data, char mask)
{
	//write the high nibble first...
	char nibble = mask | ((data & 0xF0) >> 4);
	write_to_pcf8574(nibble);
	
	//...then the low nibble
	nibble = mask | (data & 0x0F);
	write_to_pcf8574(nibble);
}

void write_command(char data)
{
	write_byte(data, COMMAND_MASK);
}

void write_data(char data)
{
	write_byte(data, DATA_MASK);
}

void write_string(char string)
{
	while (string)
	{
		write_data(string);
		string++;
	}
}

void init_display()
{
	//turn on 4 bit mode
	write_to_pcf8574(INIT_4BIT_MODE);
	write_command(0x28);
	_delay_ms(50);
	write_command(0x0c);
	_delay_ms(50);
	write_command(0x06);
	_delay_ms(50);
	write_command(0x01);
	_delay_ms(50);
	write_command(0x0f);
	_delay_ms(50);
}

int main()
{
	lcd_init();
	i2c_init();
	i2c_start_wait(LCD_I2C_ADDRESS + I2C_WRITE);
	write_string("Hello World");
	i2c_stop();
	return 0;
}

Arbeite mit einem ATmega 32, 16 MHz, AVR Studio 6, PCF8574 Adresse 0x40. Die Datein habe ich eingebunden
Bekomme die folgenden Fehlermeldungen. Leider konnte ich diese nicht zuordnen:

Warning 2 declared here
Warning 4 expected 'char' but argument is of type 'char *'
Warning 3 passing argument 1 of 'write_string' makes integer from pointer without a cast [enabled by default]
Error 1 too few arguments to function 'lcd_init'