Ok das hilft mir schon mal weiter. Aber ich bekomme immer Fehlermeldungen beim erstellen meiner Datei.

Code:
>Session Environment Variables:
AF_AVRDIR=C:\WinAVR
AF_PROJECT=test
AF_SOURCE_FILES=test.c i2c.c
AF_ASM_SRC_FILES=
AF_PRGDIR=C:\Programme\AsuroFlash
AF_PRJDIR=C:\AsuroFlash\asuro-lib\examples\US
AF_ASURO_LIB_PATH=C:\AsuroFlash\asuro-lib\lib
File test.c saved.
>Default make_all.cmd file created.
>Default makefile created.
Make
C:\AsuroFlash\asuro-lib\examples\US>C:\WinAVR\utils\bin\make.exe all 
set -e; avr-gcc -MM -mmcu=atmega8 -I. -g -Os -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -Wall -Wstrict-prototypes -Wa,-ahlms=test.lst -IC:\Programme\AsuroFlash\include test.c \
	| sed 's,\(.*\)\.o[ :]*,\1.o \1.d : ,g' > test.d; \
	[ -s test.d ] || rm -f test.d
-------- begin --------
avr-gcc --version
avr-gcc (WinAVR 20090313) 4.3.2
Copyright (C) 2008 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Size before:
test.elf  :
section           size      addr
.text              714         0
.bss                17   8388704
.stab              888         0
.stabstr            95         0
.debug_aranges     128         0
.debug_pubnames    335         0
.debug_info       1165         0
.debug_abbrev      592         0
.debug_line       1025         0
.debug_frame       240         0
.debug_str         502         0
.debug_loc         106         0
Total             5807


avr-gcc -c -mmcu=atmega8 -I. -g -Os -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -Wall -Wstrict-prototypes -Wa,-ahlms=test.lst -IC:\Programme\AsuroFlash\include test.c -o test.o
test.c: In function 'read_pcf8591_adc':
test.c:12: warning: passing argument 1 of 'StartI2C' makes integer from pointer without a cast
test.c:18: warning: passing argument 1 of 'StartI2C' makes integer from pointer without a cast
test.c: In function 'main':
test.c:42: warning: passing argument 1 of 'SerWrite' makes pointer from integer without a cast
avr-gcc -mmcu=atmega8 -I. -g -Os -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -Wall -Wstrict-prototypes -Wa,-ahlms=test.o -IC:\Programme\AsuroFlash\include test.o i2c.o  --output test.elf -Wl,-Map=test.map,--cref -IC:\Programme\AsuroFlash\lib -lm
test.o: In function `read_pcf8591_adc':
C:\AsuroFlash\asuro-lib\examples\US/test.c:17: undefined reference to `Sleep'
test.o: In function `main':
C:\AsuroFlash\asuro-lib\examples\US/test.c:35: undefined reference to `Init'
C:\AsuroFlash\asuro-lib\examples\US/test.c:37: undefined reference to `FrontLED'
C:\AsuroFlash\asuro-lib\examples\US/test.c:42: undefined reference to `SerWrite'
make: *** [test.elf] Error 1

ExitCode 2
>Ready.

Hier mal das Programm. Es soll den Wert von dem ersten Eingang vom PCF8591 über die serielle Schnittstelle senden.
Code:
#include "asuro.h"
#include "i2c.h"
#define pcf8591_address 0x90           // I2C Adresse des PCF8574


//liest einen ADC Wert vom PCF8591
unsigned char read_pcf8591_adc(unsigned char adc)
{
    unsigned char ret;
    unsigned char byte = 0;

    ret = StartI2C(pcf8591_address+WriteI2C);  // Sende Start Condition
    if (ret == 0)

    ret = WriteI2C(adc);                // Senden des Control Bytes startet die A/D Wandlung
      StopI2C();                            // Sende Stop Condition, Bus freigeben
    Sleep(10);                             // Warten bis A/D Wandlung benedet (mind. 90µs)
    ret = StartI2C(pcf8591_address+ReadI2C);  // Sende Start Condition

    if (ret == 0)
    {
       // Mehrmaliges Lesen um alte A/D Werte zu ignorieren
       byte = ReadI2C(1);      // Lese Byte + acknowledge
       byte = ReadI2C(0);      // Lese Byte + no acknowledge
    }
    else ret = 3;
    StopI2C();                           // Sende Stop Condition, Bus freigeben
    return byte;
}

int main(void)                  
{
    unsigned char rled;
    unsigned char port;
    Init();
    InitI2C();
    FrontLED(ON);
    while(1)
    {
    port=0;
    rled = read_pcf8591_adc(port);
    SerWrite(rled,4);
     }
    return 0;
}