after linking my code I get: *** ERROR L121: IMPROPER FIXUP MODULE: prog_fsk.obj (PROG_FSK) SEGMENT: ABSOLUTE Everything was OK before untill the moment, when I changed one of my program functions to be ISR. Here is it's source code: void CallerId(void) interrupt 0 using 2 { char c; int timeout=0; char i; //licznik petli while(P3_2==0); //czeka az skonczy sie pierwszy dzwonek P3_3=0; //przelaczenie CMX 612 w tryb odbioru danych FSK P3_7=1; c=_getkey(); while(c!=0x55) //czekamy na blok Chan Seize (ASCII 'U') { c=_getkey(); //czym rozni sie getkey od getchar???? timeout++; if(timeout==10000) //aktywowac przerwanie INT 1 tylko po co????????? {dzwonek=0; return; //nieudana transmisja danych } } timeout=0; while(c!=0x80) //czekamy na naglowek CLIP (call setup) { c=_getkey(); timeout++; if(timeout==10000) { //aktywowac przerwanie INT 1 tylko po co????????? dzwonek=0; return; //nieudana transmisja danych } } fsk_tab[0]=c; //"call setup" c=_getkey(); fsk_tab[1]=c; //liczba bajtow wiadomosci (nie liczac pol "call setup" i "Message Lenght") for(i=2;i<c+2;i++) { fsk_tab[i]=_getkey(); } P3_3=1; //przelaczenie CMX 612 w tryb "Zero Power" P3_7=0; dzwonek=1; } and here memory map: LINK MAP OF MODULE: prog_fsk (PROG_FSK) TYPE BASE LENGTH RELOCATION SEGMENT NAME ----------------------------------------------------- * * * * * * * D A T A M E M O R Y * * * * * * * REG 0000H 0008H ABSOLUTE "REG BANK 0" DATA 0008H 0006H UNIT _DATA_GROUP_ 000EH 0002H *** GAP *** REG 0010H 0008H ABSOLUTE "REG BANK 2" DATA 0018H 0050H UNIT ?DT?PROG_FSK IDATA 0068H 0001H UNIT ?STACK * * * * * * * C O D E M E M O R Y * * * * * * * CODE 0000H 0003H ABSOLUTE CODE 0003H 0002H ABSOLUTE 0005H 07FBH *** GAP *** CODE 0800H 00F6H UNIT ?C?LIB_CODE CODE 08F6H 00D9H INBLOCK ?PR?MAIN?PROG_FSK CODE 09CFH 00B4H INBLOCK ?PR?CALLERID?PROG_FSK CODE 0A83H 008CH UNIT ?C_C51STARTUP CODE 0B0FH 0086H INBLOCK ?PR?PRINTCLIP?PROG_FSK CODE 0B95H 005CH INBLOCK ?PR?SAVECLIP?PROG_FSK CODE 0BF1H 004DH INBLOCK ?PR?_PRINTWPIS?PROG_FSK CODE 0C3EH 002DH INBLOCK ?PR?_CHECKSUM?PROG_FSK CODE 0C6BH 001CH INBLOCK ?PR?_WRITE_DATA?PROG_FSK CODE 0C87H 0014H INBLOCK ?PR?SERIAL_INIT?PROG_FSK CODE 0C9BH 000FH INBLOCK ?PR?_WRITE_CMD?PROG_FSK CODE 0CAAH 000EH INBLOCK ?PR?_WRITE_NIBBLE?PROG_FSK CODE 0CB8H 000CH INBLOCK ?PR?LCD_INIT?PROG_FSK CODE 0CC4H 000AH UNIT ?PR?_GETKEY?_GETKEY CODE 0CCEH 0004H UNIT ?C_INITSEG Thank you for help, Wojtek PS I'm using Keil Evaluation Project settings: -Device: