I have a sub void init() { PCON |= 0x80; TMOD |= 0x20; SCON=0x52; TH1=0xF3; TR1=1 } void main() { init(); while(1) { } } I see no reason why when I call init() it automatic send two bytes to my PC because I run my program on PC it receives "||" or "o'".Could someone help me to solve this problem? Thanks.