The serial communication with my self-made 8031 board works in assembler (beneath) but it does not work properly with C code doing the same. Anyone to know what the problem may be? Thanks NAME SAMPLE DS 10H CSEG AT 0A100h START: MOV SP,#50 ; Oscillator frequency = 11.059 MHz MOV TMOD,#00100000B ;C/T = 0, Mode = 2 MOV TH1,#0FDH SETB TR1 MOV SCON,#01010010B MOV A, #"a" REPEAT: JNB TI,$ CLR TI MOV SBUF,A SJMP REPEAT END