Hello there! i am writing a program in which i must monitor port P2.0 to be low and execute some sort of code but i also want that when some data is received in SBUF the control should be transfered to the serial interrupt and after serving ISR return to monitor P2.0 to be low . so the problem is that i contineously monitor P2.0 to be low that code works efficiently but it does not call the serial interrupt when data is trasfered to serial port of 8051 the code slice is given below: org 00h jmp main org 23h call serial main: mov tmod,#20h mov th1,#-3 mov scon,#50h setb tr1 jb p2.0,$ ----------- ----------- ----------- Some Code ----------- ----------- ;Serial ISR serial: MOV A,SBUF oneon: cjne A,#'A',last setb P1.0 clr RI reti last: clr RI reti end