I put the following code in a at89s8252:

;Serial Interrupt (COMINT.ASM)
;11,059MHz, 1200 Baud
#include 8051.H
.org 0000H
ljmp INIT
.org 0023H
ljmp RX

INIT clr TR1 ;stop timer 1
mov TH1,#0D0H ;256-6: 1200 baud
mov TL1,#0D0H
anl TMOD,#0FH ;Timer1: 8 bit auto-reload
orl TMOD,#20H
setb TR1 ;start timer
mov SCON,#50H ;InitRS232
setb TI
orl PCON,#80H ;SMOD=1
mov IE,#90H ;EA +ES

NEXT nop
nop
sjmp NEXT

RX mov R7,SBUF
dec P1
clr RI
reti

.end

but for some reason, it keeps decreasing P1, even if I don't send characters to the uC? can anybody explain what I do wrong?

Thanks in advance,

Martijn