Code:
org 0                                       ;  Starting from 0  code memory location 
mov p1, #00                             ;  All LEDs OFF by default
mov tmod, #20h                        ; Timer 1 mode 2, 8 bit auto relaod for serial communication
mov th1, #-3                             ; Set the baud rate
mov scon, #50h                        ; configure the UART, mode selection, 8 bit data, one stop bit, no parity, and receiver is enabled
setb tr1                                    ; start timer 1
wait:jnb ri, wait                          ; receiver interrupt, wait until unles a character from PC is received
mov a, sbuf                               ; once character is received by SBUF register it will be shifted to Register A
mov p1, a                                 ; send the received code to port 1 (LEDs)
clr ri                                         ;  RI receive interrupt which is raised(HIGH) is now cleared so that new data will be
sjmp wait
end