m1int.asm

8051 Serial Port Routines by Kevin W. Clark

;FILE: M1INT.ASM
;
;THIS PROGRAM RECEIVES A VALUE ENTERING INTO THE SERIAL PORT PIN RXD AND PUTS
;THE DATA OUT TO PORT 1
;
;
;DETAILS:
;
;THE PROGRAM IS DESIGNED TO BE IN A CONTINUOUS NEVER ENDING LOOP UNTIL A BYTE OF DATA HAS BEEN 
;COMPLETELY RECEIVED.  THE LOOP IS EXITED BECAUSE OF THE OCCURANCE OF A SERIAL INTERRUPT.  AFTER
;THE INTERRUPT HAS BEEN SERVICED, THE PROGRAM GOES BACK INTO IT'S ENDLESS LOOP UNTIL ANOTHER 
;INTERRUPT OCCURS
;
;
	PCON EQU 87H 	;DEFINE PCON REGISTER LOCATION
;
	ORG 00H
;
	JMP MAIN
;
	ORG 023H	 ;STARTING ADDRESS OF SERIAL INTERRUPT
	JMP SERIAL_INT
;
MAIN:   MOV SCON, #50H   ;SET UP SERIAL PORT FOR MODE 0 WITH RECEIVE ENABLED
	MOV TMOD, #20H   ;SET UP TIMER 1 AS AUTO-RELOAD 8-BIT TIMER
        MOV TH1, #0DDH   ;BAUD RATE EQUALS 2400 BAUD AT 16MhZ
        MOV PCON, #80H   ;SET THE DOUBLE BAUD RATE BIT 
	MOV IE, #81H
        MOV TCON, #40H   ;START TIMER 1
        CLR RI		 ;ENSURE THAT THE RECEIVE INTERRUPT FLAG IS CLEAR
LOOP:   JMP LOOP	 ;ENDLESS LOOP (UNLESS INTERRUPT OCCURS)
;
SERIAL_INT:              ;SERIAL INTERRUPT ROUTINE
	CLR RI		 ;CLEAR THE RI BIT (SINCE WE KNOW THAT WAS THE BIT THAT CAUSED THE 
;			  INTERUPT)
	MOV P1, SBUF     ;MOVE THE RECEIVED DATA OUT TO PORT ONE 
	RETI		 ;EXIT THE SERIAL INTERRUPT ROUTINE
	END