di2730.txt
;***************************************************************************************************
; LISTING 1 - FIVE-PRIORITY-LEVEL INTERRUPT SYSTEM FOR 8051P
;
; "Software makes full use of 8051's interrupt system," EDN, Dec 6, 2001, pg 111.
;
;***************************************************************************************************



	ORG	0000H
	LJMP	START
	ORG	0003H
	LJMP	INT0
ORG	000BH
	LJMP	IT0
ORG	0013H
	LJMP	INT1
ORG	001BH
LJMP	IT1
ORG	0023H
	LJMP	INTP
START:	MOV	SP,	#60H
		MOV	IF,	#9FH
		MOV	IP,	#03H
		SJMP	$
INT0:		.							;INT0 interrupt service program
			.
			.
		RETI
IT0:		PUSH	DPL						; IT0 interrupt service program
		PUSH	DPH
		MOV	DPTR,	#True_IT0
		PUSH	DPL
		PUSH	DPH
		ANL		IP,	#100000011B
		RETI							;pseudo-RETI
True_IT0:		.						
			.
			.
		POP	DPH
		POP	DPL
		ORL	IP,	#00011100B
		RETI
INT1:		.							; INT1 interrupt service program
			.
			.
		RETI
IT1:		PUSH	DPL						;IT1 interrupt service program
		PUSH	DPH
		MOV	DPTR,	#True_IT1
		PUSH	DPL
		PUSH	DPH
		CLR		PS						;”pseudo-RETI”
		RETI
True_IT1:		.
			.
			.
		POP	DPH
		POP	DPL
		SETB	PS
		RETI
INTP:	PUSH	DPL						;Serial port interrupt service program
		PUSH	DPH
		MOV	DPTR,	#SPINT
		PUSH	DPL
		PUSH	DPH
		RETI
SPINT:			.
			.
			.
		POP	DPH
		POP	DSL
		RETI