5.2. Structure of a program in assembler

The following program shows the basic structure of a program in assembler.

 ;************************************************* *********
; Example structure of a program in assembler
, The microcontroller 8051.
;
; Program to blink all the bits of Port 0
, With a certain time.
;
; Author: Rafael Aranda
; Date: 20-10-2009
: Version: 1.0
;************************************************* *********

$ NOMOD51
$ INCLUDE (REG51.INC)

		STRUCTURE NAME
 
STACK EQU 030H; address stack pointer

;*************************************
; Start interrupt vectors
;*************************************

		USING 0

		ORG 0H; Source Code (Location of the ROM)

VECTOR: JMP START; Reset

		VECTOR ORG +3 H; INT0
         
		VECTOR ORG +0 BH; Timer 0
          
		VECTOR ORG +13 H; INT1

		VECTOR ORG +1 BH; Timer 1

		VECTOR ORG +23 H; Puerto series RI + TI

		VECTOR ORG +2 BH, Timer 2
        
;********************************
; Tasks initial preparation
;********************************         

 		ORG VECTOR H +30

START: MOV SP, # STACK-1; Set stack pointer
         	MOV PSW, # 00000000B; Selects register bank 0
		MOV P1, # 0H; Prepare port	


;*******************
Major Programme
;*******************

PROGRAM: MOV P1, # 0H; Put the bits of Port 0 to 0
		CALL DELAY; Perform a delay
		MOV P1, # 0FFH; Put the bits of Port 0 to 1
		CALL DELAY; Perform a delay
		JMP PROGRAM; Restating infinitely

;***************************
; Subroutine timing
;***************************

DELAY: MOV R2, # 7FH
RET_3: MOV R1, # 0FFH
RET_2: MOV R0, # 0FFH
RET_1: DJNZ R0, RET_1	
		DJNZ R1, RET_2
		DJNZ R2, RET_3
		RET

	END