Creating an Assembler File Using a Text Editor

One of the greatest features of assembly language is that it is text based and can be wrritten in virtually any test editor.

• To create the assembler file I suggest you use the text editor, "Notepad".
• Complete the following steps;
  • copy and paste the following text (on this page) into the text editor,
  • save the text into a directory called "blink",
  • the filename of the saved file should be "blink.asm"

The .asm delineates the code as an assembler file.

;blink.asm
;This is a program which turns on and off pin B0
;Port A is set as an input and port B as an output
;The prescaler is set in the option register to 256 (to give timing pulse of 1/32 s)
;1s and 0.5 s time delays are created in the subroutines
;uses a 32768 Hz xtal

;*************************************************************

;EQUATES SECTION
   TMR0 	EQU 1 		;TMR0 means 1
   STATUS 	EQU 3 		;STATUS means 3
   PORTA 	EQU 5 		;PORTA means 5
   PORTB 	EQU 6 		;PORTB means 6
   ZEROBIT EQU 2 		;ZEROBIT means 2
   COUNT 	EQU 20H 	;COUNT means 20h
   OPT_REG EQU 81H 	;OPT_REG means 81h

;*************************************************************

 	PROCESSOR 16F628a 	;means we are using the 16F628a chip
   __CONFIG H'2168' 	;sets config bits
   ORG 0 				;the start address in program memory is 0
   GOTO START 			;go to START!

;*************************************************************

;SUBROUTINE SECTION

;1.0 SECOND DELAY
   DELAY1 	CLRF 	TMR0 			;sets the TMR0 register to 0
   LOOPA 	MOVF 	TMR0,W 			;moves the contents of TMR0 reg to W reg
   		SUBLW 	.32 			;the W reg is sub from 32 and result put in W reg
   		BTFSS 	STATUS,ZEROBIT 	;if ZEROBIT is 1(arith op is zero) then next op is skipped
   		GOTO 	LOOPA 			;GOTO LOOPA
   		RETLW 	0 				;return to main program with 0 in W reg

;0.5 SECOND DELAY
   DELAYP5 CLRF 	TMR0 			;sets the TMR0 register to 0
   LOOPB 	MOVF 	TMR0,W 			;moves the contents of TMR0 reg to W reg
   		SUBLW 	.16 			;the W reg is sub from 16 and result put in W reg
   		BTFSS 	STATUS,ZEROBIT 	;if ZEROBIT is 1(arith op is zero) then next op is skipped
   		GOTO 	LOOPB 			;GOTO LOOPB
   		RETLW 0 				;return to main program with 0 in W reg

;************************************************************

;CONFIGURATION SECTION

START 	BSF 	STATUS,5 	;activates addressing (of ram) to bank 1

 		MOVLW 	B'00011111' ;puts 00011111 into W reg
   	MOVWF 	PORTA 		;puts W reg into PORTA direction reg (input)

 		MOVLW 	B'00000000' ;puts 00000000 into W reg
   	MOVWF 	PORTB 		;puts W reg into PORTB direction reg (input)

 		MOVLW 	B'00000111' ;puts 00000111 into W reg
   	MOVWF 	OPT_REG 	;puts W reg into option reg to set prescaler

 		BCF 	STATUS,5 	;activates addressing (of ram) to bank 2
   	CLRF 	PORTA 		;sets PORTA data (input) status to 0's
   	CLRF 	PORTB 		;sets PORTB data (output) status to 0's

;*********************************************************

;PROGRAM STARTS NOW

BEGIN 	BSF 	PORTB,0 	;turns on B0
   	CALL 	DELAY1 		;delays 1.0 seconds
   	BCF 	PORTB,0 	;turns off B0
   	CALL 	DELAYP5 	;delays 0.5 seconds
   	GOTO 	BEGIN 		;loops to begin

 		END 				;must have an end statement