[SOLVED] How to do if-else in assembly language?

skyassasin16 · Jan 13, 2011

hi everyone, im new here..
im using MPLAB IDE and working on PIC16F877A.
how can i translate this algoritm into an assembly language?

if W = 1
goto sub_1
if W = 2
goto sub_2
if W = 3
goto sub_3

thanks

wp100 · Jan 13, 2011

Hi,

You can use the Assembler Directives - see the full list in the Microchip Assembler Users Guilde.

Code:

DISPLAY = 204  ;Display 162 = 16X2 character, 204 = 20x4



       IF DISPLAY == 204
       
       ; user code
       
        ENDIF

       IF DISPLAY == 162
        
       ; user code
        
       ENDIF

krishna1234 · Jan 13, 2011

DECFSZ W, 1
goto L1
goto sub_1
L1

ECFSZ W, 1
goto L2
goto sub_2
L2

ECFSZ W, 1
goto L3
goto sub_3
L3 : ;non 123

---------- Post added at 15:22 ---------- Previous post was at 15:09 ----------

this only for positive values, if there -ve values exists first check the borrow then use this code.

keith1200rs · Jan 13, 2011

BE CAREFUL. Assembler directives are totally different to conditional assembly code. As assembler directive such as IF ENDIF will include the code in your final assembly code or not based on a value when you assemble it - NOT AT RUNTIME.

Keith.

bobsanjose · Jan 13, 2011

skyassasin16,
Your style looks a lot like Basic. My recommendation would be to write this small code in "C" and hand it over to the MPLAP C-Compiler. Then look into the list-file how the C-Compiler does it. Might be a bit cryptic in the beginning but if you read through it a few times you should get the hang of it.

hth, Bob

PaulHolland · Jan 13, 2011

The following example is a working example of how a switch statement can be made, NOTE only works if your index value is like in your example 0,1,2,3,4,5,6,7 etc..

Code:

SWITCH:		        movwf	tmp 			; Save the input value
				movlw	HIGH (table + 1)  ; Calculate the start of the table
				movwf	PCLATH		;
				movf	        tmp,w	        ;
				addlw 	LOW  (table + 1)  ; Add input value to Table Pointer				
				btfsc	        STATUS,C	        ;
				incf	        PCLATH,f	        ; Adjust table start if it crosses a boundary of 256.

table:			        movwf	 PCL
	                        goto           L0
				goto           L1
				goto           L2		   
				goto           L3

L0:                                                   ; Put your code here for W = 0
                                return
L1:                                                   ; Put your code here for W = 1
                                return
L2:                                                   ; Put your code here for W = 2
                                return
L3                                                    ; Put your code here for W = 3
                                return

skyassasin16 · Jan 16, 2011

I'm new to this forum, how can I thank you guys? are there are any reputation scoring in here?

btbass · Jan 16, 2011

Some time ago I wrote a utility to help write assembler code for Pic16 series micros and posted it on eda board here.

It can generate code for delays of various lengths, loops conditionals, etc.

No install is needed, just extract all the files to a directory. Call the directory PicHelp or whatever you like.
Generates code for common constructs in programming.

Please give it a go and see if it helps.

keith1200rs · Jan 16, 2011

skyassasin16 said:
I'm new to this forum, how can I thank you guys? are there are any reputation scoring in here?

You should see a "Helpful? Please click" button at the bottom of most messages if you are logged in. Click that for the helpful posts.

Keith

skyassasin16 · Jan 20, 2011

PaulHolland said:

The following example is a working example of how a switch statement can be made, NOTE only works if your index value is like in your example 0,1,2,3,4,5,6,7 etc..

Code:

SWITCH:		        movwf	tmp 			; Save the input value
				movlw	HIGH (table + 1)  ; Calculate the start of the table
				movwf	PCLATH		;
				movf	        tmp,w	        ;
				addlw 	LOW  (table + 1)  ; Add input value to Table Pointer				
				btfsc	        STATUS,C	        ;
				incf	        PCLATH,f	        ; Adjust table start if it crosses a boundary of 256.

table:			        movwf	 PCL
	                        goto           L0
				goto           L1
				goto           L2		   
				goto           L3

L0:                                                   ; Put your code here for W = 0
                                return
L1:                                                   ; Put your code here for W = 1
                                return
L2:                                                   ; Put your code here for W = 2
                                return
L3                                                    ; Put your code here for W = 3
                                return

When I try this sir, when W value goes higher than 3, the whole program crashes. I try to add more goto in the table subroutine but still crashes. anyways, thanks everyone.

PaulHolland · Jan 20, 2011

Do not forget to put a return behind every part of code !. I use this upto 256 and they all work. Also call this part of code with a call SWITCH !!

Code:

SWITCH:		        movwf	tmp 			; Save the input value
				movlw	HIGH (table + 1)  ; Calculate the start of the table
				movwf	PCLATH		;
				movf	        tmp,w	        ;
				addlw 	LOW  (table + 1)  ; Add input value to Table Pointer				
				btfsc	        STATUS,C	        ;
				incf	        PCLATH,f	        ; Adjust table start if it crosses a boundary of 256.

table:			        movwf	 PCL
	                        goto           L0
				goto           L1
				goto           L2		   
				goto           L3
	                        goto           L4
				goto           L5
				goto           L6		   
				goto           L7


L0:                                                   ; Put your code here for W = 0
                                nop etc..
                                nop etc..
                                return
L1:                                                   ; Put your code here for W = 1
                                return
L2:                                                   ; Put your code here for W = 2
                                return
L3                                                    ; Put your code here for W = 3
                                return
L4:                                                   ; Put your code here for W = 4
                                return
L5:                                                   ; Put your code here for W = 5
                                return
L6:                                                   ; Put your code here for W = 6
                                return
L7                                                    ; Put your code here for W = 7
                                return

btbass · Jan 20, 2011

Did you try my PicHelp application?
It will generate an 'if else' for you with the click of a button!

skyassasin16 · Jan 21, 2011

Yes, I tried the PicHelp also but unfortunately, even if the value is correct e.g., value == 1, is does not jump into the _TRUE subroutine. dunno what im doing wrong,. =(

btbass · Jan 21, 2011

I don't understand?
If I ask it if x == 1, it generates this code: which is correct.

Code:

;------ if routine

_IF	movf	x,w
	sublw	.1
	bnz	_FALSE

_TRUE	;CODE BODY HERE!

_FALSE	;FAILED IF TEST

vishy71 · Jan 21, 2011

Hi

movf (your register name),0
sublw 0x01

btfsc 0x03,2 ;if Z bit in STATUS register is 1 then goto line1
goto (or call) line1
goto (or call) line2 ;Z bit is 0 (your register value <=> 0x01 (1)) so got line2

line1
;your rutin

line2
;your rutin

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[SOLVED] How to do if-else in assembly language?

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