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DECFSZ command problem

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MessUpMymind

New Member
hi there,

Hey , i got stuck in some problem that i dont understand what is going on actually..

i got the following code:
Code:
Start:	movlw 	b'11111000'
		movwf	col1

		MOVLW	b'00100000'
		MOVWF	col2
	
		MOVLW	b'00100000'
		MOVWF	col3
	
		movlw	b'00100000'
		movwf	col4
	
		movlw	b'11111000'
		movwf	col5	
		GOTO	Run1

Run4:	bsf		PORTB,1
		call	CLK
		call	DELAY
		bcf		PORTB,1
		goto	$+2
	
Run3:	bsf		PORTB,1
		call	CLK
		call	DELAY
		bcf		PORTB,1
		goto	$+2
	
Run2:	
		bsf		PORTB,1
		call	CLK
		call	DELAY
		bcf		PORTB,1
		goto	$+8	

Run1:	bsf		PORTB,1
		movlw	d'2'
		movwf	shift1
		movlw	d'2'
		movwf	shift2
		movlw	d'2'
		movwf	shift3
		movf	col1,w
		movwf	PORTD
		CALL	CLK	     ; call clock to move the data to collumns
		call	DELAY
		bcf		PORTB,1
		
	
		movf	col2,w
		movwf	PORTD
		CALL	CLK
		call	DELAY

		movf	col3,w
		movwf	PORTD
		call	CLK
		call	DELAY

		movf	col4,w
		movwf	PORTD
		call	CLK
		call	DELAY

		movf	col5,w
		movwf	PORTD
		call	CLK
		call	DELAY

		bcf		PORTB,2
		bsf		PORTB,2

		clrf	PORTD

		call	DELAYLONG
			
		[COLOR="Red"]decfsz	shift1,f
		GOTO	Run2 ;can
		decfsz	shift2,f
		GOTO	Run3
		decfsz	shift3,f
		GOTO	Run4
		GOTO	Run1[/COLOR]
what i got is , the first time it loop .. it work perfectly fine, but when come to second time it only keep looping on the first decfsz loop and it wont go to second decfsz in short it will only display Run2 forever and wont goes to Run3 and Run4.

Help is much appreciated =)
 

Pommie

Well-Known Member
Most Helpful Member
That is because the second time shift1 will contain zero and so it will loop 256 times. The goto $+8 jumps over the variable setup. I personally hate to see goto $+x in any code, it is much better to use a label.

Maybe you should explain what you are trying to do.

Mike.
 

kchriste

New Member
Forum Supporter
it will only display Run2 forever and wont goes to Run3 and Run4.
Are you sure it is forever and not just a very long time? After the decfsz shift1 instruction has run it's course, shift1 is equal to zero, so that the next time you run the decfsz shift1 instruction, shift1 will be equal to 255. This make the loop much longer than the first pass.

The reason for difference in the first run vs the subsequent runs is this section of code:


Run2:
bsf PORTB,1
call CLK
call DELAY
bcf PORTB,1
goto $+8

Run1: bsf PORTB,1
movlw d'2' ;This code missed on subsequent runs
movwf shift1 ;because of goto $+8 above so shift1 = 0
movlw d'2'
movwf shift2
movlw d'2'
movwf shift3
movf col1,w
movwf PORTD
CALL CLK ; call clock to move the data to collumns
call DELAY
bcf PORTB,1
 

MessUpMymind

New Member
hi pommie ,

when all Run1-4 is done then second loop i did fill back the counter with number and it no longer 0.. therefore , it should come out the same output as the first time it loop. I am trying to shift a character by sending in off for the first row, second row and so on so on.

Thanks =)
 

MessUpMymind

New Member
Are you sure it is forever and not just a very long time? After the decfsz shift1 instruction has run it's course, shift1 is equal to zero, so that the next time you run the decfsz shift1 instruction, shift1 will be equal to 255. This make the loop much longer than the first pass.

The reason for difference in the first run vs the subsequent runs is this section of code:


Run2:
bsf PORTB,1
call CLK
call DELAY
bcf PORTB,1
goto $+8

Run1: bsf PORTB,1
movlw d'2' ;This code missed on subsequent runs
movwf shift1 ;because of goto $+8 above so shift1 = 0
movlw d'2'
movwf shift2
movlw d'2'
movwf shift3
movf col1,w
movwf PORTD
CALL CLK ; call clock to move the data to collumns
call DELAY
bcf PORTB,1
hi kc ,

hmm you got some misunderstanding in that code , sorry for the mess =(.
for the $+8 is only true
after the first loop Run1
and this following is my structure how the program works
First loop:Run1
Second loop:Run1+Run2 together
Third loop: Run1+Run2+Run3 together
Fourth loop: Run1+Run2+Run3+Run4

all this run by sending in more 0, after the fourth loop done , i will go back to Run1 and fill back the counter value so it no longer 0 inside those shift register doesnt it?? and it will go back to the same looping structure again.

Thanks
 
Last edited:

kchriste

New Member
Forum Supporter
Both Pommie and I have told you what the problem is. Look at your code again or run it in MPLAB SIM to see how it loops and what happens to the shift1 variable.
 
Last edited:

MessUpMymind

New Member
hi kc ,

thanks for your help , i will look into the MPlab sim...i understand what you all mean now , so if the shift1=0 then it will loop 256times only goes to shift 2 right?? therefore actually is there anyway i can program to make it such a way that after the shift1=0 i can goes to shift2 immediately to check the condition??
 

kchriste

New Member
Forum Supporter
this following is my structure how the program works
First loop:Run1
Second loop:Run1+Run2 together
Third loop: Run1+Run2+Run3 together
Fourth loop: Run1+Run2+Run3+Run4
It's a little crude, but a simple way to do this would be to turn Run1 through Run4 into subroutines:
Code:
Run4: 
        bsf     PORTB,1
        call    CLK
        call    DELAY
        bcf     PORTB,1
        return
And then simply do this:
Code:
call Run1

call Run1
call Run2

call Run1
call Run2
call Run3

call Run1
call Run2
call Run3
call Run4
 
Last edited:

Wond3rboy

Member
Another thing a noticed from the code is that(may be i am wrong) but arent you supposed to output on the LATx register rather then the PORTx register itself? I know it shouldnt be causing a problem but it did when i tried it.
 

kchriste

New Member
Forum Supporter
Yes, that is correct. Don't know which PIC MessUpMymind is using so it may, or may not, have a LATx register for the port.
 

MessUpMymind

New Member
hi kc, mike and wonderboy

Thanks a lot!!you guys just great..i solved the problem now and i am using 16F877A, so is there use LATx Register will be better??? or if i follow to send direct to PORT will be fine too?? thanks for sparing time with me =)

Best regards,
TK
 

Wond3rboy

Member
Hi TK,

From the data sheet i dont see any latch registers for the 16F877a and also in the example(in the datasheet) they are clearing it directly so guess it will work for this chip.


PS: Shows that you should tell the Chip being used or you can end up getting wrong solutions to your problems(like i did this time).
 

blueroomelectronics

Well-Known Member
The LATx commands are only available on 16bit or higher cores ie: 18F, 24F, 30F, 33F. There are a couple of new 16F series PICs that may have it too.
 
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