16 bit count down - PIC16

Hi

Can someone please help me with the asm code for a 16-bit count down loop
for a PIC16 processor.

The following code does not count down properly. It exits the loop when both
0Ch and 0Dh are 1.

            movlw h'FF'
            movwf 0Ch
           movwf 0Dh
loop    decfsz 0Ch
           goto loop
           decfsz 0Dh
           goto loop
           return


Thanks

Mauritz

Which PIC16 is it?

Mauritz Geyser wrote:
> Hi
> 
> Can someone please help me with the asm code for a 16-bit count down loop
> for a PIC16 processor.
> 
> The following code does not count down properly. It exits the loop when both
> 0Ch and 0Dh are 1.
> 
>             movlw h'FF'
>             movwf 0Ch
>            movwf 0Dh
> loop    decfsz 0Ch
>            goto loop
>            decfsz 0Dh
>            goto loop
>            return
> 
> 
> Thanks
> 
> Mauritz
> 
> 

      movlw h'FF'
      movwf 0Ch
      movwf 0Dh
loop:  // Value probed here
      movf 0Ch, f
      btfsc STATUS, Z
      goto turnaround
      decf 0Ch, f
      goto loop

turnaround:
      movf 0Dh, f
      btfsc STATUS, Z
      goto exit
      movwf 0Ch
      decf 0Dh
      goto loop      


If you place code at the "Value probed here" marker, you'll see the values

FFFF ... FF01 ... FF00 FEFF ... 0001 0000 exit


But do you really need it ? If it's to iterate a fixed number of time without using the counter value, you just need to adjust the constant.
Using incfsz might be more efficient. Just place in 0C and 0D (0x10000 - number of iter).

      clrf 0Ch
      clrf 0Dh
loop:  // Value probed here
      incfsz OCh
      goto loop
      incfsz 0Dh
      goto loop


Sylvain