Ooooh, me likey.  Perfect code for the job.  Thank you so much.  After
changing the rrf to rrcf, it works great.  Thanks again.

On 5/26/05, Mark Rages <markrages@gmail.com> wrote:
> On 5/26/05, Dave Turner <dave.w.turner@gmail.com> wrote:
> > Hi again guys,
> >
> > I am currently working on a software PWM.  I got it to work fine with
> > 1 pin, and now I'm extending it to 8 pins.  I am using a regularly
> > incremented PWMtimer, and 8 GPRs, called PWMlevel 1 to 8.  Inside the
> > PWMupdate function, I use a loop, and indirect addressing to access
> > each pwmlevel, and check if it's higher or lower than pwmtimer, to
> > decide when to turn it off.  Therefore, the pwmlevel decides on
> > average, how high the pin is.
> >
> > All the loop code works just fine, in checking each pwmlevel, but then
> > I come to set or clear each bit on portb.  I need a way to set or
> > clear a particular bit, depending on a variable, i.e. if the variable
> > is 4, I want to set/clear bit 4.  I cannot think of a way to access a
> > bit, specified on the fly.  The only method I could think of is to use
> > the variable as a loop counter, and in each loop, bit shift d'1' to
> > the left, and then move this to portb.  Unfortunately, this would
> > disturb all the other bits in porta.
> >
> > Thanks in advance.
> 
> Something like this?  (untested code!)
> 
> ; Be careful where this goes in the program space -- the addwf must
> clear the carry bit...
> ; Uses one scratch file, named scratch
> set_bit macro           ; bit is in 'w' 0..7
>         clrf scratch
>         bsf scratch,0
>         addwf PCL,f
>         rrf scratch,f           ; 0100 0000
>         rrf scratch,f           ; 0010 0000
>         rrf scratch,f           ; 0001 0000
>         rrf scratch,f           ; 0000 1000
>         rrf scratch,f           ; 0000 0100
>         rrf scratch,f           ; 0000 0010
>         rrf scratch,f           ; 0000 0001
> 
>         movfw scratch
>         iorwf PORTA,f
> endm
> 
> set_bit macro           ; bit is in 'w' 0..7
>         clrf scratch
>         bsf scratch,0
>         addwf PCL,f
>         rrf scratch,f           ; 0100 0000
>         rrf scratch,f           ; 0010 0000
>         rrf scratch,f           ; 0001 0000
>         rrf scratch,f           ; 0000 1000
>         rrf scratch,f           ; 0000 0100
>         rrf scratch,f           ; 0000 0010
>         rrf scratch,f           ; 0000 0001
>         comf scratch,w
>         andwf PORTA,f
> endm
> 
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-- 

Dave
All us base are belong to you.

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