On Thu, 27 Aug 2015, Josh Koffman wrote:

> Hi all,
>
> Amongst all the other things on my plate right now, I'd like to make a
> small library to do Bit Angle Modulation on some of my projects. I
> made one years ago in assembly, but now I'd like to do it in XC8.
>
> For reference, there are some great posts on BAM on the PicBasic forums h=
ere:
>
> http://www.picbasic.co.uk/forum/showthread.php?p=3D45597
> http://www.picbasic.co.uk/forum/showthread.php?t=3D10564
>
> Because the PIC will be doing many things, I am considering using a
> high priority interrupt for the BAM, but keeping my high priority ISR
> as small as possible (which is probably a good idea regardless). To
> accomplish this, I want to create the 8 "slices" that I will output in
> my main line, so that all the BAM ISR has to do is take that variable
> and put it on the port.
>
> My question is, what would be the best way to handle this in C? When I
> did it in assembly I used a rotate (rotate right if I remember
> correctly), then read the carry bit. But then I was also doing it at
> the moment of outputting, so there was no intermediate stored
> variable.
>
> My current thought is to define a typedef that lets me access the
> individual bits, then a bunch of if/else statements that check the bit
> of the source value, and if it's a 1 set the bit of the corresponding
> "slice" variable. This would result in a lot of if statements though,
> so I'm wondering if there's a slicker way to do this.
>
> I'm trying to avoid dropping into ASM to do this for a few reasons.
>
> Any thoughts?
>
> Thanks!
>
> Josh

>From what I've read from the description of BAM, if I were doing this in C=
=20
I would do it like this:

// globals
unsigned char	bit_cnt, bit_mask, value_out;

void set_BAM(unsigned char val)
{
 	// disable interrupts - how do you do this in XC8?

 	bit_cnt   =3D 1;
 	bit_mask  =3D 0x80;
 	value_out =3D val;

 	// enable interrupts
}

void service_BAM()
{
 	bit_cnt--;

 	if (bit_cnt =3D=3D 0)
 	{
 		if ((bit_mask & 0x80) =3D=3D 0)
 		{
 			bit_mask <<=3D 1;
 		}
 		else
 		{	bit_mask =3D 1;
 		}

 		bit_cnt =3D bit_mask;

 		// I'm assuming the output pin is defined at compile time

 		if ((value_out & bit_mask) =3D=3D 0)
 		{
 			// reset output pin
 		}
 		else
 		{	// set output pin
 		}
 	}
}

Regards
Sergio Masci
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.