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'[pic:] Question about pic datasheet'
2004\06\05@022239 by Shawn Wilton

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Ok, I'm looking at this design note:
http://ww1.microchip.com/downloads/en/AppNotes/00232a.pdf  and on page 6
they mention a CCP1RIL bit.  But I'm looking at the datasheet for the
16f627 that they are basing the design off of and I can't find the bit
anywhere...

Perhaps someone can help me decipher what is apparently another typo?

Design note:
http://ww1.microchip.com/downloads/en/AppNotes/00232a.pdf

Datasheet:
http://ww1.microchip.com/downloads/en/DeviceDoc/40300c.pdf


-Shawn

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2004\06\05@023109 by Charles Craft

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Pg. 61 of the datasheet - CCP module.
What's not to see?

-----Original Message-----
From: Shawn Wilton <spam_OUTshawnTakeThisOuTspamBLACK9.NET>
Sent: Jun 5, 2004 2:22 AM
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: [pic:] Question about pic datasheet

Ok, I'm looking at this design note:
http://ww1.microchip.com/downloads/en/AppNotes/00232a.pdf  and on page 6
they mention a CCP1RIL bit.  But I'm looking at the datasheet for the
16f627 that they are basing the design off of and I can't find the bit
anywhere...

Perhaps someone can help me decipher what is apparently another typo?

Design note:
http://ww1.microchip.com/downloads/en/AppNotes/00232a.pdf

Datasheet:
http://ww1.microchip.com/downloads/en/DeviceDoc/40300c.pdf


-Shawn

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2004\06\05@023524 by Shawn Wilton

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The bit in question.  I'm looking for the CCP1RIL bit as mentioned in
the design note, but there NO reference of it in the datasheet.  I'm
trying to figure out what bit or byte for that matter, they really meant.

-Shawn

Charles Craft wrote:

>Pg. 61 of the datasheet - CCP module.
>What's not to see?
>
>{Original Message removed}

2004\06\05@024526 by Jason Harper

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Shawn wrote:
> they mention a CCP1RIL bit.  But I'm looking at the datasheet for the
> 16f627 that they are basing the design off of and I can't find the bit
> anywhere...

I think they meant the CCPR1L byte - changing that between zero and the
calculated 50% duty cycle value would give you glitchless on/off modulation
of the output.
       Jason Harper

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2004\06\05@025605 by Shawn Wilton

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Ok, that's what I was wondering.  I was bouncing between that and the
t2con register for turning off the timer all together.

Now I just need someone to help me understand how you modulate that
output.  Do you modulate by just turning the damn thing on and off at
some other timer interval so you can produce a 1 that's shooting out a
pwm frequency greater than your modulation rate?  If that's the case,
then how would you go about doing that?  Would this require a second
timer that runs at some "baud rate" that pulls data from a register and
sends it out the pwm?


-Shawn


Jason Harper wrote:

{Quote hidden}

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2004\06\05@025812 by Jinx

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> The bit in question.  I'm looking for the CCP1RIL bit as mentioned in
> the design note, but there NO reference of it in the datasheet.  I'm
> trying to figure out what bit or byte for that matter, they really meant.

"To modulate the data, one can turn the drive signal on and off by
setting and clearing the CCP1RIL bit"

Perhaps TMR2ON ?

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2004\06\05@031513 by Jan-Erik Soderholm

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Shawn Wilton wrote :

> Now I just need someone to help me understand how you modulate that
> output.

I'm looking at the AP note. So you need to output some
specific number of cycles of the carrier signal (as
produced by the PWM module), right ? Probably a varying
number of cycles depending on the data.

> Do you modulate by just turning the damn thing on and off at
> some other timer interval so you can produce a 1 that's shooting out a
> pwm frequency greater than your modulation rate?

First you must have a method to put the PWM output
on/off. The AP note uses the TRIS bit of RB4 for this.
Probably OK.

> If that's the case,  then how would you go about doing that?
> Would this require a second timer that runs at some "baud rate"
> that pulls data from a  register and sends it out the pwm?

You don't have to tie up a hole counter for this, just
another software counter.

Note that each "bit" wil be a specific number of periods of the
PWM signal. So you can just as well count the number of PWM
periods output and, when the correct number is reached, just
shut of the PWM output.

This can be done easily by using the "overflow interrupt" of the
timer controling the PWM module. In the ISR you then just
decrement a counter and, when it reach zero, shut the PWM output
off.

Using this method it's also easy to get clean on/off so you
always gets whole and clean PWM pulses. You could either also
control the "on" of the PWM in the ISR, or just monitor the
"timer interrupt flag" somewhare else in your code.

I used this concept in an IR sender using the PWM module to
produce the 38Khz carrier, and using sequences of PWM
pulses of different length to idicate "start", "1" and "0" bits.
Looks very much the same as this application...

Jan-Erik.

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2004\06\05@160919 by Shawn Wilton

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> First you must have a method to put the PWM output
> on/off. The AP note uses the TRIS bit of RB4 for this.
> Probably OK.

You think the tristate should be flipped eh?  Why not just use the duty
cycle as a switch? You have a preference I take it?

>
>
>>If that's the case,  then how would you go about doing that?
>>Would this require a second timer that runs at some "baud rate"
>>that pulls data from a  register and sends it out the pwm?
>
>
> You don't have to tie up a hole counter for this, just
> another software counter.

A counter is a counter though.

{Quote hidden}

I like that idea.  I'll look in to it some more.

Thanks.

-Shawn


{Quote hidden}

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2004\06\05@164042 by Jan-Erik Soderholm

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Shawn Wilton wrote :

> > First you must have a method to put the PWM output
> > on/off. The AP note uses the TRIS bit of RB4 for this.
> > Probably OK.
>
> You think the tristate should be flipped eh?  Why not just
> use the duty cycle as a switch? You have a preference I take it?

No particular preference, I'd just use what's easiest.
If you'd use the duty cycle, you have to "remember" what it was set
to until it's time to start the PWM again. The TRIS bit are just a
single bcf/bsf instruction. Faster and less code.

{Quote hidden}

Sorry, I should have written "tie up a hole timer"...
I read "a second timer" in your text as a "hardware timer",
which isn't needed, as I wrote.

Best Regards,
Jan-Erik.

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2004\06\05@165224 by Shawn Wilton

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I'll keep that in mind.  Thx.

Jan-Erik Soderholm wrote:

{Quote hidden}

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