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'[PIC] 1s delay with 20MHz 16F84A'
2009\01\20@155129 by 4e fte

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I have seen some examples of 1s delay with a 32KHz or 4MHz frequencies
but am still confused about how to produce this with 20MHz. Could
someone please assist me on this? Thanks.

2009\01\20@161316 by Scott Larson

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On Tue, Jan 20, 2009 at 2:51 PM, 4e fte <spam_OUT4eftefjTakeThisOuTspamgmail.com> wrote:
> I have seen some examples of 1s delay with a 32KHz or 4MHz frequencies
> but am still confused about how to produce this with 20MHz. Could
> someone please assist me on this? Thanks.


I don't think anyone would advise running the 84A at 20MHz, but all
you have to do is adjust your counters. There's an automatic code
generator on the piclist site that will generate this for you.

-Scott

2009\01\20@162151 by solarwind

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On Tue, Jan 20, 2009 at 3:51 PM, 4e fte <.....4eftefjKILLspamspam@spam@gmail.com> wrote:
> I have seen some examples of 1s delay with a 32KHz or 4MHz frequencies
> but am still confused about how to produce this with 20MHz. Could
> someone please assist me on this? Thanks.

You can try using this tool:
http://www.piclist.com/techref/piclist/codegen/delay.htm if you're
using assembler.

Here, I generated it:

http://pastebin.com/f5b0700e4

Just a question, why are you using such an old chip? There a lot newer
chips which sport more advanced features for lower prices, such as the
16F886.


--
solarwind

2009\01\20@162228 by solarwind

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On Tue, Jan 20, 2009 at 4:13 PM, Scott Larson <goldscottspamKILLspamgmail.com> wrote:
> I don't think anyone would advise running the 84A at 20MHz
> -Scott

And why not?

--
solarwind

2009\01\20@163214 by cdb

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face
There is some code on my website and also on the Piclist for
generating timing periods - look for Bresenham algorithm - my code is
taken from the Piclist one.

Colin
--
cdb, .....colinKILLspamspam.....btech-online.co.uk on 21/01/2009

Web presence: http://www.btech-online.co.uk  

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2009\01\20@163309 by Michael Rigby-Jones

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> -----Original Message-----
> From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu] On
Behalf
> Of Scott Larson
> Sent: 20 January 2009 21:13
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] 1s delay with 20MHz 16F84A
>
> On Tue, Jan 20, 2009 at 2:51 PM, 4e fte <@spam@4eftefjKILLspamspamgmail.com> wrote:
> > I have seen some examples of 1s delay with a 32KHz or 4MHz
frequencies
{Quote hidden}

The 16F84A was (is?) available in a 20MHz grade.  However, running a PIC
unnecessarily fast can cause issues such as Read-Modify-Write problems
that you may not see at lower speeds, and increases power consumption.

Regards

Mike

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2009\01\20@163632 by olin piclist

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4e fte wrote:
> I have seen some examples of 1s delay with a 32KHz or 4MHz frequencies
> but am still confused about how to produce this with 20MHz. Could
> someone please assist me on this?

It's the same thing, just count higher.

********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\01\20@170223 by Jinx

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You modify what I posted the other day

20MHz/4 = 5MHz (200ns instruction cycle)

=> 5,000,000 / 256 = 19,531.25 IRQs / sec. Leave as is if you
don't mind losing (0.25 * 256 * 200ns) = 12.8us per second. IOW
the 'second' will actually be 999.9872ms

If you use a 19.6608MHz crystal and set TMR0 pre-scaler to 256

(19,660,800/4) / 65536 = exactly 75 IRQs / second

I've got something like that running right in front of me, generating
150 IRQ/sec for a project. Reload the timer with $8000 (bsf bit15),
divide by 3, => 50Hz

2009\01\20@171655 by Richard Seriani, Sr.

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----- Original Message -----
From: "4e fte" <KILLspam4eftefjKILLspamspamgmail.com>
To: "Microcontroller discussion list - Public." <RemoveMEpiclistTakeThisOuTspammit.edu>
Sent: Tuesday, January 20, 2009 3:51 PM
Subject: [PIC] 1s delay with 20MHz 16F84A


>I have seen some examples of 1s delay with a 32KHz or 4MHz frequencies
> but am still confused about how to produce this with 20MHz. Could
> someone please assist me on this? Thanks.
> --

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