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'[PIC:] pin function defaults...'
2004\01\22@035418 by William Chops Westfield

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speaking of the f84 being easier to use cause it's simpler:

Is there a table somewhere that lists, for each PIC, the
default (power-up) usage of each pin?  This doesn't seem
to be very obvious from the data sheets (or I'm missing
something - it took me an embarassingly long time to figure
out which peripheral was interfering with using some of
the GPIO pins on a 16F675 as outputs (the data sheet is
pretty clear when you have to turn off a peripheral or
change tris to switch between digital and analog inputs,
but it's not so clear which special functions interfere
with digital output...)

Thanks
Bill W

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2004\01\22@071447 by Olin Lathrop

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William Chops Westfield wrote:
> Is there a table somewhere that lists, for each PIC, the
> default (power-up) usage of each pin?

Not that I know of.

> This doesn't seem
> to be very obvious from the data sheets

Actually, it's pretty simple.  When there is a choice, all peripherals off,
all pins are inputs.  The inputs are analog when they can be, digital
otherwise.  Some pins are dedicated or controlled by the configuration
fuses, so the above doesn't apply to them.


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2004\01\22@075255 by John J. McDonough

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----- Original Message -----
From: "Olin Lathrop"
Subject: Re: [PIC:] pin function defaults...


> Actually, it's pretty simple.  When there is a choice, all peripherals
off,
> all pins are inputs.

Not always true, look at the 628.  Perhaps it's always true that when there
is a comparator it powers up as a comparator.

It does seem as though it takes more than it should to dig this out of the
datasheets.  On the other hand, I think most folks work with a relatively
small number of parts, so it's not a huge effort to learn the quirks of the
relevant models.

72/73 de WB8RCR    http://www.qsl.net/wb8rcr
didileydadidah     QRP-L #1446 Code Warriors #35

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2004\01\22@085733 by Olin Lathrop

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John J. McDonough wrote:
>> Actually, it's pretty simple.  When there is a choice, all
>> peripherals off, all pins are inputs.
>
> Not always true, look at the 628.  Perhaps it's always true that when
> there is a comparator it powers up as a comparator.

It would have been true if you hadn't snipped the very next sentence where I
said that any pins that can be analog inputs wake up that way.


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Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2004\01\22@085941 by Wouter van Ooijen

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> It would have been true if you hadn't snipped the very next
> sentence where I
> said that any pins that can be analog inputs wake up that way.

But IIRC that is only true for the 12/14 bits, not for the 18F (16 bit)?

Wouter van Ooijen

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2004\01\22@092018 by John Ferrell

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It does take code space but the only safe way is to initialize everthing
present as step one in your startup code.
John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
spam_OUTjohnferrellTakeThisOuTspamearthlink.net
http://DixieNC.US
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"

{Original Message removed}

2004\01\22@094203 by hael Rigby-Jones

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>-----Original Message-----
>From: John Ferrell [.....johnferrellKILLspamspam@spam@EARTHLINK.NET]
>Sent: 22 January 2004 14:23
>To: PICLISTspamKILLspamMITVMA.MIT.EDU
>Subject: Re: [PIC:] pin function defaults...
>
>
>It does take code space but the only safe way is to initialize
>everthing present as step one in your startup code. John

Are you saying that Microchips default register values at reset are
unreliable?  I've not had a problem initialising only the functions I use
and leaving the rest.  The brownout detect or watchdog timer should reset
everything to the state shown in the datasheets (apart from RCON obviously).

Mike




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2004\01\22@102611 by Olin Lathrop

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Wouter van Ooijen wrote:
> But IIRC that is only true for the 12/14 bits, not for the 18F (16
> bit)?

It is true for all PICs I have looked at, which include several 18F.  I'm
looking at the 18F6520 data sheet right now, and the ADCON1 register is
shown with initial value of 0 (page 214, DS39609A) which means maximum
number of analog inputs.

The reason is so that each pin wakes up in the most benign state from the
external circuit point of view.  Both analog and digital inputs would be
high impedence, but digital inputs can cause larger currents and undesirable
behaviour internally when held at intermediate voltages for long periods of
time.  Therefore waking up a pin as analog when there is a choice is safer.
It's no big deal since the code can easily configure it any way it wants to
once it starts running.


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Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2004\01\22@113400 by Mike Hord

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> > Actually, it's pretty simple.  When there is a choice, all peripherals
>off,
> > all pins are inputs.
>
>Not always true, look at the 628.  Perhaps it's always true that when there
>is a comparator it powers up as a comparator.

Also not always true.  On the 16F87xA's, the comparator's are NOT enabled
on power up.  This may be a special case, to maintain backwards
compatability
with the originals.

Mike H.

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2004\01\22@142449 by John Ferrell

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A lot of experience has taught me to not trust anyone or thing that I don't
have to. If the space is available, the change in boot time will not be
noticable and you will never know what trouble you missed...

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
EraseMEjohnferrellspam_OUTspamTakeThisOuTearthlink.net
http://DixieNC.US
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"

----- Original Message -----
From: "Michael Rigby-Jones" <Michael.Rigby-Jonesspamspam_OUTBOOKHAM.COM>
To: <@spam@PICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Thursday, January 22, 2004 9:41 AM
Subject: Re: [PIC:] pin function defaults...


> >{Original Message removed}

2004\01\22@144525 by Mike Harrison

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face
On Thu, 22 Jan 2004 14:27:00 -0500, you wrote:

>A lot of experience has taught me to not trust anyone or thing that I don't
>have to. If the space is available, the change in boot time will not be
>noticable and you will never know what trouble you missed...
>
>John Ferrell
>6241 Phillippi Rd
>Julian NC 27283
>Phone: (336)685-9606
>KILLspamjohnferrellKILLspamspamearthlink.net
>http://DixieNC.US
>NSRCA 479 AMA 4190  W8CCW
>"My Competition is Not My Enemy"
>
>----- Original Message -----
>From: "Michael Rigby-Jones" <RemoveMEMichael.Rigby-JonesTakeThisOuTspamBOOKHAM.COM>
>To: <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
>Sent: Thursday, January 22, 2004 9:41 AM
>Subject: Re: [PIC:] pin function defaults...
>
>
>> >{Original Message removed}

2004\01\22@211957 by William Chops Westfield

face picon face
On Thursday, Jan 22, 2004, at 07:25 US/Pacific, Olin Lathrop wrote:

> The reason is so that each pin wakes up in the most benign state from
> the
> external circuit point of view.  Both analog and digital inputs would
> be
> high impedence, but digital inputs can cause larger currents and
> undesirable
> behaviour internally when held at intermediate voltages for long
> periods of
> time.  Therefore waking up a pin as analog when there is a choice is
> safer.

Yes, this makes lots of sense.  But the sort of issue that I'm talking
about
is that it took me a while to discover that I had to configure the
comparator
rather than the A-D to get GP output to work right, and I'm still not
clear
WHY having the comparator in its default state interfered with digitial
output;
I just fiddled with things by trial and error till it worked right...
:-(

BillW

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