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'[PIC] Avdd left floating'
2008\10\15@231932 by Grant Brown

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face
Hi,

Is there any know issue with leaving the analogue pins Avdd and Avss
pins floating (not connected to anything).

Please note that the ADC section of the PIC32 is not used at all within
my program.

Avdd - Pin 30
Avss - Pin 31

--
Kind Regards
Grant Brown


2008\10\16@002501 by Vitaliy

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face
Grant Brown wrote:
> Is there any know issue with leaving the analogue pins Avdd and Avss
> pins floating (not connected to anything).
>
> Please note that the ADC section of the PIC32 is not used at all within
> my program.
>
> Avdd - Pin 30
> Avss - Pin 31

I'm not sure whether there is a downside or not, but I would connect them to
Vdd and Vss, respectively -- just to be safe.

Vitaliy

2008\10\16@015658 by Xiaofan Chen

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On Thu, Oct 16, 2008 at 12:14 PM, Grant Brown <spam_OUTgrantTakeThisOuTspamsitedoc.com.au> wrote:

> Is there any know issue with leaving the analogue pins Avdd and Avss
> pins floating (not connected to anything).

A lot of issues.
What is the problem to connect them to Vdd and Vss respectively?

Xiaofan

2008\10\16@021817 by Vitaliy

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face
Xiaofan Chen wrote:
>> Is there any know issue with leaving the analogue pins Avdd and Avss
>> pins floating (not connected to anything).
>
> A lot of issues.

Care to list? :-)


2008\10\16@024506 by Xiaofan Chen

face picon face
On Thu, Oct 16, 2008 at 2:16 PM, Vitaliy <.....spamKILLspamspam@spam@maksimov.org> wrote:
> Xiaofan Chen wrote:
>>> Is there any know issue with leaving the analogue pins Avdd and Avss
>>> pins floating (not connected to anything).
>>
>> A lot of issues.
>
> Care to list? :-)

Ok, let me start with a few possible outcomes.
1) How come the programming depends on the phase of the moon?
2) How come I can not enter debugging mode?
3) How come 4 out of the 10 units do not work?

There are more which will be left to you as an exercise. ;-)

Xiaofan

2008\10\16@025343 by Grant Brown

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Hi  Xiaonfan,

Because the board has already been etched with the pins floating

The board is a prototype anyway so this can be adjusted at some stage
latter.

Is it OK to tie them both to GND ?

This I can do with the prototype board without to any issues, however
connecting them to Vdd and Vss would be a problem especially given the
0.4 pitch.

If they are left as is - ie floating, what sort of issues can I expect ?

Kind Regards
Grant Brown



Xiaofan Chen wrote:
{Quote hidden}

--
Kind Regards
Grant Brown

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2008\10\16@033551 by Vitaliy

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Xiaofan Chen wrote:
>>>> Is there any know issue with leaving the analogue pins Avdd and Avss
>>>> pins floating (not connected to anything).
>>>
>>> A lot of issues.
>>
>> Care to list? :-)
>
> Ok, let me start with a few possible outcomes.
> 1) How come the programming depends on the phase of the moon?
> 2) How come I can not enter debugging mode?
> 3) How come 4 out of the 10 units do not work?
>
> There are more which will be left to you as an exercise. ;-)

I can think of a few more along the same lines:

4) Loss of hair and appetite.
5) Erections lasting longer than four hours.
6) Death, and other reproductive harm.

But seriously, are the ones you listed fact, or hearsay? How do you know?
Can anyone else confirm?

Vitaliy

2008\10\16@043952 by Xiaofan Chen

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On Thu, Oct 16, 2008 at 3:28 PM, Vitaliy <.....spamKILLspamspam.....maksimov.org> wrote:
> Xiaofan Chen wrote:
>>>>> Is there any know issue with leaving the analogue pins Avdd and Avss
>>>>> pins floating (not connected to anything).
>>>>
>>>> A lot of issues.
>>>
>>> Care to list? :-)
>>
>> Ok, let me start with a few possible outcomes.
>> 1) How come the programming depends on the phase of the moon?
>> 2) How come I can not enter debugging mode?
>> 3) How come 4 out of the 10 units do not work?
>>
>> There are more which will be left to you as an exercise. ;-)
>
> But seriously, are the ones you listed fact, or hearsay? How do you know?
> Can anyone else confirm?

I know it because it is in the programming specification. And I certainly have
done some enough ICSP testing to know it.

But you are always welcome to try out by yourself. ;-)

Xiaofan

2008\10\16@062450 by Jinx

face picon face
Is there any reason to *not* connect the analogue supply pins ?

Looking just at power management, non-connection of Avss / Avdd
is never mentioned as a way to save power. My inclination would be
to connect them to avoid the possibility of induced noise

A lot of technical advice in this pdf. Note the last sentence. As written,
it's ambiguous as to whether that means you can float the pins if they
stay within 0.3V of the corresponding digital supply pins or whether
they should be connected and within a 0.3V range. Personally I think
they should be connected. And filtered for best ADC results

http://ww1.microchip.com/downloads/en/AppNotes/00823a.pdf

Analog Design in a Digital World Using Mixed Signal Controllers

"A natural extension of the separate supply method is to separate the
power supplies of circuitry within a single device. The performance of
the PIC16C78X analog peripherals is significantly improved due to
the separation of the noisier digital supply from the analog supply within
the chip. A simple method for controlling noise in a PIC16C78X mixed
signal design is to maintain the separation of the power supplies outside
of the device: one for slower low current analog functions, and the
second for the faster medium current digital functions. Keep in mind that
the AVSS and VSS connections, as well as the AVDD and VDD
connections, must be kept within 0.3 volts of each other"

2008\10\16@080920 by olin piclist

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Grant Brown wrote:
> Is there any know issue with leaving the analogue pins Avdd and Avss
> pins floating (not connected to anything).

Only if you care that the PIC behave according to the datasheet.

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

2008\10\16@082558 by Grant Brown

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face
Hi Olin,

Yes thanks for that, helps a lot   =-O

But seriously given that the ADC section is not used anywhere in my
program will this cause a serious issue.

The board in question is a prototype so I can fix up the mistake when I
do the next board.

In saying issues, I was more concerned that I may damage the chip if I
power it up withe the Avdd & Avss pins floating.

Kind Regards
Grant Brown

Olin Lathrop wrote:
{Quote hidden}

--
Kind Regards
Grant Brown

SiteDoc Pty Ltd
mob: 0412 926 995
http://www.sitedoc.com.au
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2008\10\16@082705 by olin piclist

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Grant Brown wrote:
> Is it OK to tie them both to GND ?

No (Duh).  RTFM!

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

2008\10\16@084835 by Michael Rigby-Jones

picon face


> -----Original Message-----
> From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu] On
Behalf
{Quote hidden}

What package is the PIC in?  No possibility of simply linking the AVxx
pins to the supply pins with a couple of bits of Kynar insulated
(wirewrap) wire or enamelled copper wire?

Regards

Mike

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2008\10\16@085759 by Wouter van Ooijen

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> But seriously given that the ADC section is not used anywhere in my
> program will this cause a serious issue.

There is of course no guarantee that it will, just like there is no
guarantee that it won't. You are operating the chip way out of specs. As
far as Microchip is concerned it might as well start reciting Hamlet to
you, or start cold fusion.

I don't think it makes sense to press the piclisters for an answer: the
chance that anyone has tried this is very small, and if he was
successful that still does not prove much.

--

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu

2008\10\16@102045 by olin piclist

face picon face
Grant Brown wrote:
> In saying issues, I was more concerned that I may damage the chip if I
> power it up withe the Avdd & Avss pins floating.

But "emitting a puff of smoke and never working again" is valid behavior
when you run the PIC outside the specified limits.  I expect you'd call that
"damage".


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

2008\10\16@115959 by Vitaliy

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face
Wouter van Ooijen wrote:
> As
> far as Microchip is concerned it might as well start reciting Hamlet to
> you, or start cold fusion.

Niiiiiiiiiice.....  >:-D

2008\10\16@155658 by M. Adam Davis

face picon face
The responses you're getting may be somewhat frustrating, since I know
other microcontrollers allow you to disable certain sections by tying
their seperate power pins to ground.

In any case, you should not leave them floating.  This being CMOS
there are reasons, but the upshot is that floating pins are devious
(leakage currents induce undefined linear switching behavior which at
minimum consumes current, and worst initiates latchup and fries the
part - although most CMOS processes no longer are susceptable to
latchup, it's not something to be risked.

However, in this case the others are right.  The data sheet is very
explicit on this point - you HAVE to power the A/D module for correct
functioning of the chip:

Page 621 of the PIC32MX manual (61143e.pdf)

Device Supply -

AVdd minimum must be greater than 2.5V, or VDD - 0.3V (whichever is
higher).  (There's also a maximum, and a min and max for AVss)

So in no case can you power AVdd less than 2.5V, and you can only go
that low if Vdd is 2.8V or lower.

HOWEVER - if you contact microchip and ask them specifically they may
give you information about the internal architechture and proces that
tells you that the chip can be dealt with differently.  You cannot
depend on that always being the case - they only have to follow the
data sheet (except when they don't and then they only have to change
it or release an errata if caught).  So I wouldn't depend on it at
all, but it previous jobs I was expected to stress the parts in
elaborate ways to lower costs, contacting the manufacturers for this
sort of thing was expected, and the purchasers always made sure they
purchased the same mask rev parts.  I doubt it actually saved money in
the long run, but it looked good on the books, eh?

-Adam

On Thu, Oct 16, 2008 at 12:14 AM, Grant Brown <@spam@grantKILLspamspamsitedoc.com.au> wrote:
{Quote hidden}

> -

2008\10\18@201213 by Xiaofan Chen

face picon face
On Thu, Oct 16, 2008 at 3:28 PM, Vitaliy <KILLspamspamKILLspamspammaksimov.org> wrote:
> Xiaofan Chen wrote:
>>>>> Is there any know issue with leaving the analogue pins Avdd and Avss
>>>>> pins floating (not connected to anything).
>> Ok, let me start with a few possible outcomes.
>> 1) How come the programming depends on the phase of the moon?
>> 2) How come I can not enter debugging mode?
>> 3) How come 4 out of the 10 units do not work?
>
> But seriously, are the ones you listed fact, or hearsay? How do you know?
> Can anyone else confirm?

Just one example for Point 1. Point 2 is similar.
http://forum.microchip.com/tm.aspx?m=375655

Xiaofan

2008\10\19@190359 by Grant Brown

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face
Hi Xiaofan,

Shame you did not see fit to provide the link when the question was
first asked instead of all the rubbish you did provide.

I guess it must feel good for you to provide silly and frustrating
answers to those that are asking what seem to them genuine questions.

I have looked after many many apprentice's  over the year, I  find it
more constructive to provide them with proper answers to there
questions. They usually learn more that way.

Not all of use are as clever as you mate,

Grant


Xiaofan Chen wrote:
{Quote hidden}

--
Kind Regards
Grant Brown

SiteDoc Pty Ltd
mob: 0412 926 995
http://www.sitedoc.com.au
__________________________________________________________________________________________________________
This email message together with any attachments is intended only for the addressee(s) and contains information that may be confidential and/or copyright.  If you are not the intended recipient, please notify the sender by reply email (or telephone SiteDoc Pty Ltd on +61 2 42291185) and immediately delete this email together with any attachments from your computer. If you are the intended recipient, you must not copy, disclose, reproduce or distribute this communication together with any attachments without the authority of SiteDoc Proprietary Limited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. Unless specifically stated by the sender as the views of SiteDoc Proprietary Limited, any views expressed in this message are those of the individual sender, and no responsibility will be borne by SiteDoc Proprietary Limited for its content or outcomes.

2008\10\19@192952 by Xiaofan Chen

face picon face
On Mon, Oct 20, 2008 at 8:00 AM, Grant Brown <spamBeGonegrantspamBeGonespamsitedoc.com.au> wrote:
> Hi Xiaofan,
>
> Shame you did not see fit to provide the link when the question was
> first asked instead of all the rubbish you did provide.

If you thinks so. But never mind. Others can judge whether it is
appropriate or not.


Xiaofan

2008\10\20@001121 by William \Chops\ Westfield

face picon face

On Oct 19, 2008, at 5:00 PM, Grant Brown wrote:

> Shame you did not see fit to provide the link when the question was
> first asked instead of all the rubbish you did provide.

Sheesh.

1) The "answer" was the same as before: "don't do it."
2) Piclist is not a search engine, where you post your question
   and other people search for your answer.  Why didn't YOU search
   the Microchip forums before asking here?
3) The message that Xiafan provided a link to was from 18-oct, well
   AFTER the previous discussion was over.  Presumably he saw it
   while reading the Microchip forums and remembered it as a topic
   of interest here.  Service above and beyond the call of duty, if
   you ask me.

BillW

2008\10\20@003357 by Dr Skip

picon face
AGREED.

William "Chops" Westfield wrote:

>     Service above and beyond the call of duty, if
>     you ask me.
>
> BillW
>

2008\10\20@010305 by Grant Brown

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face
Hi William,

Your quite right mate, its not a search engine.

It is however a forum in which one may ask a question relating to the
PIC devices and expect a reasonable answer if indeed someone is kind
enough to provide one.

I asked what I thought was a reasonable question.

I did not however expect a stupid answer that was intended to be-little me.

A simple - thats not a good idea ..... would have sufficed

Grant


William "Chops" Westfield wrote:
{Quote hidden}

--
Kind Regards
Grant Brown

SiteDoc Pty Ltd
mob: 0412 926 995
http://www.sitedoc.com.au
__________________________________________________________________________________________________________
This email message together with any attachments is intended only for the addressee(s) and contains information that may be confidential and/or copyright.  If you are not the intended recipient, please notify the sender by reply email (or telephone SiteDoc Pty Ltd on +61 2 42291185) and immediately delete this email together with any attachments from your computer. If you are the intended recipient, you must not copy, disclose, reproduce or distribute this communication together with any attachments without the authority of SiteDoc Proprietary Limited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. Unless specifically stated by the sender as the views of SiteDoc Proprietary Limited, any views expressed in this message are those of the individual sender, and no responsibility will be borne by SiteDoc Proprietary Limited for its content or outcomes.

2008\10\20@011855 by Xiaofan Chen

face picon face
On Mon, Oct 20, 2008 at 2:00 PM, Grant Brown <TakeThisOuTgrantEraseMEspamspam_OUTsitedoc.com.au> wrote:
> Your quite right mate, its not a search engine.
>
> It is however a forum in which one may ask a question relating to the
> PIC devices and expect a reasonable answer if indeed someone is kind
> enough to provide one.
>
> I asked what I thought was a reasonable question.
>
> I did not however expect a stupid answer that was intended to be-little me.

I have no intention to be-little you. But if you felt that way,
I apologize.

> A simple - thats not a good idea ..... would have sufficed

The following is my reply.
>> Ok, let me start with a few possible outcomes.
>> 1) How come the programming depends on the phase of the moon?
>> 2) How come I can not enter debugging mode?
>> 3) How come 4 out of the 10 units do not work?
>
> There are more which will be left to you as an exercise. ;-)

I do not think the answer is stupid at all.

Anyway, enough for this thread.

Xiaofan

2008\10\20@040449 by Vitaliy

flavicon
face
Grant Brown wrote:
> I did not however expect a stupid answer that was intended to be-little
> me.

I'm sure that wasn't Xiaofan's intent at all.


> A simple - thats not a good idea ..... would have sufficed

I believe that's what you've been told, at the very beginning.


I've been reading some of your posts, and see that you've made a lot of
progress in a very short time. However, you may be suffering from PICList
poisoning. It is addictive, and too much of a good thing is a bad thing.
I've seen many people (Xiaofan and myself included) fall victim to it. The
best medicine is to take a break from the PICList for a few days.

Sincerely,

Vitaliy

2008\10\20@074556 by olin piclist

face picon face
Grant Brown wrote:
> It is however a forum in which one may ask a question relating to the
> PIC devices and expect a reasonable answer if indeed someone is kind
> enough to provide one.

For reasonable questions.  Questions that have been answered many times here
and on the microchip forum, or that are answered in the datasheet right
where you'd expect to find them are in the "not so brilliant" catagory.  If
you do that, be prepared for a gruff answer.

Then there are stupid questions we get all too often about what the PIC will
do when you violate the specifications.

If I remember right, yours was at least in the first catagory, and you kept
pushing and then it entered the second catagory.

> I asked what I thought was a reasonable question.

It wasn't, see above.

> I did not however expect a stupid answer that was intended to
> be-little me.

If you do something stupid publicly, you may get called on it publicly.
Stop whining and get over it.

> A simple - thats not a good idea ..... would have sufficed

If I remember right, the first responses were exactly that, which the
datasheet also tells you quite clearly.  But that didn't suffice.  You
wanted to know how much you could ignore the specs and get away with it.


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

2008\10\20@085044 by Michael Rigby-Jones

picon face


> -----Original Message-----
> From: RemoveMEpiclist-bouncesspamTakeThisOuTmit.edu [piclist-bouncesEraseMEspam.....mit.edu] On
Behalf
> Of Olin Lathrop
> Sent: 20 October 2008 12:46
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] Avdd left floating
>
>
> If you do something stupid publicly, you may get called on it
publicly.

Only by people that get a kick from belittling others.

> Stop whining and get over it.

Charming.  Some things never change.

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2008\10\20@125657 by Charles Rogers

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face


I AGREE ALSO ! ! !

CR



| AGREED.
|
| William "Chops" Westfield wrote:
|
| >     Service above and beyond the call of duty, if
| >     you ask me.
| >
| > BillW
| >
| --

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