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PICList Thread
'The unused 40pin socket on the PIC Start programme'
1994\06\15@072115 by IDH

'The unused 40 pin pickstart socket.'
1994\06\15@073342 by IDH

1994\06\15@074540 by byron

1994\06\15@080137 by rca

> spam_OUTbyronTakeThisOuTcc.gatech.edu (Byron A Jeff)
>
>>BTW can someone make the MPSTART.EXE software (V3.04) available to me?
>
>You can ftp it from ftp.sics.se in the pub/mchipsoft/picstrt16 directory or
similar.
>
>Hope that helps.
>
>Rafe
>

----------------------------------------------------------------
Rafe Aldridge - .....rcaKILLspam@spam@sirius.tn.rl.ac.uk
R65, Rutherford Appleton Lab,                      wwWWww
Chilton, Oxon, OX11 OQX, UK.                        o  o
------------------------------------------------ooO--(__)--Ooo--

'The unused 40 pin pickstart socket. '
1994\06\15@175723 by eric

1994\07\27@173253 by dpalmer

1994\07\28@000401 by dthomas

1997\10\21@182958 by ndie Ohtsji [4555]

Hi Steve,

I'm not too familiar with the 16C73 so whatever I say may be false
.... but I'm sure others will flame me if I'm wrong.

I assume you mean all the unused port pins.....if so then, make them
outputs and set them to a know state, then you don't have
to do anything......err you may want to check your data sheet
as some may have an open drain.  In this case you may want to set
them low instead of high....then you don't have to do anything.

If you want the outputs high (for whatever reason), some have internal
pullups you can enable.  For the open drain pin(s), you need to connect
a pullup.

If you make them inputs, then use pullups (10K) to prevent them from
floating around.

Regards,

-Randie

/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/*/
*/ Randie Ohtsji                                                     /*
/* Glenayre R&D, Vancouver, BC  CANADA   Phone: (604) 293-1611 x4555 */
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{Quote hidden}

> From .....sm66KILLspam.....HOTMAIL.COM Tue Oct 21 15:03:39 1997
> X-Originating-IP: [140.165.2.77]
> Date:         Tue, 21 Oct 1997 14:50:37 PDT
> From: stephen mcalonan <EraseMEsm66spam_OUTTakeThisOuTHOTMAIL.COM>
> Subject:      unused pins
> To: PICLISTspam_OUTMITVMA.MIT.EDU
>
> I am developing a small application around the PIC16C73.  Is there
> anything that I need to do with the unused pins (pullups, etc)?
> Thanks in advance,
> Steve McAlonan
>
> ______________________________________________________
> Get Your Private, Free Email at http://www.hotmail.com
>

1997\10\21@191758 by DREITEK

1997\10\21@194109 by John Payson

1997\10\25@094353 by paulb

1997\10\25@174612 by Harold M Hallikainen

1997\10\27@122242 by David W. Duley

'[OT] Unused parts in stock'
1997\12\22@033024 by Luis Fernandez

Hi list,

>> I have used it before with no purchasing problems, but when I
>> contacted my local distributor yesterday I was given a 16 week
>> lead time and told that Ramtron's lead times are extending all
>> the time.
>
>I have 40 piece of FM24C16-SO8 that I don't need anymore.  They are
>purchased 4 months ago not used yet.

Is there is any forum to buy/offer unused parts in stock. Probably many
times one needs something that others keep stocked with no plans to use.



Luis Fernandez Cormenzana
RadioBit Sistemas, S.L.
       Vehicle fleet control systems
       Patrol presence controllers

Fax/Tel:+34-6-585 64 57
       +34-6-680 26 33
e-mail: @spam@radiobitKILLspamdragonet.es
http://www.dragonet.es/users/radiobit

1998\04\15@182519 by Andrew Warren

Bob Blick <KILLspamPICLISTKILLspamMITVMA.MIT.EDU> wrote:

> I'm using a 16C74A with two analog inputs. ADCON1 is set 04h, so I
> actually have three analog inputs. Is it OK to use the extra analog
> pin as an output, as long as I set TRISA accordingly?

Bob:

Yes, it's ok... Just remember that the PORTx bit corresponding to
that pin will always read "0", so read-modify-write instructions to
that port (including "BSF" and "BCF" instructions) will make that
pin pull low.

-Andy

=== Andrew Warren - RemoveMEfastfwdTakeThisOuTix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499

1998\04\15@184257 by Sean Breheny

At 03:17 PM 4/15/98 -0800, you wrote:
>Bob Blick <spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU> wrote:
>
>> I'm using a 16C74A with two analog inputs. ADCON1 is set 04h, so I
>> actually have three analog inputs. Is it OK to use the extra analog
>> pin as an output, as long as I set TRISA accordingly?
>
>Bob:
>
>Yes, it's ok... Just remember that the PORTx bit corresponding to
>that pin will always read "0", so read-modify-write instructions to
>that port (including "BSF" and "BCF" instructions) will make that
>pin pull low.
>
>-Andy

Andy,

When you say "will make that pin pull low", you mean if and when it is set
to a digital output, right? In other words, that pin will not attempt to
output a low when it is configured as an ADC input.

Just making sure that my idea of how read-modify-write works is correct.

Thanks,

Sean


+--------------------------------+
| Sean Breheny                   |
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Phone(USA): (607) 253-0315

1998\04\15@193315 by Andrew Warren

Sean Breheny <RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU> wrote:

> >> I'm using a 16C74A with two analog inputs. ADCON1 is set 04h, so I
> >> actually have three analog inputs. Is it OK to use the extra analog
> >> pin as an output, as long as I set TRISA accordingly?
> >
> > Yes, it's ok... Just remember that the PORTx bit corresponding to
> > that pin will always read "0", so read-modify-write instructions to
> > that port (including "BSF" and "BCF" instructions) will make that
> > pin pull low.
>
> When you say "will make that pin pull low", you mean if and when it
> is set to a digital output, right?

   Right, Sean.

> In other words, that pin will not attempt to output a low when it
> is configured as an ADC input.

   Correct; if the pin's TRIS bit is set to "1" (input), it will not
   pull low (whether or not it's configured as an analog input via
   ADCON1).

   -Andy

=== Andrew Warren - fastfwdEraseME.....ix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499

1998\04\15@201435 by Bob Blick

On Wed, 15 Apr 1998, Andrew Warren wrote:
> Bob Blick <EraseMEPICLISTMITVMA.MIT.EDU> wrote:
> > I'm using a 16C74A with two analog inputs. ADCON1 is set 04h, so I
> > actually have three analog inputs. Is it OK to use the extra analog
> > pin as an output, as long as I set TRISA accordingly?
>
> Bob:
>
> Yes, it's ok... Just remember that the PORTx bit corresponding to
> that pin will always read "0", so read-modify-write instructions to
> that port (including "BSF" and "BCF" instructions) will make that
> pin pull low.

Good point. I imagine a BSF or BCF on that pin would be OK, but not on any
other pin on that port. I'll juggle them around so the rest will be
inputs. Thanks again!

-Bob

1998\04\15@231914 by Andrew Warren

Bob Blick <RemoveMEPICLISTEraseMEEraseMEMITVMA.MIT.EDU> wrote:

> > Yes, it's ok... Just remember that the PORTx bit corresponding to
> > that pin will always read "0", so read-modify-write instructions to
> > that port (including "BSF" and "BCF" instructions) will make that
> > pin pull low.
>
> Good point. I imagine a BSF or BCF on that pin would be OK, but not
> on any other pin on that port.

   Correct.

> I'll juggle them around so the rest will be inputs.

   Good idea.

   -Andy

=== Andrew Warren - RemoveMEfastfwdspam_OUTKILLspamix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499

1998\04\16@004134 by tjaart

Andrew Warren wrote:

> Bob Blick <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU> wrote:
>
> > > Yes, it's ok... Just remember that the PORTx bit corresponding to
> > > that pin will always read "0", so read-modify-write instructions to
> > > that port (including "BSF" and "BCF" instructions) will make that
> > > pin pull low.
> >
> > Good point. I imagine a BSF or BCF on that pin would be OK, but not
> > on any other pin on that port.
>
>     Correct.
>
> > I'll juggle them around so the rest will be inputs.
>
>     Good idea.

Another way around it is to use a shadow register for port a.If you want to change any output on
that port, you change it
in the shadow register. Load the shadow into port a, and
presto! No read-modify-write problems!

--
Friendly Regards

Tjaart van der Walt
EraseMEtjaartspamspamBeGonewasp.co.za

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1998\04\16@105546 by lilel

1998\04\16@165859 by Alex Torres

> From: Bob Blick <bobSTOPspamspam_OUTTED.NET>

> I'm using a 16C74A with two analog inputs. ADCON1 is set 04h, so I
> actually have three analog inputs. Is it OK to use the extra analog pin
as
> an output, as long as I set TRISA accordingly? I recall this is the case,
> and looking at the block diagram of the innards of the chip it looks like
> that's OK to do.

Yes, its work.
But don't try to use this pin as digital input!
You are always read "0", and not use BCF/BSF instruction - use a mirror
register.

==============
Alex Torres, Kharkov, Ukraine (exUSSR)
spamBeGonealtorSTOPspamEraseMEgeocities.com
2:461/28 FidoNet
http://www.geocities.com/SiliconValley/Lab/6311

1998\05\03@060300 by White Horse Design

At 03:33 03/05/98 -0400, you wrote:

>I am unfortunately using a 28 pin 16c63 dedicated to oscillating a single
>pin via hardware USART.  Quick additional other question:  Are there any
>other PICs available that have hardware USART?

PIC16C74A does, as do many others.

(And I'm not going to write them all down for you! Get a databook from your
nearest distributor!)

Regards

Adrian

WWW    WWW   Adrian Gothard
WWW WW WWW   White Horse Design
WWWWWWWWWW   +44-385-970009 (Mobile/SMS), +44-118-962-8913/4 (voice/fax)
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---
Developers of GPS satellite-based tracking systems

1998\05\03@065821 by Morgan Olsson

At 03:33 1998-05-03 -0400, you wrote:
>Piclisters!
>My next question deals with unused PIC I/O pins.  Should they be made
>either an input or output (software), left floating or tied to gnd or +5v?

As output.

(Floating input may cause input cirquit to draw current if between high and
low, and if you tie an input it might get damaged if there is any program
error that makes it an output)

/Morgan
/  Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \
\  EraseMEmrtEraseMEiname.com, ph: +46 (0)414 70741; fax +46 (0)414 70331    /

1998\05\03@111705 by David VanHorn

'Comparing PIC Features (was Unused I/O pins)'
1998\05\04@013621 by Michael Ghormley

1998\05\04@183834 by Eric Smith

Michael Ghormley <@spam@mikeg@spam@spam_OUTBLACKSAND.NS.COM> wrote:

> There is a nifty comparison chart of PIC's at:
>
>         http://www.brouhaha.com/~eric/pic/chips.html
>
> The ones with a UART have '*'s in the SCI column.  I find it handy.

Alas, it is rather dated.  These days I should just refer people to the
Microchip web page, as they finally have pretty good charts themselves.
(Click "PICmicro(tm) Devices" on the navigation bar on the left.)

Cheers,
Eric

1998\11\04@200858 by James Cameron

enpassant wrote:
> I read in a book somewhere that unused microchip pins should be
> grounded to prevent them from "floating".

I've seen that to.  Unused inputs I thought it said.  Outputs don't
float, but are driven.

> In the case of the PIC (16F84) should unused I/O pins and any other
> unused pins be tied to ground???

On the PIC 16F84, the only possible unused pins are I/O pins.  Set them
as outputs, and you will not need to attach them to anything.

The problem with grounding them is that your software may attempt to
raise them to a high level, in which case current may flow.

--
James Cameron                                      (spamBeGonecameronKILLspamstl.dec.com)

OpenVMS, Linux, Firewalls, Software Engineering, CGI, HTTP, X, C, FORTH,
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Disability Engineering, Netrek, Bicycles, Pedant, Farming, Home Control,
Remote Area Power, Greek Scholar, Tenor Vocalist, Church Sound, Husband.

"Specialisation is for insects." -- Robert Heinlein.

1998\11\04@200913 by Harold Hallikainen

On Wed, 4 Nov 1998 19:33:31 -0500 enpassant <.....enpassantspam_OUTAMERITECH.NET>
writes:
>I read in a book somewhere that unused microchip pins should be
>grounded
>to prevent them from "floating".  In the case of the PIC (16F84)
>should
>unused I/O pins and any other unused pins be tied to ground???  Being
>new with this stuff I'm not sure.  Thanks.
>

Unused input pins should not be allowed to float  (at mid-voltage the
chip draws more current).  For maximum flexibility, I program unused pins
as outputs, which can then be left unconnected.  I can then later decide
to use the pins without cutting wires or traces.

Harold



Harold Hallikainen
TakeThisOuTharold.....TakeThisOuThallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

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1998\11\04@201305 by Dmitry Kiryashov

'Unused PIC Pins tied to GROUND? - somewhat OT'
1998\11\05@085244 by Harrison Cooper

1998\11\06@123228 by John Payson

'Unused bits of I/O ports'
1998\11\24@023047 by aureo

1998\11\24@025128 by Regulus Berdin

1998\11\24@164739 by Tony Nixon

>
> As discussed few weeks ago, unused ports can be programmed as output


Just be careful when protoyping with I/O ports set as outputs because it
is easy to short wires/tracks/pins etc while experimenting.

The 16C84 is a pretty tough chip though.


--
Best regards

Tony

Multimedia 16F84 Beginners PIC Tools.

http://www.picnpoke.com
Email TakeThisOuTpicnpokeKILLspamspamcdi.com.au

1998\11\24@170129 by Octavio Nogueira

>Just be careful when protoyping with I/O ports set as outputs because it
>is easy to short wires/tracks/pins etc while experimenting.
>
>The 16C84 is a pretty tough chip though.
>
>
>--
>Best regards
>
>Tony

Yes they really are. I had one in my experimenter board and I
was testing something else and powered it with 12V for several
minutes. And it's still working great.

Octavio
==============================================
Octavio Nogueira - .....nogueiraRemoveMEpropic2.com ICQ# 19841898
  From the creator of ProPic,   ProPic 2  now much better
    New ProPic 2 homepage:    http://www.propic2.com
   PIC Programmer for Windows with down to earth price
==============================================

1998\11\24@193650 by Tony Nixon

Octavio Nogueira wrote:
> Yes they really are. I had one in my experimenter board and I
> was testing something else and powered it with 12V for several
> minutes. And it's still working great.

I've still got the 1st one I ever bought. I don't know how many times
I've used it to experiment with. I think I mentioned ages ago about how
it has been through just about everything except run over by a truck,
although I stepped on it once. I've even had to solder some new pins
onto it, but it still keeps a going.

I don't think I'd use it in a pacemaker project though ;-)

--
Best regards

Tony

Multimedia 16F84 Beginners PIC Tools.

http://www.picnpoke.com
Email RemoveMEpicnpokespamBeGonecdi.com.au

1998\11\24@214552 by Eduardo R.

1998\11\24@220835 by Brian Striggow

1998\11\25@052505 by Octavio Nogueira

>>>The 16C84 is a pretty tough chip though.
>
>>>Yes they really are. I had one in my experimenter board and I
>>>was testing something else and powered it with 12V for several
>>>minutes. And it's still working great.
>Octavio
>
>
>!!!!!!!Several minutes !!!!! WOW lucky man,it's really hard to believe it
>would be that way a second time 'cause  same  hapenned to me  12V just for
>several seconds and is gone forever to the trash can.
>
> Eddy

Yes it's true and I have it right in front of me not to allow me to lie. :-)

Octavio
==============================================
Octavio Nogueira - spamBeGonenogueira@spam@spam_OUTpropic2.com ICQ# 19841898
  From the creator of ProPic,   ProPic 2  now much better
    New ProPic 2 homepage:    http://www.propic2.com
   PIC Programmer for Windows with down to earth price
==============================================

1998\11\25@075523 by paulb

1998\11\25@132321 by Reginald Neale

'Re : Re: Unused bits of I/O ports'
1998\11\25@154219 by Spk41q

'Unused bits of I/O ports'
1998\11\30@190030 by Marc

1999\01\13@125748 by Dan Larson

1999\01\13@134729 by Ohtsji, Randie

Make them inputs, then you won't  burn up your PIC when you accidentally
drive them high (this happens...it's called Murphy).

Randie
TakeThisOuTrandie.ohtsjispamglenayre.com
ICQ:28273278


{Original Message removed}

1999\01\13@165320 by Tony Nixon

If you leave these pins set as inputs, then make sure you have pullup or
pull down resistors for them, or you will have floating inputs.

You may get some wierd problems.


--
Best regards

Tony

Multimedia 16F84 Beginners PIC Tools.
** NEW PicNPro Programmer and Port Interface **

http://www.picnpoke.com
Email picnpokeEraseMEcdi.com.au

1999\01\13@180943 by andre

1999\01\14@033707 by paulb

1999\01\16@121941 by dave vanhorn

'Unused PIC Pins - What to do with them?'
1999\01\16@213635 by Geoff Thornton

Piclisters I have been following the thread "Unused PIC Pins tied to
Ground - Input or output" with some interest as I am new to PICs, and admit
the thread has left me somewhat confused. What exactly is the recommended
procedure for dealing with uncommited PIC pins?


Regards Geoff :)
==================
RemoveMEgeoffEraseMEspam_OUTtechie.com

1999\01\16@223734 by paulb

1999\01\17@065033 by Andy Stephenson

Leave them unconnected.

Do not connect them to VDD or VSS.

If you have room / cost add a pull up or pull down res. You don't have to
fit them in the final unit, but if you suddenly need a switch input - it's
there waiting for you.

If you choose to leave the lines totally unconnected, set them as outputs
in your software.

By doing this, you give yourself room for manouver (...spelling?) to catch
any last minute fixes.

Just my ten cents.

Rgds...

...Andy
At 12:33 17/01/99 +1000, you wrote:
{Quote hidden}

>Piclisters I have been following the thread "Unused PIC Pins tied to
>Ground - Input or output" with some interest as I am new to PICs, and admit
>the thread has left me somewhat confused. What exactly is the recommended
>procedure for dealing with uncommited PIC pins?
>
>
>Regards Geoff :)
>==================
>@spam@geoffRemoveMEEraseMEtechie.com
>

1999\01\17@070941 by Gerhard Fiedler

1999\01\18@022809 by ruben

I always leave unused pins unconnected and configured as outputs. That way
it is easy to use them for something (mostly debugging) that wasn't planed
at the beginning. This, I think, is common practice. What I also do, and
have not seen mentioned here before, is to frequently read the value of the
outport and write it back. This way the pin won't be destroyed if it is
forced low when written high (short circuit to ground or something), instead
the pin state is switched to whatever it is forced to externaly.

{Quote hidden}

> Piclisters I have been following the thread "Unused PIC Pins tied to
> Ground - Input or output" with some interest as I am new to PICs, and admit
> the thread has left me somewhat confused. What exactly is the recommended
> procedure for dealing with uncommited PIC pins?
>
>
> Regards Geoff :)
> ==================
> EraseMEgeoff@spam@techie.com

==============================
Ruben Jvnsson
AB Liros Elektronik
Box 9124, 200 39 Malmv, Sweden
TEL INT +4640142078
FAX INT +4640947388
@spam@rubenspam_OUT.....2.sbbs.se
==============================

1999\01\18@122419 by Gabriel Gonzalez

Basically, leave them unconnected, but set them as outputs in software.

Gabriel

-----Original Message-----
From: Geoff Thornton <spamBeGonegeoffEraseMETECHIE.COM>
To: PICLISTspamBeGoneMITVMA.MIT.EDU <RemoveMEPICLIST@spam@spamBeGoneMITVMA.MIT.EDU>
Date: Saturday, January 16, 1999 7:31 PM
Subject: Unused PIC Pins - What to do with them?


>Piclisters I have been following the thread "Unused PIC Pins tied to
>Ground - Input or output" with some interest as I am new to PICs, and admit
>the thread has left me somewhat confused. What exactly is the recommended
>procedure for dealing with uncommited PIC pins?
>
>
>Regards Geoff :)
>==================
>.....geoff@spam@EraseMEtechie.com

1999\01\25@140300 by John Payson

1999\01\26@041557 by paulb

1999\01\26@084554 by ruben

Well, this trick has saved me many windowed PIC's when I am in the
breadboard stage of a new design. At the beginning of a new project
I usually start with only part of the complete circuit leaving me
a lot of unused I/O pins. When I have got the core of the software
working I add more hardware and software bit by bit until the whole
thing is finished. Between the first stage and the finished working
prototype is mostly a lot of testing and changing of both hardware
and software. Needless to say, it has happened more than once that
an unused or used output by accident has been connected to a low
impedance source. The read and write back, especially on unused I/O's
set as outputs, saves the PIC in this case.

Another case where the read and write back is useful is when doing
fault mode and effects analysis on some type of safety circuits. Here
it is sometimes required to test and document what is happening when
shorting every pin on one IC with every other pin on the same IC. The
read-modify-write has saved many circuits here. A current limiting
resistor wouldn't help much in this case.

Bad design philosophy, however, is to let glitches affect your program
flow. When reading I/O's I always make sure, by good circuit design,
hardware and/or software filters, that what is read is not a glitch.
(I can't say that I have ever seen a glitch affect an unused,
unconnected I/O pin set as an output anyway.)

Things to watch out for with read-modify-write:
High load on an output pin. If the load is so high that the voltage
on an high output pin is not higher than the pin is read back as low
it won't work.

Settling time. Especially with capacitive load.
If a portpin is changed and the output is read back before
it is settled there will be no change.


With these things in mind I will happily continue my
read-and-write-back scheme, which has saved me more than
it has caused me trouble.

{Quote hidden}

> Ruben Jvnsson wrote:
>
> > What I also do, and have not seen mentioned here before, is to
> > frequently read the value of the outport and write it back.
>
>   I would say you have not seen it mentioned before because most would
> consider it a Bad Thing.  It's a rather bizarre design philosophy to
> set outputs to match glitches, and the most important lesson learned
> about the PIC is to avoid read-modify-write operations like the plague!
>
> > This way the pin won't be destroyed if it is forced low when written
> > high (short circuit to ground or something), instead the pin state is
> > switched to whatever it is forced to externaly.
>
>   Good design focusses on making sure that will never happen.  If you
> think it *may* happen, you use current-limiting resistors.  You might
> perhaps read the port and if it is stuck opposite to what was written,
> TRIS it to an input and send out a fault message.
>
>   Otherwise, your suggested read may pick up a glitch and write the
> output wrongly so that it does the very thing you were trying to avoid.
> --
>   Cheers,
>         Paul B.
>

==============================
Ruben Jvnsson
AB Liros Elektronik
Box 9124, 200 39 Malmv, Sweden
TEL INT +4640142078
FAX INT +4640947388
.....rubenRemoveME2.sbbs.se
==============================

ruben ,
where you said
"What I also do, and
have not seen mentioned here before, is to frequently read the value of the
outport and write it back. This way the pin won't be destroyed if it is
forced low when written high (short circuit to ground or something), instead
the pin state is switched to whatever it is forced to externaly."

thats a good idea.
how do you do it .for 16f84 & 12c508
glen
*******
Ruben Jšnsson wrote:

{Quote hidden}

> I always leave unused pins unconnected and configured as outputs. That way
> it is easy to use them for something (mostly debugging) that wasn't planed
> at the beginning. This, I think, is common practice. What I also do, and
> have not seen mentioned here before, is to frequently read the value of the
> outport and write it back. This way the pin won't be destroyed if it is
> forced low when written high (short circuit to ground or something), instead
> the pin state is switched to whatever it is forced to externaly.
>
> > Piclisters I have been following the thread "Unused PIC Pins tied to
> > Ground - Input or output" with some interest as I am new to PICs, and admit
> > the thread has left me somewhat confused. What exactly is the recommended
> > procedure for dealing with uncommited PIC pins?
> >
> >
> > Regards Geoff :)
> > ==================
> > .....geoffSTOPspam@spam@techie.com
>
> ==============================
> Ruben Jvnsson
> AB Liros Elektronik
> Box 9124, 200 39 Malmv, Sweden
> TEL INT +4640142078
> FAX INT +4640947388
> rubenEraseME@spam@2.sbbs.se
> ==============================

1999\02\11@021954 by ruben

Hello Glen,

This is mostly taken care of automatically (even if You want it or not)
by the read/modify/write function of I/O pins of all PIC processors.
That is, when you modify a pin in a port by clearing or seting a bit, the
whole port byte is first read, the bit is updated and the whole byte is
written back to the port. When the port value is first read it is the
logical level on the pin that is read and not the output latch in the PIC.

If You have unused output pins in a port and want them to follow what ever they
are externaly forced to just make sure You update another bit in the
port often enough without explicitly seting the unused output bit. If no bit in
port is modified often enough this can be done by MOV PORT_X,f which reads
the portvalue and writes it back again. Any forced output pins will then
change state. Be ware, though, that this may have unwanted effects on used
IO pins which shouldn't be allowed to change it's state. To overcome this,
use a shadow register in ram for the port and whenever the portvalue is to
be updated, modify it first in the shadow register, read the portvalue,
mask off the used pins, OR the result with the shadow register (which
should have the unused bits set to 0) and write it back to the port.
This way only the unused pins will change their state to whatever they are
forced to externaly.

Good luck

{Quote hidden}

> ruben ,
> where you said
> "What I also do, and
> have not seen mentioned here before, is to frequently read the value of the
> outport and write it back. This way the pin won't be destroyed if it is
> forced low when written high (short circuit to ground or something), instead
> the pin state is switched to whatever it is forced to externaly."
>
> thats a good idea.
> how do you do it .for 16f84 & 12c508
> glen
> *******

==============================
Ruben Jvnsson
AB Liros Elektronik
Box 9124, 200 39 Malmv, Sweden
TEL INT +4640142078
FAX INT +4640947388
RemoveMErubenspamBeGone2.sbbs.se
==============================

'filling unused code space'
1999\02\16@141238 by Harold Hallikainen

On Mon, 15 Feb 1999 14:42:04 -0600 John Payson <spamBeGonesupercatKILLspam@spam@CIRCAD.COM>
writes:

>
>Note that on the 17Cxx parts, a blank program location corresponds
>to a CALL instruction, but on all the 12- and 14-bit parts it will
>leave the PC and related registers alone.
>

       Back when I did stuff with the MC6802, I filled all unused code
space (and initialized all RAM) to 0x3f, which was a "software
interrutp".  If the program counter ended up on one of these locations,
it would vector to the initialization code and restart the machine (the
SWI vector was set the same as the RESET vector in ROM).
       Is there a way to do something similar on the PIC (specifically a
16c61)?  It seems that perhaps high ROM locations could be filled with
nops, then the PC would just roll around to the reset vector.
       Is there a way in MPASM to tell it to fill unused ROM with a
specific instruction?

Harold



Harold Hallikainen
haroldspam_OUT@spam@hallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

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1999\02\16@142142 by dave vanhorn

1999\02\16@162519 by Gerhard Fiedler

1999\02\16@164210 by dave vanhorn

1999\02\16@171028 by Tony Nixon

> 16c61)?  It seems that perhaps high ROM locations could be filled with
> nops, then the PC would just roll around to the reset vector.

That probably isn't necessary in this scenario. If the chip is properly
blank tested before programming then 12 bit chips have FFF which is
XORLW 0xFF and 14 bit chips have 3FFF which is ADDLW 0xFF.
The same thing would happen.


--
Best regards

Tony

Multimedia 16F84 Beginners PIC Tools.
** NEW PicNPro Programmer and Port Interface **

http://www.picnpoke.com
Email spamBeGonepicnpoke@spam@cdi.com.au

1999\02\17@072018 by Alan Nickerson

"peed all over the data", Must be a technical term... :)

Alan

-----Original Message-----
From: dave vanhorn <RemoveMEdvanhornEraseMEKILLspamCEDAR.NET>
To: spamBeGonePICLISTspam_OUTRemoveMEMITVMA.MIT.EDU <.....PICLISTRemoveMEMITVMA.MIT.EDU>
Date: Tuesday, February 16, 1999 4:44 PM
Subject: Re: filling unused code space


>At 01:17 PM 2/16/99 -0800, Gerhard Fiedler wrote:
>>At 14:18 02/16/99 -0500, dave vanhorn wrote:
>>>Wouldn't JMP Start suffice (or whatever you call the beginning of your
>>>code), which is where the reset vector will take it anyway?
>>
>>why not leave it unprogrammed, as somebody suggested before (so you can
add
>>something in case you need it)? that's something like ADDLW FFh (on the
>>14bitters) and either it wraps around to reset, or you put a "jmp here"
>>endless loop at the end and let it get hit by the watch dog. which seems
to
{Quote hidden}

>>be the proper way to do it.
>
>Depends on the system, I can see leaving a block of codespace somewhere
>blank, but you aren't going to need inbetween routines, since you can't get
>there anyway.  Everything I work on at the moment is flash, so I'm not
>likely to need to go burn a single byte change anywhere, that would be more
>work than reloading the whole codespace.
>
>You may not have a watchdog.. Our financial systems don't. We determined
>that a watchdog couldn't possibly stop the processor before it peed all
>over the data, if it wanted to, and so we used JMP 0 equivalents to force a
>reset.
>

1999\02\17@094030 by dave vanhorn

1999\02\17@105353 by Alan Nickerson

I just thought it was funny.

-----Original Message-----
From: dave vanhorn <dvanhorn@spam@CEDAR.NET>
To: EraseMEPICLISTRemoveMESTOPspamMITVMA.MIT.EDU <RemoveMEPICLISTKILLspamTakeThisOuTMITVMA.MIT.EDU>
Date: Wednesday, February 17, 1999 9:42 AM
Subject: Re: filling unused code space


>At 07:19 AM 2/17/99 -0500, Alan Nickerson wrote:
>>"peed all over the data", Must be a technical term... :)
>
>
>Sorry, I try not to get too technical. :)
>

'Unused pins'
1999\02\18@204941 by Biswanath Dutta

1999\02\19@121502 by John Payson

1999\02\19@213122 by Biswanath Dutta

1999\02\20@023538 by Quentin

'filling unused code space'
1999\02\20@082411 by paulb

Alan Nickerson wrote:

> I just thought it was funny.

> From: dave vanhorn <spamBeGonedvanhorn@spam@CEDAR.NET>
>>> "peed all over the data", Must be a technical term... :)
>> Sorry, I try not to get too technical. :)

 We all did.

Harold Hallikainen wrote:

> Is there a way to do something similar on the PIC (specifically a
> 16c61)?  It seems that perhaps high ROM locations could be filled with
> nops, then the PC would just roll around to the reset vector.
> Is there a way in MPASM to tell it to fill unused ROM with a specific
> instruction?

 And I think we came to the conclusion that this was already done for
us.  Depending on the µC "core", the instructions "ADDLW -1" and
"XORLW -1" are about as close to a NOP as you'd need.  They cause no
branch, no port alterations, repeated execution simply decrements or
complements W respectively on each cycle and within 1mS (for 1000
instructions at 4MHz) you wind through the unused memory and hit the
*reset* entry point within one eighteenth of the watchdog timeout
interval.

 The comment that this may take "too long" to happen is a little na•ve
as it seems to me.  Something *real bad* has happened to the system to
get here, concerns that it may slow the system down are a little too
late!

 So you can forget it.  Just make sure that the reset code iniitialises
all things that need initialisation, or if you like, code the very last
location with "GOTO $" (or variations involving page select) and let the
WDT run out.
--
 Cheers,
       Paul B.

Greetings All:
Today's Question
What is the best way to treat unused pins on a PIC for absolutely lowest
possible power consumption? (and the theory behind your choice please).

Options are:    output, drive hi, no termination
               output, drive lo, no termination
               input with pullup
               input with pulldown
               input floating (not really an option--pin will oscillate sometim
es)

Some thoughts from my end:
1. Inputs require a pull-up or -down resistor, possibly in the megohm
range, but still some current flow, plus an extra part.
2. Outputs don't require external parts, but with big ground planes and
potential board leakage, driving low might be the best.  However, most of
the programmers I have used tend to drive the pins hi.

So What is the consensus?
kelly
****************************************************************************
********
All legitimate attachments to this email will be clearly identified in the
text.
William K. Borsum, P.E.
OEM Dataloggers and Instrumentation Systems
<RemoveMEborsumspam_OUTdascor.com> & <http://www.dascor.com>

1999\06\11@153210 by Jamil J. Weatherbee

I talked to microchip tech support at one time about this, there really is
no concensus, because if your device is held in reset all the pins are in
tristate so i suppose it could draw lots of power.

The most economical, and safe from a software perspective seems to be just
configuring them as outputs.  Next to that probably putting a 100k
resistor to ground and configuring as outputs with latches low.  The 100k
resistors take care of having a tristate input during reset/input during
startup.



On Fri, 11 Jun 1999, William K. Borsum wrote:

> Greetings All:
> Today's Question
> What is the best way to treat unused pins on a PIC for absolutely lowest
> possible power consumption? (and the theory behind your choice please).
>
> Options are:    output, drive hi, no termination
>                 output, drive lo, no termination
>                 input with pullup
>                 input with pulldown
>                 input floating (not really an option--pin will oscillate somet
imes)
{Quote hidden}

>
> Some thoughts from my end:
> 1. Inputs require a pull-up or -down resistor, possibly in the megohm
> range, but still some current flow, plus an extra part.
> 2. Outputs don't require external parts, but with big ground planes and
> potential board leakage, driving low might be the best.  However, most of
> the programmers I have used tend to drive the pins hi.
>
> So What is the consensus?
> kelly
> ****************************************************************************
> ********
> All legitimate attachments to this email will be clearly identified in the
> text.
> William K. Borsum, P.E.
> OEM Dataloggers and Instrumentation Systems
> <borsumspamdascor.com> & <http://www.dascor.com>
>

'How to Set Unused Pins for VERY low power apps?'
1999\06\11@161358 by William K. Borsum

This brings up another question:
For inputs that occasionally have external inputs plugged in, but are
otherwise normally disconnected from external voltages, should the default
be pull-UP or pull-DOWN resistors on the input pins?  Again, the object is
to absolutely minimize power draw. Based on the arguments below, a
pull-down might seem best--assuming the external voltage sources and the
PIC code don't care.

Any more thoughts?



{Quote hidden}

>I talked to microchip tech support at one time about this, there really is
>no concensus, because if your device is held in reset all the pins are in
>tristate so i suppose it could draw lots of power.
>
>The most economical, and safe from a software perspective seems to be just
>configuring them as outputs.  Next to that probably putting a 100k
>resistor to ground and configuring as outputs with latches low.  The 100k
>resistors take care of having a tristate input during reset/input during
>startup.

>> Greetings All:
>> Today's Question
>> What is the best way to treat unused pins on a PIC for absolutely lowest
>> possible power consumption? (and the theory behind your choice please).
>>
>> Options are:    output, drive hi, no termination
>>                 output, drive lo, no termination
>>                 input with pullup
>>                 input with pulldown
>>                 input floating (not really an option--pin will oscillate

sometimes)
>>
>> Some thoughts from my end:
>> 1. Inputs require a pull-up or -down resistor, possibly in the megohm
>> range, but still some current flow, plus an extra part.
>> 2. Outputs don't require external parts, but with big ground planes and
>> potential board leakage, driving low might be the best.  However, most of
>> the programmers I have used tend to drive the pins hi.

****************************************************************************
********
All legitimate attachments to this email will be clearly identified in the
text.
William K. Borsum, P.E.
OEM Dataloggers and Instrumentation Systems
<spam_OUTborsumspam_OUTspam_OUTdascor.com> & <http://www.dascor.com>

1999\06\11@182130 by Jamil J. Weatherbee

To support the pull-down resistor argument
on my 16c73a the Vol is 0.6V max wheras Voh is Vdd-0.7V
i think this would be because of differences in the complementary fets in
the totem pole outputs.

so a pull down resistor with 0.6v would consume 15% less power than the
same resistor used as a pullup



On Fri, 11 Jun 1999, William K. Borsum wrote:

{Quote hidden}

> This brings up another question:
> For inputs that occasionally have external inputs plugged in, but are
> otherwise normally disconnected from external voltages, should the default
> be pull-UP or pull-DOWN resistors on the input pins?  Again, the object is
> to absolutely minimize power draw. Based on the arguments below, a
> pull-down might seem best--assuming the external voltage sources and the
> PIC code don't care.
>
> Any more thoughts?
>
>
>
> >I talked to microchip tech support at one time about this, there really is
> >no concensus, because if your device is held in reset all the pins are in
> >tristate so i suppose it could draw lots of power.
> >
> >The most economical, and safe from a software perspective seems to be just
> >configuring them as outputs.  Next to that probably putting a 100k
> >resistor to ground and configuring as outputs with latches low.  The 100k
> >resistors take care of having a tristate input during reset/input during
> >startup.
>
> >> Greetings All:
> >> Today's Question
> >> What is the best way to treat unused pins on a PIC for absolutely lowest
> >> possible power consumption? (and the theory behind your choice please).
> >>
> >> Options are:    output, drive hi, no termination
> >>                 output, drive lo, no termination
> >>                 input with pullup
> >>                 input with pulldown
> >>                 input floating (not really an option--pin will oscillate
> sometimes)
> >>
> >> Some thoughts from my end:
> >> 1. Inputs require a pull-up or -down resistor, possibly in the megohm
> >> range, but still some current flow, plus an extra part.
> >> 2. Outputs don't require external parts, but with big ground planes and
> >> potential board leakage, driving low might be the best.  However, most of
> >> the programmers I have used tend to drive the pins hi.
>
> ****************************************************************************
> ********
> All legitimate attachments to this email will be clearly identified in the
> text.
> William K. Borsum, P.E.
> OEM Dataloggers and Instrumentation Systems
> <borsumspam_OUTdascor.com> & <http://www.dascor.com>
>

'How to Setting Unused Pins ver VERY low power apps'
1999\06\12@022030 by Ernie Murphy

Another 2 cents worth...

 The project currently on my bench will have such an unused input in some
configurations, hence I've been musing about this. Here are the 6 (well, 8)
choices:

1) input, no resistor:  Bad, bad, very bad. Oscillation isn't really the
problem here (who cares how an unused pin changes), but the possibility it
will drift to Vcc/2 and hence turn on 2 fets from rail to rail is the scary
thing.

2) input with pull-up: OK, make the pullup the largest value you dare. Megs
would be OK in most enviroments. Dissipation will be practically zero.

3) input with pull-down: same as pull-up.

4) output no resistor: zero component count. Again no disipation for either
output state. Only danger is if the board is somehow shorted pin to pin. If
this is possible, perhaps one would use the same hi or lo state as the
adjacent pins to minimize uncontrolled short current.

5) output with pulldown: Adds a component for no reason. A high value
resistor will of cource be chosen... which is in parallel with the low
impeadance output stage... in the equivalent circuit the resistor drops
out. So why use it?

6) output with pullup: same as #5

I'm of course assuming a pulled-up output will be driven high, and
pulled-down driven low (ah, there are numbers 7 & 8). To cross these is to
just waste power. Incidentally, pulling up a high output will disipate zero
current, as the output only has its .7 drop from the rail IF there is
current being pulled out of it. No current, no drop. High outputs source
current, not sink it.

My choice is #4, output with no resistor. Since my free pin is next to the
ground pin, thats where I nailed it... output in the zero state.




At 12:24 PM 6/11/99 -0700, you wrote:
>Greetings All:
>Today's Question
>What is the best way to treat unused pins on a PIC for absolutely lowest
>possible power consumption? (and the theory behind your choice please).
>
>Options are:    output, drive hi, no termination
>                output, drive lo, no termination
>                input with pullup
>                input with pulldown
>                input floating (not really an option--pin will oscillate
sometimes)
{Quote hidden}

>
>Some thoughts from my end:
>1. Inputs require a pull-up or -down resistor, possibly in the megohm
>range, but still some current flow, plus an extra part.
>2. Outputs don't require external parts, but with big ground planes and
>potential board leakage, driving low might be the best.  However, most of
>the programmers I have used tend to drive the pins hi.
>
>So What is the consensus?
>kelly
>****************************************************************************
>********
>All legitimate attachments to this email will be clearly identified in the
>text.
>William K. Borsum, P.E.
>OEM Dataloggers and Instrumentation Systems
><RemoveMEborsumKILLspam@spam@dascor.com> & <http://www.dascor.com>
>
>

1999\07\14@115044 by Michael Rigby-Jones

1999\07\14@120513 by Andy Kunz

At 04:44 PM 7/14/99 +0100, you wrote:
>> I'm striving with a very common problem: fitting
>> a BIG program in a tight space. Seems a common one, right ? :-)
>>
>> I'm using the CCS compiler v2.666.
>>

HOOO HOOO!!!!!

Say, that's only about 400 revisions since I gave up on it (seriously).

Andy

==================================================================
Andy Kunz               Life is what we do to prepare for Eternity
------------------------------------------------------------------
andyspamBeGone.....rc-hydros.com      http://www.rc-hydros.com     - Race Boats
KILLspamandy.....montanadesign.com  http://www.montanadesign.com - Electronics
==================================================================

1999\07\15@005940 by Darrell Flenniken

'CCS and unused fragments'
1999\07\15@022806 by Antonio Pasini

Output drive High or Low depending on what they are attached to. I just did
a project where we were using the pin as an input to look for a slow
transition (analog ramp) and the power consumption was much higher when the
port was an input. I set it to output for lower power and switched to input
to test then back to output to reduce power.


At 12:24 PM 6/11/99 -0700, you wrote:
>Greetings All:
>Today's Question
>What is the best way to treat unused pins on a PIC for absolutely lowest
>possible power consumption? (and the theory behind your choice please).
>
>Options are:    output, drive hi, no termination
>                output, drive lo, no termination
>                input with pullup
>                input with pulldown
>                input floating (not really an option--pin will oscillate
sometimes)
{Quote hidden}

>
>Some thoughts from my end:
>1. Inputs require a pull-up or -down resistor, possibly in the megohm
>range, but still some current flow, plus an extra part.
>2. Outputs don't require external parts, but with big ground planes and
>potential board leakage, driving low might be the best.  However, most of
>the programmers I have used tend to drive the pins hi.
>
>So What is the consensus?
>kelly
>****************************************************************************
>********
>All legitimate attachments to this email will be clearly identified in the
>text.
>William K. Borsum, P.E.
>OEM Dataloggers and Instrumentation Systems
><spam_OUTborsumKILLspamdascor.com> & <http://www.dascor.com>
>
>

Larry G. Nelson Sr.
RemoveMEL.NelsonRemoveMEEraseMEieee.org
http://www.ultranet.com/~nr

1999\10\26@092449 by jamesp

1999\10\26@102319 by paulb

1999\10\26@140322 by Dave VanHorn

1999\10\26@205555 by Roberto Fernandes T Neto

1999\10\27@093014 by eplus1

The safest thing to do is to tie all unused pins to either ground or the
positive supply voltage using resistors, and leave them tri-stated (if they
are programmable i/o). Anything from about 1K to about 10K will work fine.
This way, if the pins get set to an unintended state (due to software bugs
or electrical noise or whatever), the chip will not be damaged because the
current will be limited by the resistor.

You could get rid of the resistors by just leaving the pins unconnected and
set as outputs, (high or low) but this leaves the possibility of the pins
floating while the chip is initializing, or in a fault situation in which
the pins are tristated unintentionally. It also introduces the (low but
real) possibility of the pin being shorted to the other supply rail and
causing functional failure or damage to the chip or supply.

The important thing is to avoid having a tri-stated (input) pin floating,
and to avoid having an output pin driven against an external connection so
that it exceeds its rated source/sink capability (or the combined
source/sink capability of the chip). Pull up or pull down resistors
eliminate both possibilities in all conditions. The worst than can happen is
accidentally driving an output against a pull up/down and thus wasting
power.

James Newton KILLspamjamesnewtonspamBeGonegeocities.com phone:1-619-652-0593
http://techref.homepage.com NOW OPEN (R/O) TO NON-MEMBERS!
Members can add private/public comments/pages ($0 TANSTAAFL web hosting)
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{Original Message removed}

1999\10\27@134440 by paulb

1999\10\27@171449 by eplus1

Paul, I respect your opinions (and you are more than welcome to sign up on
my TechRef and post them along side mine) and I won't refer to them as
"rubbish" or "ludicrous" but,

1. Accidental grounding or energizing of an output pin (via a dropped pen or
paperclip, ill-formed trace, bent component lead, etc...) to the opposite
rail CAN smoke the chip and is far more likely (especially in the hands of a
newbie) than any other serious error. Yes, since most projects have more
used than unused pins, a short is more likely to happen to an in-use output
pin but, given equality in other areas, why increase the chance?

2. The cost of the resister is minimal to the projects that beginning PICers
will be turning out. Experienced production personnel, like yourself, can
weight the pros and cons and most likely already have decided to do FOR
THEMSELVES. A large value resistor, even left in place, will not prevent the
pin from being used if the production boards need a feature added by hand
later. I am trying to give the SAFEST advice possible for beginners here.
More than enough people will pressure them not to "waste" resistors.

3. Many low power PIC applications involve the chips power cycling,
sometimes rapidly. The power loss due to rapid switching of a tri-stated
input pin may be significant. I would like hard data also. No, rapid
switching will not fry the chip, and I didn't say it would.

4. By using very large value resistors (as I recommended), the current draw,
even if the pin is incorrectly set, will be negligible. A 100M resistor at 5
volts is 50nA IF set incorrectly. I have seen power consumption increase by
50mA when the pull-ups were removed from an unused port on an old Z80/PIO
project. Now, that was an old TTL (I think) PIO and there was a lot of RF
noise on that board so I doubt anything that extreme would happen on a
little PIC thing today. Data on PICs would be nice.

I also have another hidden reason for recommending the resistor that you
have, almost, hit upon. I have found that the last minute design change or
feature addition is the rule rather than the exception. I ALWAYS allocate
space to bring out every pin used or not. Getting inexperienced people in
the habit of placing that resistor makes them better prepared for the
reality of EE life. I know that on many occasions, people that I have
mentored have related that a last minute change was eased because they were
able to replace the resistor with another component or wire in a jumper to
satisfy the unforeseen need.

If non of that is compelling (and I doubt it is from your point of view),
may we agree to disagree and let each decide for themselves without getting
personal?

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{Original Message removed}

1999\10\27@182313 by Dave VanHorn

1999\10\27@193333 by Robert A. LaBudde

<x-flowed>At 05:22 PM 10/27/99 -0500, Dave wrote:
>That being said, I would still put a resistor to ground on the schematic,
>and not populate it, so that later, you can add things to those pins, using
>the resistor pads.

After watching all of this discussion, I have come to a personal conclusion
(as a neophyte, I admit) that the best solution appears to be to set all
unused pins to output HIGH with 10k pull-up resistors. This apparently has
the following benefits:

1. Defined state & non-floating.
2. No current flow (since at HIGH with pull-up).
3. Ready for future use on board.
4. Pull-up resistors are weak enough to overcome when used for a purpose.


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</x-flowed>

1999\10\27@215018 by Tony Nixon

> > The important thing is to avoid having a tri-stated (input) pin
> > floating,
>
>   This is ludicrous!  So it might add a few dozen microamps to the
> current draw.  Not half as much as if your suggested pull-up resistor
> is accidentally pulled down by the same circumstance.

I don't think the current flow is the main problem here. A floating
input WILL cause erratic chip operation. Maybe not while you force it
to, but at some stage it will. I've had chips do all sorts of wierd
things, until I eliminated a floating pin (or pins). Some of these chips
froze just by placing a finger near them, some won't start, some start
but run 'funny'. The worst problem is spending mutitudes of time finding
out 'why', when you haven't realised the floating pin is the culprit. As
far as I know, the excess currents are caused by input FETS not knowing
what to do and the 'hi' and 'lo' ones turning on at the same time
causing minute rail to rail shorts, which could be at any frequency.
Surely this causes wonderful things to happen inside the die, false
triggering the brown out detect etc. - who knows?.

My opinion, is that there is some credibillity in using a moderate value
resistor to 'babysit' unused pins. Besides, there is your pin pad for
other uses if need be :-)


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1999\10\28@004140 by paulb

1999\10\28@110201 by eplus1

Yeah, I brain farted on the resistor values. I have a big box of 4.7k that I
use when I need such a thing. Truth is, Paul is right FOR THE PIC in that I
program unused pins for output and set them low. I DO always leave space for
a pad or a resistor for unexpected additions (especially post-production)
and if I were working with chips that I wasn't absolutely sure were going to
survive a short, I would use the resistors.

I also worry about my designs freaking on power-up before I can set the
unused pins for output. I haven't had the problems that Tony mentions with
erratic operation but if a production part started exhibiting that effect, I
would have a space on the board for the resistors to be added as a fix.

So, when answering a newbie question, I always advise the resistors. I still
think its the safest single answer.

I was asked off list if its ok to tie the pins together and use just one
resistor. My response was:
The safest thing to do is to use a separate resistor to a rail for each pin.
The next safest thing to do is to not use the resistors at all and program
the pins as outputs.
The least safest thing would be to tie the pins together and use one
resistor to a rail as it would be very easy to get two pins programmed as
outputs and one set high while the other was set low.

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{Original Message removed}

I am developing an application for the PIC12C672.  If the program counter
somehow winds up pointing to an unused area of program memory, I want to
make sure the watchdog timer will time out and issue a microcontroller reset
signal.

In their literature, Microchip suggests filling the unused memory with a
'GOTO $' command.  If the program counter is corrupted, it's likely this
instruction will execute until a watchdog time-out re-initializes the
microcontroller.  Microchip suggests this can be accomplished using the
MPASM command FILL with the following syntax (assuming the last location is
3FFH):

FILL (GOTO $), (400H-$)

Does anyone know a way to fill unused program memory with an assembly 'GOTO
$' using a Hi-Tech C compiler directive?

In addition, feel free to suggest other methods of forcing a watchdog
time-out reset in the event that the program counter goes wild.

Thanks in advance,
Kevin

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2000\09\13@160713 by Andrew E. Kalman

Re:

>
>Does anyone know a way to fill unused program memory with an assembly 'GOTO
>$' using a Hi-Tech C compiler directive?

memset() is part of PIC C, However, it doesn't work in bank2 and bank3.

Here's what I use to clear a structure in any bank:

char n;
structureType * structP;

n = sizeof(structureType);
structP = instanceofstructure;
while (n--);
  *structP++ = '\0';

so you can replace the '\0' with whatever a GOTO $ assembles to.


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2000\09\13@200619 by Plunkett, Dennis

2000\09\13@200834 by Plunkett, Dennis

2000\09\13@232315 by Andrew E. Kalman

Oops.

I wrote:


>char n;
>structureType * structP;
>
>n = sizeof(structureType);
>structP = instanceofstructure;
>while (n--);
>   *structP++ = '\0';
>
>so you can replace the '\0' with whatever a GOTO $ assembles to.

But of course that's my _RAM_ initializer, and will do nothing for ROM. Sorry.
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2001\01\14@090241 by mike

2001\01\14@111508 by Olin Lathrop

>>
Do unused inputs really need to be connected to ground?
What is the effect if they are not grounded?
Does it affect operation of the PIC?
<<

This has been beaten to death several times.  Check the archive.

I leave unused pins open and set them as outputs.  I usually tie unused
input-only pins to ground.


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2001\01\14@124041 by David VanHorn

2001\01\14@125936 by Dan Michaels

2001\01\14@152445 by Olin Lathrop

> To be "safe", it is best to tie unused input pins to ground [or Vcc,
> doesn't much matter which] *ONLY* through a resistor, rather than
> directly with a short. This is not superstition, as during code
> development it is all too easy to accidentally configure a pin
> intended as input to output. You then run the risk of
> short-circuiting an output.

Perhaps in a low volume product.  I wouldn't want to burden a high volume
product with unnecessary parts for a minor debugging convenience.


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2001\01\14@175023 by Dan Michaels

2001\01\15@151904 by Dwayne Reid

At 05:50 PM 1/14/01 -0500, Dan Michaels wrote:

>Even in a high volume product, personally I would never simply
>(a) configure a pin as output and then leave it unterminated, or
>(b) set a pin to input and then short straight it to gnd. There are
>a number of possible "disastrous" scenarios this way:
>
>1 - with (a), an ESD spike might modify the TRIS register, set an
>     output pin to input, and then it would float and pick up noise,
>     and possibly affect proper operation.

Hi there, Dan.

I would agree with your reasoning above *if* I set the TRIS registers only
at the start of code and never touched them again.  But I consider that to
be bad practice.  I refresh all important registers regularly, usually in
the routine that looks after the watchdog timer.  In fact, I will often
*read* the registers to make sure that it is what I expect them to be,
rather than just refreshing them.  If I get a nasty transient that is
enough to disturb the TRIS or INTCON registers, I figure that I had better
re-init everything anyways.  So: I configure un-used pins as output and set
them LO.

Regarding being able to use some of those un-used pins for later changes,
you are correct in that having pads with holes makes those changes easier
to make.  But you don't need to stuff components in those holes.

dwayne



Dwayne Reid   <EraseMEdwaynerSTOPspamRemoveMEplanet.eon.net>
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2001\01\15@155730 by David VanHorn

>
>I would agree with your reasoning above *if* I set the TRIS registers only
>at the start of code and never touched them again.  But I consider that to
>be bad practice.  I refresh all important registers regularly, usually in
>the routine that looks after the watchdog timer.  In fact, I will often
>*read* the registers to make sure that it is what I expect them to be,
>rather than just refreshing them.  If I get a nasty transient that is
>enough to disturb the TRIS or INTCON registers, I figure that I had better
>re-init everything anyways.  So: I configure un-used pins as output and set
>them LO.


Interesting.
I see what you mean here.
On the AVR or Z8, this isn't a problem because the tris-equivalent
registers can't be modified by inputs like this.  I can easily output a 1
into a short to ground (pointless but harmless) and the chip won't decide
to change it on me.

I think the PIC architecture puts a larger burden on you to protect the
processor from output forcing in your designs.

It's an interesting design wrinkle though, that your output bits could be
changed on you at any time. That, plus the weaknesses in the BSF/BCF
instructions wrt pin loading, argue twoard the shadow register approach for
the port registers.

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2001\01\15@192135 by Dan Michaels

Dwayne Reid wrote:

>I would agree with your reasoning above *if* I set the TRIS registers only
>at the start of code and never touched them again.  But I consider that to
>be bad practice.  I refresh all important registers regularly, usually in
>the routine that looks after the watchdog timer.


Also a good idea - back when I worked with 6805, Motorola actually
recommended in their databooks to periodically refresh the TRIS
registers [whatever they called them], just in case they are
changed by ESD/noise/etc. This should be easy to do in the outermost
code loop, since the TRIS are usually set on bootup and rarely changed,
in most cases.

- danM

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2001\01\15@194035 by Dwayne Reid

At 03:55 PM 1/15/01 -0500, David VanHorn wrote:

>Interesting.
>I see what you mean here.
>On the AVR or Z8, this isn't a problem because the tris-equivalent
>registers can't be modified by inputs like this.

Hi there, Dave.

Something you wrote puzzles me - maybe there is yet another PIC wrinkle
that I am not aware of.  Is there any condition where the TRIS register can
be changed by something happening on the port pins?  If so, this is a new
problem to me!

The only port related problem I can think of right now is the
read-modify-write issue - its not a problem since I am aware of it.  But I
am not aware of a TRIS register susceptibility.  Is there a problem
there?  What causes it and what does it do?

I always check or refresh TRIS and other important registers simply because
I can't predict what a nasty ESD or EMI event might do to me - all I can do
is deal with the problem if it happens.  But it sure doesn't happen during
normal operation.

dwayne




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2001\01\15@214016 by David VanHorn

At 05:10 PM 1/15/01 -0700, Dwayne Reid wrote:
>At 03:55 PM 1/15/01 -0500, David VanHorn wrote:
>
>>Interesting.
>>I see what you mean here.
>>On the AVR or Z8, this isn't a problem because the tris-equivalent
>>registers can't be modified by inputs like this.
>
>Hi there, Dave.
>
>Something you wrote puzzles me - maybe there is yet another PIC wrinkle
>that I am not aware of.  Is there any condition where the TRIS register can
>be changed by something happening on the port pins?  If so, this is a new
>problem to me!

Sorry, I meant port not tris :)

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2001\01\16@014433 by yansong gu

2001\01\21@222546 by Richard Sloan

Does not seem to matter if an unused output is fried.

-----Original Message-----
From: pic microcontroller discussion list
[PICLISTKILLspamEraseMEMITVMA.MIT.EDU]On Behalf Of Olin Lathrop
Sent: Sunday, January 14, 2001 3:19 PM
To: EraseMEPICLIST@spam@@spam@MITVMA.MIT.EDU
Subject: Re: [PIC]: grounding unused inputs


> To be "safe", it is best to tie unused input pins to ground [or Vcc,
> doesn't much matter which] *ONLY* through a resistor, rather than
> directly with a short. This is not superstition, as during code
> development it is all too easy to accidentally configure a pin
> intended as input to output. You then run the risk of
> short-circuiting an output.

Perhaps in a low volume product.  I wouldn't want to burden a high volume
product with unnecessary parts for a minor debugging convenience.


*****************************************************************
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(978) 772-3129, @spam@olinspamKILLspamembedinc.com, http://www.embedinc.com

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2001\01\22@041944 by Russell McMahon

I will have several unused pins on my 16F877

Should the unused pins be set as inputs or outputs and should they be tied
directly to GND or do I use a resistor.

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2002\01\16@120338 by Rudy Rudy

Set them as outputs.

-----------------------
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> {Original Message removed}

2002\01\16@151706 by Andre Abelian

two ways can be done.

1. make unused pins inputs and ground them.
2. make unused pins output and do not connect to any where
  do not ground output pins.


Andre Abelian




I will have several unused pins on my 16F877

Should the unused pins be set as inputs or outputs and should they be
tied
directly to GND or do I use a resistor.

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2002\01\16@154505 by iklas Wennerstrand

If you ground the input pin then you have to be seartain that you never ever
get a high value on that port pin.
That is if the MCU gets crazy and accidentelly shift to output and drive the
port pin high.
Bad to connect direct to ground without a current limiting resistor.
To lower cost and board space I would suggest alternative 2
Niklas

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För Andre Abelian
Skickat:        den 16 januari 2002 21:15
Till:   PICLISTSTOPspamMITVMA.MIT.EDU
Ämne: Re: [PIC]:What is the correct way to terminate unused pins 16F877

two ways can be done.

1. make unused pins inputs and ground them.
2. make unused pins output and do not connect to any where
  do not ground output pins.


Andre Abelian




I will have several unused pins on my 16F877

Should the unused pins be set as inputs or outputs and should they be
tied
directly to GND or do I use a resistor.

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'[PIC]: What to do with unused I/O pins'
2002\01\21@153712 by andyf

I am currently working on a gadget with a 12C508.  Three I/O pins (GP0, GP1 and GP4) are set as outputs and are used to provide a 'clock pulse' to some other circuitry.

When used in the field, any or all of these pins could be used, but probably only two at a time.

Should anything be done with these pins that aren't used?  They will be 'running' all the time, whether the signal is used or not.  Perhaps tie them to ground through a 10K resistor?  Or maybe they're fine left open?

What about unused I/O pins that aren't referenced in the program?  Should anything be done with them?  I'm basically trying to limit long term damage (re: my post about the life expentancy of a PIC).

Thanks for any input!

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2002\01\21@175454 by kben

Hi Andy
Try these from the PIC FAQ. ( I usually just set them as outputs)

www.piclist.com/techref/piclist/begin.htm
No. 9 from the list
Don't Float: Tie the switch pin Hi or Lo with a ~10K resistor or use internal
pullups to avoid floating inputs when the switch is open. In general, do something
with unused pins don't just leave them floating
also
http://www.piclist.com/techref/logic/xtrapins.htm

>I am currently working on a gadget with a 12C508.  Three I/O pins (GP0, GP1
and GP4) are set as outputs and are used to provide a 'clock pulse' to some
other circuitry.
>
>When used in the field, any or all of these pins could be used, but probably
only two at a time.
>
>Should anything be done with these pins that aren't used?  They will be 'running'
all the time, whether the signal is used or not.  Perhaps tie them to ground
through a 10K resistor?  Or maybe they're fine left open?
>
>What about unused I/O pins that aren't referenced in the program?  Should anything
be done with them?  I'm basically trying to limit long term damage (re: my post
about the life expentancy of a PIC).
>
>Thanks for any input!

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What should I do with the unused pins on a dual CMOS op-amp (specifically,
the National LM6482 rail-to-rail op amp)? If anything, is it enough to tie
the inputs of the unused op amp together? Should they also be grounded?

The datasheet had no recommendations, nor did the FAQ.

TIA,

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2002\03\01@195724 by Dave Dilatush

Rick Mann wrote...

>What should I do with the unused pins on a dual CMOS op-amp (specifically,
>the National LM6482 rail-to-rail op amp)? If anything, is it enough to tie
>the inputs of the unused op amp together? Should they also be grounded?
>
>The datasheet had no recommendations, nor did the FAQ.

You can tie one opamp input (doesn't matter which one) to one supply
rail, and the other opamp input to the other rail, and leave the output
open; or you can tie the output to the inverting input to make a
unity-gain follower, and then tie the non-inverting input to ground or
to either of the rails.

Either way, the output of the opamp is determinate and stable- which is
what you want so the unused opamp doesn't interfere with anything.

HTH...

Dave

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2002\03\01@210512 by Spehro Pefhany

At 04:38 PM 3/1/02 -0800, you wrote:
>What should I do with the unused pins on a dual CMOS op-amp (specifically,
>the National LM6482 rail-to-rail op amp)? If anything, is it enough to tie
>the inputs of the unused op amp together? Should they also be grounded?

The best thing to do in general is to connect the op-amp as a voltage-
follower (output to inverting input) and connect the non-inverting input to
ground if you have +/- supplies, or a voltage that the output can follow
to if you have a single supply. Next best thing is to ground the non-inverting
input with a single supply, and have output connected to inverting input.

Some op-amps do strange things when you go outside the common-mode range or
apply a high differential voltage. They can draw excessive input current
(Bipolar types sometimes have the equivalent of back-to-back diodes across
the input) or they can draw excessive supply current. Unfortunately they
often don't publish the schematics of the op-amps any more, so it's hard
to tell without actually testing. This one is a CMOS one, so it's immune to
some of the ills that affect bipolar rail-to-rail op-amps, but if you follow
the above ideas, you'll have more flexibility in dropping in alternative
op-amps if required.

Best regards,

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'[EE]: Unused pins on a comparator'
2002\03\03@123042 by Brian Kraut

This reminds me of something I came accross recently on an LM339
comparator.  I have a book that says to ground all unused pins of the
comparator.  I would think that with both input pins grounded that the
output would be unstable.  It seems to make more sense to me to ground
one input and connect the output to VCC to get a stable output.  Anyone
not agree?

Dave Dilatush wrote:

{Quote hidden}

>Rick Mann wrote...
>
>>What should I do with the unused pins on a dual CMOS op-amp (specifically,
>>the National LM6482 rail-to-rail op amp)? If anything, is it enough to tie
>>the inputs of the unused op amp together? Should they also be grounded?
>>
>>The datasheet had no recommendations, nor did the FAQ.
>>
>
>You can tie one opamp input (doesn't matter which one) to one supply
>rail, and the other opamp input to the other rail, and leave the output
>open; or you can tie the output to the inverting input to make a
>unity-gain follower, and then tie the non-inverting input to ground or
>to either of the rails.
>
>Either way, the output of the opamp is determinate and stable- which is
>what you want so the unused opamp doesn't interfere with anything.
>
>HTH...
>
>Dave
>
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2002\03\03@124505 by Spehro Pefhany

At 12:34 PM 3/2/02 -0800, you wrote:
>This reminds me of something I came accross recently on an LM339
>comparator.  I have a book that says to ground all unused pins of the
>comparator.  I would think that with both input pins grounded that the
>output would be unstable.  It seems to make more sense to me to ground
>one input and connect the output to VCC to get a stable output.  Anyone
>not agree?

I'd suggest following the original manufacturer's data-sheet
recommendation, which is to ground all 3 pins of unused comparators
(that includes the output).

(In unusual circumstances, there may be some benefit in low-level
reduced noise or current consumption with biasing it one way or the
other, but I'd prefer to see ~100mV to do it, not Vcc).

Connecting an open-collector output to Vcc is not a very good idea, but
you probably didn't actually mean to write that!

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
@spam@speffspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
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2002\03\03@124507 by Dave Dilatush

2002\03\03@125543 by Brian Kraut

2002\03\03@132524 by Dave Dilatush

2002\03\03@132731 by Spehro Pefhany

At 05:43 PM 3/3/02 +0000, you wrote:

>For the LM339, connecting one input to ground and the other input to VCC
>would be pointless because the LM339's input common-mode range does not
>include VCC; and when either of the inputs is outside the input CMR, the
>output is indeterminate.

Hmmm.. "indeterminate" or "unspecified"?  ;-)

From the internal schematic, it looks like tying both pins
to a voltage >> Vcc (but < 36V) will lead to a predictable result
(output low and and some  current saving). There's a range
around Vcc where the current sources are shutting down that won't be
so predictable if both inputs are in that same range, but if one pin
is within the common-mode range, the results from the other pin being
-0.3 < Vin < 36V should not be different from what you'd expect,
regardless of supply voltage.

(BTW, their assumption that ground = negative supply was corrected on
later data sheets, I guess some people didn't realize the reasoning)

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
TakeThisOuTspeffKILLspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
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2002\03\03@132944 by Brian Kraut

2002\03\03@133531 by Olin Lathrop

> This reminds me of something I came accross recently on an LM339
> comparator.  I have a book that says to ground all unused pins of the
> comparator.  I would think that with both input pins grounded that the
> output would be unstable.  It seems to make more sense to me to ground
> one input and connect the output to VCC to get a stable output.  Anyone
> not agree?

I don't like tying both input pins together because, as you say, it could be
unstable.  You are counting on the offset voltage to drive the output one
way.

However, I would definitely NOT tie one to power and the other to ground.
Depending on the input stage, that could draw excessive current or even
destroy the chip.  This is less likely to be a problem on comparators
because these are usually designed for a large differential mode input.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, .....olinRemoveMEembedinc.com, http://www.embedinc.com

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'[PIC]: filling unused program memory'
2002\03\12@180835 by Terence Monteith

I would like to fill in unused portions of the program memory with a
specific value (0x0000), but am unsure how this can be done without
tediously inserting the values manually or by using FILL directives
throughout the code.  Using a FILL directive at the very beginning of code
of course will give me overwrite errors when compiled.  Any suggestions?

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2002\03\12@183205 by mike

On Tue, 12 Mar 2002 16:55:29 -0600, you wrote:

>I would like to fill in unused portions of the program memory with a
>specific value (0x0000), why?

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2002\03\12@190027 by Pendley, Michael

2002\03\12@192431 by Sean Alcorn - Avion Sydney

on 13/3/02 10:31 AM, Mike Harrison at RemoveMEmikespamSTOPspamWHITEWING.CO.UK wrote:


>> I would like to fill in unused portions of the program memory with a
>> specific value (0x0000),
> why?

Probably because many text books have told him that he should.

That should spark a debate! :-)

Sean

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2002\03\13@100056 by Terence Monteith

2002\03\13@102520 by Claudio Tagliola

2002\03\13@102744 by Terence Monteith

No, then I get overwrite errors.

-----Original Message-----
From: Claudio Tagliola [spamBeGonecptagliolaRemoveMECHELLO.NL]
Sent: March 13, 2002 9:23 AM
To: .....PICLISTEraseMEMITVMA.MIT.EDU
Subject: Re: [PIC]: filling unused program memory


Can't you FILL the complete range as the first MPASM operator, and then
ORG back to the beginning?

-----Original Message-----
From: pic microcontroller discussion list
[spamPICLISTspam_OUT@spam@MITVMA.MIT.EDU] On Behalf Of Terence Monteith
Sent: woensdag 13 maart 2002 15:57
To: spamPICLIST@spam@STOPspamMITVMA.MIT.EDU
Subject: Re: [PIC]: filling unused program memory


Yes, I had thought of the FILL directive, but due to the nature of the
code (tables, code spread over 4 pages) I would need to put in quite a
few.  I was wondering if their was a more elegant way of doing this
using MPASM.

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2002\03\13@102951 by Carlos Ojea

2002\03\13@103749 by Pic Dude

Isn't this the purpose of erasing a chip before programming?  I'm new to
this PIC stuff still, but the Tait programmer I'm using seems to state
that using the erase command on the same command-line as dumping
the hex file to the PIC will erase the chip first and then drop on the
code whereever there is code.  All mem locations w/o code will not
be touched.

Cheers.


----- Original Message -----
From: "Terence Monteith" <spamBeGoneTerence.MonteithspamBeGone@spam@WAVECOM.CA>
To: <RemoveMEPICLISTRemoveMERemoveMEMITVMA.MIT.EDU>
Sent: Wednesday, March 13, 2002 9:25 AM
Subject: Re: [PIC]: filling unused program memory


> No, then I get overwrite errors.
>
> {Original Message removed}

2002\03\13@104238 by Terence Monteith

2002\03\13@104440 by Claudio Tagliola

2002\03\13@105535 by Terence Monteith

2002\03\13@130836 by Olin Lathrop

> Yes, I had thought of the FILL directive, but due to the nature of the
code
> (tables, code spread over 4 pages) I would need to put in quite a few.  I
> was wondering if their was a more elegant way of doing this using MPASM.

You could just post process the HEX file by inserting hard zeros for all
values that aren't explicitly specified.

> I am implementing code to reprogram the microcontroller remotely, and I
want
> to generate a hex file that will set all unused program words to 0x0000.
> This way I can determine if the code was loaded in the field (since the
> unused portions contain 0x0000), or if it was loaded at the factory (where
> unused portions will contain 0x3FFF).

How about a single ID or version word at a know location, like the last
location in memory.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olinKILLspamspamembedinc.com, http://www.embedinc.com

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2002\03\13@130847 by Olin Lathrop