Searching \ for '?? Short ??' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=short
Search entire site for: '?? Short ??'.

Truncated match.
PICList Thread
'?? Short ??'
2000\05\07@193810 by John Orhan

flavicon
face
Hi PICster's,
I have had a harrowing experience yesterday with a couple of old PIC16C55s.
I hope someone has an explanation of sorts (more for my own peace of mind)
for what I will convey. I was trying to program the '55 with standard
header,etc to do the LED-flash trick (before starting the main program) and
found upon power-up that the device was drawing almost 1A! Power supply
checked out, put the chip back in - same thing. I even tried another '55
chip with the same results. Has anyone heard of these devices shorting?
There are no tricks with what I'm doing....chip control ( reset, etc) logic
levels are in their right states. Please advise.

John Orhan
Detection Systems / EDM Engineering Department
Ph: 02 96721233 (ext 219)
Fx: 02 9672 4093
Email: spam_OUTjorhanTakeThisOuTspamedm.com.au

2000\05\07@194844 by Tony Nixon

flavicon
picon face
John Orhan wrote:
>
> Hi PICster's,
> I have had a harrowing experience yesterday with a couple of old PIC16C55s.
> I hope someone has an explanation of sorts (more for my own peace of mind)
> for what I will convey. I was trying to program the '55 with standard
> header,etc to do the LED-flash trick (before starting the main program) and
> found upon power-up that the device was drawing almost 1A! Power supply
> checked out, put the chip back in - same thing. I even tried another '55
> chip with the same results. Has anyone heard of these devices shorting?
> There are no tricks with what I'm doing....chip control ( reset, etc) logic
> levels are in their right states. Please advise.
>
> John Orhan
> Detection Systems / EDM Engineering Department
> Ph: 02 96721233 (ext 219)
> Fx: 02 9672 4093
> Email: .....jorhanKILLspamspam@spam@edm.com.au

Are the IO pins set as outputs and hard connected to 5V or GND?
Is the chip in backwards?
Tie MCLR low instead of high and see if the short still exists.
Maybe they are duds.

--
Best regards

Tony

http://www.picnpoke.com
salesspamKILLspampicnpoke.com

2000\05\07@200542 by John Orhan

flavicon
face
Hi Tony and thanks for your resopnse,
I/O that is not used is floating, only porta is configured as an output port
to toggle A0 on and off. The fault exists in reset state. Any ideas? I guess
I would throw them out if I was sure that I had done everything correctly
and they still did'nt work. Chip is in the right way ( I made sure of that
one from the start). Please advise.

                                       John

{Original Message removed}

2000\05\07@201219 by Sean Breheny

face picon face
Hi John,

Did you check the circuit without the chip in?

Also, you might try taking a conductivity tester and checking the chip
itself to see if it is internally shorted.

Sean

At 10:04 AM 5/8/00 +1000, you wrote:
>Hi Tony and thanks for your resopnse,
>I/O that is not used is floating, only porta is configured as an output port
>to toggle A0 on and off. The fault exists in reset state. Any ideas? I guess
>I would throw them out if I was sure that I had done everything correctly
>and they still did'nt work. Chip is in the right way ( I made sure of that
>one from the start). Please advise.
>
>                                        John
>
>{Original Message removed}

2000\05\07@202039 by Tony Nixon

flavicon
picon face
John Orhan wrote:
>
> Hi Tony and thanks for your resopnse,
> I/O that is not used is floating, only porta is configured as an output port
> to toggle A0 on and off. The fault exists in reset state. Any ideas? I guess
> I would throw them out if I was sure that I had done everything correctly
> and they still did'nt work. Chip is in the right way ( I made sure of that
> one from the start). Please advise.

I would've make all unused pins outputs and make sure they are not
connected to anything. Floating inputs cause problems.

If the fault exists only when the chip is inserted, check that 5 VOLTS
is on pin 2 and GND is on pin 4. Make sure no voltage is connected to
OSC2.

If this checks out and the chips are inserted correctly, I would assume
they are faulty.

Did they program and verify OK?

--
Best regards

Tony

http://www.picnpoke.com
.....salesKILLspamspam.....picnpoke.com

2000\05\07@202046 by David Duffy

flavicon
face
<x-flowed>Hi John,
I had a dud batch of 16C57's quite a while ago - drew lots of current.
The distributor at the time replaced them & no problems after that.
Make sure any unused i/o is either programmed as output or tied hi/low.

At 09:37 5/8/00 +1000, you wrote:
{Quote hidden}

</x-flowed>

2000\05\07@203531 by John Orhan

flavicon
face
Hi Sean,
Yes. Checked everything like that - its in the right way, all I/O accounted
for but un-used, correct control, logic,etc

{Original Message removed}

2000\05\07@203742 by John Orhan

flavicon
face
Hi Tony,
All I/O is accounted for and power supply is OK, nothing going into OCS2 but
XTAL. They both programmed and veryfied OK.

{Original Message removed}

2000\05\07@203954 by John Orhan

flavicon
face
Hi David,
I will try that out . Many thanks for your reply.

-----Original Message-----
From: David Duffy [piclistspamspam_OUTAUDIOVISUALDEVICES.COM.AU]
Sent: Monday, 8 May 2000 10:18
To: @spam@PICLISTKILLspamspamMITVMA.MIT.EDU
Subject: Re: ?? Short ??


Hi John,
I had a dud batch of 16C57's quite a while ago - drew lots of current.
The distributor at the time replaced them & no problems after that.
Make sure any unused i/o is either programmed as output or tied hi/low.

At 09:37 5/8/00 +1000, you wrote:
{Quote hidden}

2000\05\07@204817 by Sean Breheny

face picon face
John,

I don't understand. They program OK but draw tons of current when you put
them in a normal circuit, regardless of whether or not they are in reset?
If they program OK, it can't be a simple short of power/GND since they
require power and GND to program, do they not? (Never have used the the
16C55 or 57)

Sean

At 10:36 AM 5/8/00 +1000, you wrote:
>Hi Tony,
>All I/O is accounted for and power supply is OK, nothing going into OCS2 but
>XTAL. They both programmed and veryfied OK.
>
>{Original Message removed}

2000\05\07@210103 by l.allen

picon face
John wrote

> Hi Tony,
> All I/O is accounted for and power supply is OK, nothing going into OCS2 but
> XTAL. They both programmed and veryfied OK.
>
I would reiterate the afore mentioned posts, it is very
likely the power supply on the target is reversed OR you
have a major common (zerovolts) mismatch between
parts of the project.

Note: (I am trying to help not be a swine) but VDD is +ve
and VSS is 0volts. I have seen people get this mixed up.




_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

2000\05\07@210737 by Tony Nixon

flavicon
picon face
Sean Breheny wrote:
>
> John,
>
> I don't understand. They program OK but draw tons of current when you put
> them in a normal circuit, regardless of whether or not they are in reset?
> If they program OK, it can't be a simple short of power/GND since they
> require power and GND to program, do they not? (Never have used the the
> 16C55 or 57)

You didn't get confused with the PDIP and SSOP pinouts in the data
sheet.

--
Best regards

Tony

http://www.picnpoke.com
RemoveMEsalesTakeThisOuTspampicnpoke.com

2000\05\07@211520 by John Orhan

flavicon
face
Hi Tony,
No. These are DIP devices and to avoid that very problem I cicle the one I'm
using at the time as that has happened in the past.

{Original Message removed}

2000\05\07@212148 by John Orhan

flavicon
face
Hi Sean,
Yes its got me too. I havn't used these devices either and was only
using-them-up in this simple application as I had a couple laying around
with a '57 as well. At this point nothing but clock,reset, 5v and ground are
connected to this device. The XTAL has worked elsewhere and the same PCB is
now powering a PIC16C84 that is working fine. I just don't know what it is
and have spent conciderable hours looking at this problem. It may well be
just some lines in the initialization of the device, but then I wiould have
expected MPLAB to pick up the fatal ones. Ideas?

{Original Message removed}

2000\05\07@221246 by Spehro Pefhany

picon face
At 09:37 AM 5/8/00 +1000, you wrote:
>Hi PICster's,
>I have had a harrowing experience yesterday with a couple of old PIC16C55s.

Ok, it sounds as if you have experienced what is called "latch-up".

All CMOS chips will do this, PIC's are relatively immune, but what happens
is this..

Somehow the protection diodes on at least one input get forward biased, that
means that the voltage must be a bit above Vdd or a bit below Vss (by a
diode drop).  Fine, they are designed to work this way, if , *however* the
current has for even a microsecond exceeded the maximum (in the low 10's
of mA) then latch-up occurs.

Essentially there is a parasitic SCR present in all these chips between Vss
and
Vdd, just waiting for a gate signal. When it turns on, you get about 1V from
Vss to Vdd, even at 100's of mA. Like all SCR's it will stay on until the
current from Vdd to Vss drops below the holding current of a few 10's of mA
(like when you notice it is getting hot and cut the power).

If the power supply is current limited, the chip may even survive this nasty
experience, though high temperatures may damage or degrade it.

It is often caused by applying a signal to an input without any series
impedance before power is applied to the chip, or by static discharge into
an unprotected input.

Hope this helps,

Best regards,
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spamBeGonespeffspamBeGonespaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

2000\05\07@222950 by John Orhan

flavicon
face
Hi Spehro,
And thanks for your reply. I have a 7805 reg in there thats good for about
an amp. It shares the common ground and positive 5V with the '55. The
control lines are accounted for at either 0V or 5V. The chip would probably
get hot as if I let it go for longer than 2 - 3 seconds. For latch-up to
occur, would I not need a bias from somewhere? Apart from porta and control
lines, everything else is floating. I don't quite understand.

{Original Message removed}

2000\05\07@223606 by Spehro Pefhany
picon face
At 12:28 PM 5/8/00 +1000, you wrote:
>Hi Spehro,
>And thanks for your reply. I have a 7805 reg in there thats good for about
>an amp. It shares the common ground and positive 5V with the '55. The
>control lines are accounted for at either 0V or 5V. The chip would probably
>get hot as if I let it go for longer than 2 - 3 seconds. For latch-up to
>occur, would I not need a bias from somewhere? Apart from porta and control
>lines, everything else is floating. I don't quite understand.

I've seen it happen with a multimeter test probe (when it is first
connected).

I've also seen it with power supply connection problems (like a missing
ground wire).

Could be something else, of course, but it sounds like the classic symptoms.

Best regards,



=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Spehro Pefhany --"it's the network..."            "The Journey is the reward"
TakeThisOuTspeffEraseMEspamspam_OUTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

2000\05\08@001528 by John Orhan

flavicon
face
Hi,
I definately am not missing a ground. The power supply has correct polarity
and voltage. Definatley checked out many times. There are only four grounds
and two 5v connections. If it is latch, up under those conditions would it
not also latch-up the 'c84 thats in there now? I'm only loading it with a
CRO and logic probe which have input impedance of several hundred k. Would
it be safe to say they're throw-away items?

{Original Message removed}

2000\05\08@003013 by Sean Breheny

face picon face
John,

Something must be going on here and I think you should try to figure out
what it is(even more carefully than you have) before you throw out the
parts. The reason I say this is that you say that you can program the
device just fine, but if you place it in this other circuit in reset, it
draws a huge amount of current. This would imply (assuming that your
circuit is acting as expected) that the only thing which causes the chip to
switch between acting normally and drawing a huge current is the presence
of the programming lines (and possibly programming voltage).

Here's what I would suggest: take a solderless breadboard and build a new
circuit which JUST has a 5V regulator(even better, a known good 5V power
supply), a capacitor to bypass the Vdd line(as an added protection against
regulator instability) and the 16C55. Attach power, gnd, and MCLR to GND.
See if it misbehaves. If yes, it's probably something REALLY weird with the
chip. If not, then there is something going on with your original circuit.
Where are you measuring the large current? Before or after the regulator?
Could it be that the regulator is going into oscillations under certain
circumstances?

You could also try scoping the power on your original circuit to see if it
is good and stable at 5V.

Sean

At 02:14 PM 5/8/00 +1000, you wrote:
>Hi,
>I definately am not missing a ground. The power supply has correct polarity
>and voltage. Definatley checked out many times. There are only four grounds
>and two 5v connections. If it is latch, up under those conditions would it
>not also latch-up the 'c84 thats in there now? I'm only loading it with a
>CRO and logic probe which have input impedance of several hundred k. Would
>it be safe to say they're throw-away items?
>
>{Original Message removed}

2000\05\08@005332 by John Orhan

flavicon
face
Hi Sean,
Thanks for your tip. Current was measured as total ( sum)from the bench-top
power supply. I had taken into account the charging of the caps ( aruond
470uF).I will give your idea a try. Thanks again.

                                       John

{Original Message removed}

2000\05\08@022742 by Tony Nixon

flavicon
picon face
John Orhan wrote:

> Apart from porta and control
> lines, everything else is floating. I don't quite understand.

Before proceding, I would change the TRIS regs to be all outputs.


--
Best regards

Tony

http://www.picnpoke.com
RemoveMEsalesspamTakeThisOuTpicnpoke.com

2000\05\08@023738 by David VanHorn

flavicon
face
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1


>Before proceding, I would change the TRIS regs to be all outputs.

A VERY good idea!  My stock template apps have all the I/O pins set to
outputs, and I convert them to inputs as I use them. One more buglet
pre-emptively squashed. :)

- --
Are you an ISP?  Tired of spam?
http://www.spamwhack.com  A pre-emptive strike against spam!

Where's Dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9

-----BEGIN PGP SIGNATURE-----
Version: PGPfreeware 6.5.2 for non-commercial use <http://www.pgp.com>

iQA/AwUBORZ6doFlGDz1l6VWEQKDPACfYkoL6fr1ncNw7s8Yw87H3hlws34AmwS5
2r/PjEftFN2yNdmZ2IbCU53x
=3DmX
-----END PGP SIGNATURE-----

2000\05\08@143139 by Alice Campbell

flavicon
face
try putting a (misc small signal) diode between MCLR switch
and the + rail to prevent voltage on mclr going up to the +
pic supply thru the switch.  My toasted pic rate went way
down after i started doing this.

alice

> Hi,
> I definately am not missing a ground. The power supply has correct polarity
> and voltage. Definatley checked out many times. There are only four grounds
> and two 5v connections. If it is latch, up under those conditions would it
> not also latch-up the 'c84 thats in there now? I'm only loading it with a
> CRO and logic probe which have input impedance of several hundred k. Would
> it be safe to say they're throw-away items?
>
> {Original Message removed}

2000\05\09@183719 by John Orhan

flavicon
face
Hi Alice,
Many thanks for your tip. I will give it a go and possibly avoid the loss of
the PICs.

                               John

{Original Message removed}

2000\05\09@190246 by Peter L. Peres

picon face
Hi,

I've been reading this thread and I have a gut feeling about it. I had a
PIC board where the MCLR trace went under the PIC and got shorted to +Vcc.
The board worked perfectly (I used the watchdog), but it would behave
strangely when the reset button fitted for testing was pressed - for
obvious reasons. In theory, it is enough if it is shorted to any pin that
is programmed as output and HIGH for this to happen.

Another thing to check is whether the ICSP parts relevant to MCLR are
fitted correctly, i.e. no 22 ohms instead of 22K reset pullup, Shottky
diode mounted the right way around and not shorted (by overheating when
soldering), etc.

2 bits,

       Peter

2000\05\09@194745 by John Orhan

flavicon
face
Hi Peter,
Thanks for your tip. I'll give it a go as well. Nothing to lose at this
point.

-----Original Message-----
From: Peter L. Peres [plpEraseMEspam.....ACTCOM.CO.IL]
Sent: Tuesday, 9 May 2000 3:01
To: EraseMEPICLISTspamMITVMA.MIT.EDU
Subject: Re: ?? Short ??


Hi,

I've been reading this thread and I have a gut feeling about it. I had a
PIC board where the MCLR trace went under the PIC and got shorted to +Vcc.
The board worked perfectly (I used the watchdog), but it would behave
strangely when the reset button fitted for testing was pressed - for
obvious reasons. In theory, it is enough if it is shorted to any pin that
is programmed as output and HIGH for this to happen.

Another thing to check is whether the ICSP parts relevant to MCLR are
fitted correctly, i.e. no 22 ohms instead of 22K reset pullup, Shottky
diode mounted the right way around and not shorted (by overheating when
soldering), etc.

2 bits,

       Peter

More... (looser matching)
- Last day of these posts
- In 2000 , 2001 only
- Today
- New search...