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'[PIC]: PIC heating up'
2002\03\09@131238 by Code

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Hi,

   I built a circuit interfacing a MAX153 parallel 8 bit ADC and a MAX205
RS232 transceiver to a 16F628. It is supposed to read the parallel ADC
output and serialize the data before sending to the computer.

The PIC in this case is running very very hot, i could barely touch it for a
sec. What could be the cause?

this is the ASM its running.
main:    call init
loop:    movlw D'100'
           call  nmsec
           bsf PORTB,0
           call micro4
           bcf PORTB,0

           movf PORTA,0    ; PORTA reads lower 1/2 the byte
           addwf PORTB,0    ; PORTB 4-7 reads higher 1/2 and combines into
1 byte to W

           movwf  TXREG
           goto  loop

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2002\03\09@132426 by Dave Dilatush

picon face
Code wrote...

>RS232 transceiver to a 16F628. It is supposed to read the parallel ADC
>output and serialize the data before sending to the computer.
>
>The PIC in this case is running very very hot, i could barely touch it for a
>sec. What could be the cause?
>
>this is the ASM its running.

[assembly language code snipped]

Forget the code; your PIC isn't running any program if it's so hot it
burns your fingers.  These things normally run stone cold.

You've got something connected wrong; possible your power supply
polarity is reversed.  Go back and check your connections, CAREFULLY.

DD

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2002\03\09@141238 by Code

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It's now dead.

Before it died, the code ran as expected, albeit with the PIC running very
hot. Power Supply is of the correct polarity, 200Ohm resistor between MCLR
and VCC.

I disconnected every I/O port and it was still running hot, the case of
sinking or sourcing too much current can be disregarded.

What could be the caused?


{Original Message removed}

2002\03\09@141859 by Spehro Pefhany

picon face
At 06:22 PM 3/9/02 +0000, you wrote:

>Forget the code; your PIC isn't running any program if it's so hot it
>burns your fingers.  These things normally run stone cold.

Agree. Microchip never implemented Motorola's "HCF" instruction in PICs.
(Halt and Catch Fire)

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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2002\03\09@142110 by engelec

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Without knowing much about your design this is what I would do.

1. disconnect every thing that connected to the pic.
2. do you have a clock ? is 5v looks clean on the scope ?
  is it getting hot? If all of this is good then connect next
  possible chip that you can run it and check it again.
  Put your scope on AC and look for noise on 5v line or data line.
  It sounds like you have EMI or RFI problem. Did you fallow single
  Point ground rule? There are so many questions about this.


Andre Abelian







{Original Message removed}

2002\03\09@142522 by Code

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The ohmmeter reads 780Ohms between Vss and Vdd on the dead f628, a healthly
PIC has infinite resistance.
{Original Message removed}

2002\03\09@144021 by Dave Dilatush

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Spehro Pefhany wrote...

>At 06:22 PM 3/9/02 +0000, you wrote:
>
>>Forget the code; your PIC isn't running any program if it's so hot it
>>burns your fingers.  These things normally run stone cold.
>
>Agree. Microchip never implemented Motorola's "HCF" instruction in PICs.
>(Halt and Catch Fire)

Wow, I didn't know they had one, and I spent many years working with
MC6800's and MC68HC11's.

There were all sorts of unused opcodes on the original 6800; some did
screwy things.

I recall the 0x00 opcode caused the CPU to drop everything and begin
incrementing the program counter at clock speed, with the output
appearing on the address lines (some sort of test "feature", I suppose).


And there were perfectly legitimate instructions that would actually
execute without mishap, but made absolutely no logical sense--like the
STX Immediate opcode.

But a true-blue Halt And Catch Fire instruction?  Complete with smoke
and charred encapsulant?  Nifty... glad I never encountered it!

Cheers,

Dave

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2002\03\09@144352 by Spehro Pefhany

picon face
At 03:12 AM 3/10/02 +0800, you wrote:


>I disconnected every I/O port and it was still running hot, the case of
>sinking or sourcing too much current can be disregarded.
>
>What could be the caused?


Sounds like latch-up. A momentary voltage excursion at most any of the
pints (with a few exceptions) outside the Vdd-Vss range, that has more
than a few dozens of mA flowing, even for a microsecond, runs the
risk of latching up the chip. Then massive current flows from Vdd to
Vss inside the chip, because the parasitic SCR has been turned on.
If the supply current is limited, interrupting the Vdd supply momentarily
may save it. One common cause of this is having two power supplies
so that when the PIC is off the current flows into inputs from
elsewhere. Then it's primed to turn on when Vdd appears. Another
possibility is test leads and static electricity. Chips these days
are very resistant to latchup, it used to be about an order of
magnitude easier to cause. I have not seen it personally in many, many
years.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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2002\03\09@144810 by Dave Dilatush

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Code wrote...

>It's now dead.

I'm sorry to hear that.  That's sad.

>Before it died, the code ran as expected, albeit with the PIC running very
>hot. Power Supply is of the correct polarity, 200Ohm resistor between MCLR
>and VCC.

What's the power supply voltage?  It should be 5.0 volts, approximately;
if it's more than 6 volts, you've got troubles.

>I disconnected every I/O port and it was still running hot, the case of
>sinking or sourcing too much current can be disregarded.
>
>What could be the caused?

The possibilities are very limited:

1. Vcc is too high;

2. Vcc and ground are reversed;

3. Vcc is AC, not DC;

4. Something else is sourcing current into the PIC, causing latchup;

5. PIC plugged in wrong;

6. PIC wired wrong;

7. Pin numbers on PIC misinterpreted; or

8. PIC was dead to begin with.

That's just about the entire universe of possible causes.  Maybe I could
think of more if I had more coffee in me, but I think that's it.

It must be one of the above.

In any case, PICs simply do not run hot unless there is something
horribly, terribly wrong.  And in most cases, they don't even run
slightly warm.

Dave

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2002\03\09@170504 by Herbert Graf

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A PIC being so hot that you can't touch it has nothing to do with the code
inside, you have hooked something up incorrectly. Most likely you have
revesred the power hookups. Chances are though that the PIC has survived,
they are quite persistant little buggers when it comes to mistakes in
hookup. TTYL

> {Original Message removed}

2002\03\09@171919 by Dwayne Reid

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At 02:11 AM 3/10/02 +0800, Code wrote:
>Hi,
>
>     I built a circuit interfacing a MAX153 parallel 8 bit ADC and a MAX205
>RS232 transceiver to a 16F628. It is supposed to read the parallel ADC
>output and serialize the data before sending to the computer.
>
>The PIC in this case is running very very hot, i could barely touch it for a
>sec. What could be the cause?

I assume from your post that you are getting the expected results from your
code and that the only unusual thing is that the PIC is running hot.  All I
can think of in that case is an output pin that is being held hard to
ground or VDD.  Double check the pins you are using for VDD and GND - I
have seen a PIC still operate even when power was connected to a port pin
instead of the correct power pin on the package.

Try disconnecting all pins tied to GND & VDD except the power
pins.  Configure the '628 for internal MCLR.  See if the heat still
continues.  If it does, try programming another PIC and sticking it in the
same circuit.  Chances are the 1st PIC had a pin driver zapped and a new
PIC will fix the problem.

dwayne


Dwayne Reid   <dwaynerspamKILLspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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