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PICList Thread
'Reset, repeate PLEASE!!'
1999\12\13@180155 by Giles L. Honeycutt

We are having a little trouble with our PICs.  I have included the
information that my co-worker sent to the C compiler listserv.  Anyway, I do
not know if it is hardware or software.  Basically I want to know how
repeatable a reset via touching the  reset line to GND is.  Any suggestions
on how to handle the resets is welcome.  I am about to dissect the ASM from
the C and verify all possibilities.

Information submitted to the C compiler listserv:
We are using the CCS PCM C Compiler, Version 2.693, 7652

I have been working with 16f876-20 rev B4 chips, and using a simple MCLR
10k resistor & 1uF cap (and diode to Vcc for power down).

I have 3 identical PIC's on this board they share common MCLR and
OSC lines (they go through 22 ohm for each PIC)

I observe the operation of the PIC's through 5 LEDs all on one port.

The problem is that when I short the MCLR pin to ground it doesn't reset
as I expect.  What it does do is:
Running normal
no LED's
Running normal
no LED's
???? no LED's

It is very repeatable for no LED's to follow Normal running, but
it is only 75% for Normal running to follow no LED's.

Also since I have enabled a #INT_RTCC and a #INT_SSP function, the
processors will occasionally completely lock up, with no recovery
unless the power is cycled.

I have #fuses HS,NOPROTECT, NOWDT, PUT, NOBROWNOUT and I have added

Does the compiler not identify reset during normal operation correctly?
Is this a silicon problem?
Is this my problem?

I don't want to mess with a WDT, but it looks as if I will have to, unless
can help...

1999\12\13@184607 by J Borgaard

May not be related, but I recently had similar behavior on a 16f84,
noticeable on power-up or reset. The problem turned out to be the failure to
clear a variable which was used to lookup values in a table of 16 items. I
did not limit the value of the variable before the lookup, and when the chip
was powered up, the variable was in an unknown state, sometimes of a value
greater than 16. This would cause execution to proceed beyond the lookup
table resulting in erratic operation and the occasional (apparent) halt. I
spent many hours on this and have learned the hard way to either set my
variables to a known state at the start and/or limit their range.

> {Original Message removed}

1999\12\14@020324 by Dr. Imre Bartfai


a question:

what do you mean exactly in the section below?

On Mon, 13 Dec 1999, Giles L. Honeycutt wrote:

--- snip ---
> I have 3 identical PIC's on this board they share common MCLR and
> OSC lines (they go through 22 ohm for each PIC)
--- snip ---

I would guess they OSC lines may not be wired simple parallel. If you did
so, it is a problem. I suggest set up ONE oscillator as normal, then tie
the remaining CHIP's CLKIN to the master's CLKOUT. And that is!

--- snip ---
> Does the compiler not identify reset during normal operation correctly?
--- snip ---

The question above does not make any sense as compiler does not have to
identify reset. MCLR Reset is an immediate hardware action.

On the other hand, similar problem can occur if MCLR are pulled up
incorrectly. Please measure voltage on MCLR pin at running system. It may
not be significantly less than Vdd.


1999\12\14@141701 by Andre Abelian

picon face
Since you have more then one pic connected together and you
do not know witch one is casing the problem or you do not even
know if it is pic related problem ( 99.9% not ) this is what you
need to do.

1. separate all 4 pics from each other separate MCR, and use crystals
   for each one or resonator. Use 39-100 pf cap on master clear pin with
10k pull-up
  and .1 mf on power VDD pin forget about using can oscillator for now
   your reset is going to be main power ( if you want to use it ) and  try
   every thing just you ware doing it before. If you couldn't duplicate
   the problem that means what ever you ware doing with can oscillator the
   problem is there. Do not forget that the crystal is analog if you
  are working with wire type of prototyping boards then you should
  use shielded cable for cans only unless they are very close to each
  Do not forget that the scope probe has at list 15pf cap in it
  when you are doing measurement  both caps should have same value
  your sine wave will be shifted or no clock at all. I personally use 2
same kind
  of probes and I connect them to both crystal pins unless you can buy a
  that do not have cap in it.

Andre Abelian

{Quote hidden}

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