PICmicros instruction counter synchronization

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Does anyone know if any of the Microchip PICmicros reset their
divide-by-four instruction counter during a hardware reset?  I need to
drive an array of PICs from a single clock, and more than that, I need
all the PICs to be exactly synchronized with respect to their
instruction cycles.  I am hoping that releasing them from reset at the
same time will accomplish this goal.  I am looking primarily at the
low to mid range PICs.


-Robert Scott
 Ypsilanti, Michigan
(Reply through this forum, not by direct e-mail to me, as automatic reply
address is fake.)

Re: PICmicros instruction counter synchronization
On Thu, 26 Aug 2004 00:58:25 GMT, the renowned no-one@dont-mail-me.com

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Yes it is held in Q1 state during reset (midrange at least).  

I hope you're going to re-synchronize them from time to time..

Best regards,
Spehro Pefhany
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Re: PICmicros instruction counter synchronization
On Thu, 26 Aug 2004 01:39:23 GMT, Spehro Pefhany

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Ah... but upon release of reset (which may have slightly different analog
signals arriving internally), will all the parts come out of reset and execute
their first Q1 phase on exactly the same, precise external clock tick?

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With a circuit to skip any necessary clock pulses needed to re-align their Q1
phases with some primary CPU?

Jon

Re: PICmicros instruction counter synchronization
On Thu, 26 Aug 2004 04:57:34 GMT, the renowned Jonathan Kirwan

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Sure, provided the /RESET edge is properly synchronized with the
common external clock, so there are setup and hold times that are not
marginal. That's all under his control.

Best regards,
Spehro Pefhany
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Re: PICmicros instruction counter synchronization
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  Some uC have noise filters on the RESET lines. eg early AVRs were very
susceptable to this, and so newer ones have a 2.5us 'spike filter', plus
they also have additional coming-out-of-reset delays.
  ie you will need to test the specific PIC member, and might like to
include :-
  - Lower Freq clock around RESET, to tolerate RC delays
  - Some means to actually verify LOCK, probably via a Interrupt sync pulse
  A PLD could manage both tasks.


Re: PICmicros instruction counter synchronization
On Thu, 26 Aug 2004 17:29:06 +1200, the renowned Jim Granville

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The PWRT(imer) can be disabled on midrange PICs. THe OST(imer) is
automatically disabled when external clock is selected. If there is a
spike filter that could cause problems at high clock speeds.

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That's a possibility. The minimum reset width is spec'd at 2usec.

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Sure. Or maybe just a FF is required. I suspect if he had a PLD
available he might not be worrying about this particular issue.  

At higher clock speeds (maybe over 4MHz) those things and more will
probably come into play. The delay from the clock rising edge to a
port pin changing state is (on one particular chip) as much as 150nsec
(typical 50, with no minimum). At 20MHz, each Q state is only 50nsec,
so the possible unit-to-unit variation is more than one Q state.

Best regards,
Spehro Pefhany
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"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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