At 09:54 AM 7/11/02 -0700, John Dammeyer wrote:
>Hi guys,
>
>I've been looking at various PIC projects that are published out on the
>WEB and I find there is a major inconsistency with the reset circuits.
>Some folks use reset chips and others just tie the MCLR to Vcc through a
>resistor.  Given that the MCLR/VPP gets the 13V programming voltage are
>there special reset chips that will handle that?  Is there even a need
>with the PIC to have a reset chip?

I *always* have some form of reset circuit in my products - usually a
combination of time and supply voltage operated.  I'm told that the higher
end PICs don't require external reset anymore but, so far, projects that
use higher end PICs require some form of fail-safe and/or eeprom and I wind
up adding an external watchdog/supervisor/reset controller/eeprom chip
anyways.  Simple PICs (12c508) absolutely require a proper reset circuit if
they are fed from a mains supply and you are shipping thousands of them all
over the world.

I don't do ICSP with the small PICs - the code does not change often enough
to justify it.  They get batch programmed before they are installed on the
PCB.  I therefore don't have to worry about protecting components connected
to MCLR.

Projects using an external watchdog can be programmed through the watchdog
chip's socket.  The watchdog I use is the Xicor X5043: 512 bytes of eeprom,
watchdog, reset controller, power supply supervisor.  I use RB6,7 to talk
to the Xicor chip (and all the shift registers on the card), MCLR is tied
to one pin of that chip.  It is socketed: I just plug the ICSP cable into
that socket.

dwayne

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

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