> At 12:10 PM 6/1/01 -0500, Dale Botkin wrote:
> >Hi all,
> >
> >Last night I spent several hours wondering why a new project wouldn't work
> >most of the time. I was using a 12CE674-JW part, and could NOT get it to
> >run reliably -- maybe one in 20 tries it would start. I was using
> >internal RC osc, no CLR, power-up timer, with or without watchdog (didn't
> >seem to matter). I finally stripped it down to a blink-the-LED stage,
> >still didn't work. So I tried it with XT, 4MHz xtal, MCLR tied high. It
> >worked, but only after I momentarily grounded MCLR.
>
> Check your power supply. Try this: do the LED flash thingy but make it
> active LO. Connect the anode of the LED directly to the 5V supply,
> resistor from LED to PIC pin. Use a 100R resistor in series with the VDD
> pin on the PIC, with a 100n cap from VDD to VSS. Set all the other pins as
> outputs and let them float.
>
> Configure the PIC for internal RC, internal MCLR. Apply power, see if it
> works. If it fails, ground the VDD pin on the PIC momentarily and see if
> it works then. Note: the 100R resistor limits the short circuit current.
>
> I suspect you have one (or both) of two problems: rise time on VDD must be
> monotonic and fairly fast (<10 msec from 0V to VDD) *and* VDD must be less
> than 0.2Vdc when power is removed. You WILL have problems if you allow VDD
> to hover around 0.6 - 0.7 Vdc when power is turned off.
>
> I have found that I have to pay strict attention to what kind of power
> supply I feed the PIC with. I have tried many approaches, ranging from a
> simple 'hold the PIC in reset until after power is stable' (works every
> time but you lose MCLR) to fairly simple 'remove power from the PIC until
> the PSU is stable' type circuits (also works every time but costs parts).
>
> I probably should gather all my approaches onto a single schematic and post
> it somewhere. Lack of time right now, though.
>
> dwayne
>
>
>
>
> Dwayne Reid <
.....dwaynerKILLspam
.....planet.eon.net>
> Trinity Electronics Systems Ltd Edmonton, AB, CANADA
> (780) 489-3199 voice (780) 487-6397 fax
>
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