At 08:30 AM 2/22/00 -0800, you wrote:
> Regarding MCLR...If it were me, I'd put a pullup resistor of
> say 4.7K ohms from Vdd to MCLR, and a .1 uF cap from MCLR to
> Ground.  For a manual RESET switch, put a N.O. PB across the
> .1 uF cap.  So, when you first turn it on, the cap is
> discharged and represents a short which pulls reset low, and
> holds it there until the cap starts charging.
.......
>                                       Regards,
>                                        Jim

Jim,

I'd add a mod here. First, (.1uf)*(4700) only gives a .00047 sec
RC time constant, which may not hold the MCLR line low long enough
for reset. You need a much bigger cap, say 22 uF, which gives .1 sec
time constant. Don't increase R by too much, as leakage can be a
factor.

Secondly, I've found, much to my chagrin (meaning $$$ wasted),
that you don't want to tie a capacitor straight onto MCLR on a PIC,
as this can damage the chip and lead to very large leakage
currents into the MCLR line (order of 100s of uA). Use at least
100 ohms between the cap and MCLR.

More info about this particular problem is in the Piclinks
page *PIC ERRATA* section on my website -

http://www.sni.net/~oricom/piclinks.htm

- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom