On Thu, 2004-12-16 at 21:01 -0800, Bob Blick wrote:
> On 16 Dec 2004 at 22:40, Matt Pobursky wrote:
> > What I've done in the past is buffer the CLKOUT pin of the PIC with 
> > crystal using a "microgate" part like a TI SN74AHC1G14 Schmitt inverter
> > then connect to the other PIC's CLOCKIN pin. Set the second PIC config 
> > for EC mode. The advantage is you get very little loading on the PIC 
> > oscillator circuit (only adds a couple pF) and allows you to run the 
> > signal a much longer distance. The Schmitt gate also gives you a nice
> > clean clock that will be very close to 50% duty cycle.
> 
> This is what I really don't want. It will increase the radiated EMI 
> and make my power supply dirtier.
> 
> The first pic is plenty capable of driving the second pic, I want to 
> add the resistor to keep EMI as low as possible but not make the 
> resistor so large that it isn't reliable. 

Which will probably work on the bench, but fail at 5 degrees lower in
temp, or when the humidity rises, or when the PCB it's built on has
slightly thinner copper, etc. I personally see such an approach as
ASKING for gremlins.

If you are that concerned about EMI I'd go for some shielding. Better to
have a little shielding and a working circuit then a circuit that only
works when it feels like working IMHO. TTYL

-----------------------------
Herbert's PIC Stuff:
http://repatch.dyndns.org:8383/pic_stuff/

_______________________________________________
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist