Bob Blick wrote:

> Second question, does LP mode limit the crystal drive so a series resistor
> is not needed?

Hi Bob,

A single resistor, in some cases (like with tuning fork crystals), can
indeed be very cheap insurance against overdriving the crystal. Typically,
you see much lower maximum drive levels with tuning fork crystals, than with
non-tuning fork crystals.

Who's the manufacturer of the crystal you are using? I would always look at
the manufacturer's specifications for guidance on the maximum drive level
for the particular crystal you are working with. Some of the crystal
manufacturers even have application notes that show you how to measure the
drive level in situ. Even Microchip has a few application notes on
crystals -- I'm not sure if you have looked at these.

For example, a Fox Electronics HC49S crystal (3.200 ~ 70.000 MHz) has a
maximum drive level of 0.5 mW, and their FSN SMD tuning fork crystal (32.768
KHz) has a drive level of 1.0 uW: a drive level that is 500 times less.

Best regards,

Ken Pergola

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body