# Pic Microcontroller - Secondary Oscillator

I am planning on using a 32.768KHz crystal as a real-time clock and connecting this to a pic microcontroller via the SOSCI and SOSCO The Crystal is a Seiko SSP‑T6 32.768KHz watch crystal in 8 × 2.1 × 1.6mm surface‑mount package. 20ppm accuracy. 7pF load capacitance. 55KΩ series resistance.

Now The datasheet recommends the following setup with a resistor R of 100K (see image below):

On the Internet I have seen designs whereby the resistor value is in the Mega Ohms range. Can anyone answer the following questions:
A) Whether a watch crystal is appropriate in this design.
B) What the purpose of R is here and whether a value of 100K is recommended as opposed to say using a 20M Ohm resistor?
C) What would happen if the resistor was left out as is the case for higher value crystals?

• @Peter - That resistor is for DC feedback, which biases the input DC level. A value of 1 to a few M$\Omega$ is typical for CMOS oscillators, for TTL it has to be much lower (a few k\\$\Omega). – stevenvh Aug 16 '12 at 12:13