>Referencing the PIC16/17 Microcontroller Data Book in the PIC16C84 section
>subsection 8.2.2 "The PIC16C84 oscillator design requires the use of a parallel
>cut crystal. Use of a series cut crystal may give a frequency out of
>the crystal manufactures specifications"

>Also referencing the PIC16C84 section table 8-2 crystals tested:
>ECS ECS-40-S-4

>Also referencing the Digikey July-August 1996 catalog page 179
>Frequency               4.000 Mhz
>Max Series Load Cap.    Series
>ECS Part No             ECS-40-S-4

>Could some one explain this to me?

Somebody goofed.

All crystals have two natural resonant frequencies.  When a crystal is modeled
as a circuit if inductors, capacitors, and resistors; there are two resonant
circuits, one is an LC series circuit and one is a parallel one.  A parallel
LC circuit has its maximum impedance at the resonant frequency where a series
resonant circuit has its minimum impedance at resonance.  Therefore, different
oscillator ciruit topology is required.
A "series resonant" crystal is intended for use as if it were the series
resonant circuit and, if operated in a parallel resonant oscillator like the
PIC, may oscillate at the parallel frequency (if at all) which is not the rated
frequency.

>Do I have to look for a Load Cap. rating of series to get a parallel cut
>crystal and not a series?

No.  You really want a parallel crystal with a load cap rating, usually around
20 pF.

- Mark Sullivan -