I am designing a product that generates some precisely timed signals.  I am
using a PIC16C84-4 with a 4Mhz XTAL.  Testing the code in mpsim shows that
my timing meets the spec. (min 55 usec max 61 usec 58 usec nominal)  MPSIM
shows my timing to be 57 usec and 59 usec using a 1 usec clock cycle (4 Mhz).
Analysis shows that +- 3% tolerance will work.  This should be no problem for
a XTAL right?  Well I put the device on the scope and my actual numbers were
min 60.6 usec max 62.2 usec.  This is about +- 5% and puts me out of spec.  I
could lower my time in software (short term fix) but this will make the design
difficult to produce.  I also have lots of stuff to do during the time between
transitions and lowering the time will impact my time line.  Any ideas on how
to adjust the frequency or why it would be 5% low?  I am using 30pf cap for
C1 and C2 of the crystal and am running the PIC in XT XTAL  mode.  I do not
have the resistor between the XTAL and OSC2 pin. (Ref data book p2-758)  The
XTAL is one from a local surplus shop but I have never had problems with their
crystals before.

Thanks for any help

Norm