  We present new X-ray timing and spectral observations of PSR J1930+1852, the
young energetic pulsar at the center of the non-thermal supernova remnant
G54.1+0.3. Using data obtained with the Rossi X-ray Timing Explorer and Chandra
X-ray observatories we have derived an updated timing ephemeris of the 136 ms
pulsar spanning 6 years. During this interval, however, the period evolution
shows significant variability from the best fit constant spin-down rate of
$\dot P = 7.5112(6) \times 10^{-13}$ s s$^{-1}$, suggesting strong timing noise
and/or glitch activity. The X-ray emission is highly pulsed ($71\pm5%$
modulation) and is characterized by an asymmetric, broad profile ($\sim 70%$
duty cycle) which is nearly twice the radio width. The spectrum of the pulsed
emission is well fitted with an absorbed power law of photon index $\Gamma =
1.2\pm0.2$; this is marginally harder than that of the unpulsed component. The
total 2-10 keV flux of the pulsar is $1.7 \times 10^{-12}$ erg cm$^{-2}$
s$^{-1}$. These results confirm PSR J1930+1852 as a typical Crab-like pulsar.
