  We have observed PSR~B1534+12 (J1537+1155), a pulsar with a neutron star
companion, using the Five-hundred-meter Aperture Spherical radio Telescope
(FAST). We found that this pulsar shows two distinct emission states: a weak
state with a wide pulse profile and a burst state with a narrow pulse profile.
The weak state is always present. We cannot, with our current data, determine
whether the pulse energy of the weak state follows a normal or a log-normal
distribution. The burst state energy distribution follows a power-law. The
amplitude of the single pulse emission in the burst state varies significantly;
the peak flux intensity of the brightest pulse is 334 times stronger than that
of the average pulse. We also examined the timing precision achievable using
only bright pulses, which showed no demonstrable improvement because of pulse
jitter and therefore quantified the jitter noise level for this pulsar.
