Immediate-release trazodone tablets release their full dose promptly and are typically taken multiple times a day for depression, or once at bedtime for off-label sleep use. An extended-release formulation (branded Oleptro) was designed for smoother, once-daily dosing with fewer peaks and troughs in blood level.
Today, the overwhelming majority of trazodone prescribed in the U.S. is the immediate-release generic tablet. If you're prescribed an extended-release product, it should generally not be split or crushed, since doing so can release the full dose at once rather than gradually.