Not sure of the Pspice syntax, but Hspice is
Vxxx n+ n- PU<LSE> <(>v1 v2 <td <tr <tf <pw <per>>>>> <)>
where:
Vxxx, Ixxx Independent voltage source which will exhibit the
pulse response.
PULSE Keyword for a pulsed time-varying source. The
short form is ‘PU’.
v1 Initial value of the voltage or current, before the
pulse onset (units of volts or amps).
v2 Pulse plateau value (units of volts or amps).
td Delay time in seconds from the beginning of
transient interval to the first onset ramp.
Default=0.0 and negative values are considered as
zero.
tr Duration of the onset ramp in seconds, from the
initial value to the pulse plateau value (reverse
transit time). Default=TSTEP).
tf Duration of the recovery ramp in seconds, from the
pulse plateau back to the initial value (forward
transit time). Default=TSTEP.
pw Pulse width (the width of the plateau portion of the
pulse) in seconds. Default=TSTEP.
per Pulse repetition period in seconds.
Default=TSTEP
Keith.