LTSpice Question Re Generating Square Pulses

I'm trying out LTSpice for the first time and was experiencing difficulty in generating a square pulse type input using the independent voltage source options.

What I wanted to do was have an input go from +15V after a few seconds to 0V with a very short fall time, then rise again to +15V after a few seconds.

The PULSE and PWL options - when plotted give me voltages ranging from +15 to -15. Obviously I don't fully understand the definitions. Perhaps someon from LT could set me straight.

Thanks in advance!

 

John,

This deck shows V1 starting at 15V and stays there for 10s.
then it goes to 0V(with a 1us fall time) and stays at 0V for
1ms. There period repeats every 5 sec. The trick here is
to invert the usual sense of on and off time. When the
pulse is on, it's doing 0V. When it's off, it's doing 15.

Hope this helps,

--Mike

*
V1 1 0 pulse(15 0 10 1u 1u 1m 5)
..tran 100
..end