In simulink, there is no model of a pulse generator which generates only single pulse. This model outputs a single pulse. The parametres of the pulse which can be set by the user are:

Start Time
Stop Time
Pulse Amplitude with respect to Ground
Normal Level

"Normal Level" determines the Base Level of the signal and "Pulse Amplitude with respect to Ground" defines the level of the signal with respect to ground when the pulse has arrived.

For example:
The following parametres settings produces (outputs) a pulse shown in screenshot.

Start Time: 5
Stop Time: 6
Pulse Amplitude with respect to Ground: 9.25
Normal Level: 5.75