In order to use Pspice, a circuit must be specified in terms of element names, element values, nodes, variable parameters, and sources. First of all, node numbers are assigned to the circuit to be simulated. Elements are connected between nodes. The node numbers to which an element is connected are specified after the name of the element. Node 0 is predefined as the ground. All nodes should be connected to at least two elements. For example in order represent a 20 kilo-ohm resistor connected between the nodes 1 and 2, it may be written as:
R1 1 2 20.0K
Circuit elements are identified by names. A name must start with a letter symbol corresponding to the element but after that it can contain either letters or numbers. For example the name of a capacitor must start with C.
The values of some circuit elements or their behaviour are dependent on other parameters, such as the initial condition of an inductor, the capacitance as a function of voltage, and the resistance as a function of temperature. There are different techniques for specifying models of sources, passive elements and active elements. For example, the model for a simple sinusoidal source is:
SIN( VO VA FREQ) where VO = offset voltage, VA = Peak voltage, FREQ = frequency in Hz.