Because setting up power and ground values and pins can be confusing
when using s2ibis2, here's how the program behaves:

I)  If the component in question  _does_not_ have a [Pin Mapping]
    section, it uses the first pin with model name POWER as the power
    connection, and the first pin with model name GND as the ground
    connection.

    A)  For pullup, pulldown, ramp or waveform curves, the power and
        ground voltages are set as follows:
    
        1)  The power pin voltage will be set by the [Pullup Reference]
            keyword.  If that keyword is not present, it will be set by
            the [Voltage Range] keyword.

        2)  The ground pin voltage will be set by the 
            [Pulldown Reference] keyword.  If that keyword is not
            present, the voltage will be set to 0 V.

    B)  For power clamp or ground clamp curves, the power and ground
        voltages are set as follows:

        1)  The power pin voltage will be set by the 
            [Power Clamp Reference] keyword.  If that keyword is not
            present, the voltage will be set by the [Voltage Range]
            keyword.

        2)  The ground pin voltage will be set by the 
            [GND Clamp Reference] keyword.  If that keyword is not
            present, the voltage will be set to 0 V.


II) If the component in question _does_ have a [Pin Mapping] section,
    the section specifies which power and ground buses the pin is
    connected to.  These power and ground buses are in turn connected
    to other pins, to which the supply voltages are attached.

    A)  For pullup, pulldown, ramp or waveform curves, the bus specified
        in the pullup_ref column of the [Pin Mapping] section is the
        power bus.  
        
        The bus specified in the pulldown_ref column of the [Pin
        Mapping] section is the ground bus.  
        
        Note that either of these may be connected to the reserved bus
        "NC", in which case the corresponding supply pin will be left
        floating.

        The voltages on these buses (if not connected to "NC") will be
        set as follows:

        1)  The power bus voltage will be set by the [Pullup Reference]
            keyword.  If that keyword is not specified, the power bus 
            voltage will be set by the [Voltage Range] keyword.

        2)  The ground bus voltage will be set by the 
            [Pulldown Reference] keyword.  If that keyword is not
            specified, the ground bus voltage will be set to 0 V.
            
    B)  For power clamp or ground clamp curves, the bus specified in the
        power_clamp_ref column of the [Pin Mapping] section is the power
        bus.  If that column is blank, the bus specified in the
        pullup_ref column is the power bus.

        The bus specified in the gnd_clamp_ref column of the [Pin
        Mapping] section is the ground bus.  If that column is blank,
        the bus specified in the pulldown_ref column is the ground bus.

        Note that either of these may be connected to the reserved bus
        "NC", in which case the corresponding supply pin will be left
        floating.

        The voltages on these buses (if not connected to "NC") will be
        set as follows:

        1)  The power bus voltage will be set by the 
            [POWER Clamp Reference] keyword.  If that keyword is not
            specified, the power bus voltage will be set by the 
            [Voltage Range] keyword.

        2)  The ground bus voltage will be set by the 
            [GND Clamp Reference] keyword.  If that keyword is not
            specified, the ground bus voltage will be set to 0 V.
