Adding Attributes

You can define default attributes for a symbol using the menu command Edit=>Attributes=>Edit Attributes. The most important attribute is called the "Prefix". This determines the basic type of symbol. If the symbol is intended to represent a SPICE primitive, the symbol should have the appropriate prefix, R for resistor, C or capacitor, M for MOSFET, etc. See the LTspice reference for a complete set of SPICE primitives available. The prefix should be 'X' if you want to use the symbol to represent a subcircuit defined in a library.

The symbol's attributes can be overridden in the instance of the symbol as a component in a schematic. For example, if you have a symbol for a MOSFET with a prefix attribute of 'M', it's possible to override the prefix to an 'X' on an instance-by-instance basis so that the transistor can be modeled as subcircuit instead.

There is a special combination of attributes that will cause a required library to be automatically included in every schematic that uses the symbol:

    Prefix: X
SpiceModel: <name of file including the spicemodel>
     Value: <What ever you want visible on the schematic>
    Value2: <The value as you want in the netlist>

Value2 would be made to coincide with a subcircuit name defined in the file including the spicemodel and may pass additional parameters to the subcircuit. When a symbol is defined in this manner, an instance of the symbol as a component on a schematic cannot be edited to have different attributes.

If you wish the symbol to represent another page of a hierarchical schematic, all attributes should be left blank the symbol type should be changed from "Cell" to "Block". No attribute values need be set.

There is a symbol attribute, ModelFile, that may be specified. This is used for the name of a file to be included in the netlist as a library. If the prefix attribute is 'X' and there is a symbol attribute SpiceModel defined that is subcircuit defined in the model file, then a drop list of all subcircuits names will be available when an instance of the symbol is edited on a schematic.