Why doesn the subcircuit symbol have the same pin numbers as my favorite device package?
Spice knows nothing about pins, packages or schematics. What you see on a Spice .Subckt definition line is a list of circuit nodes that connect externally. This is a universal way of connecting a circuit. .SUBCKT subckt_Name nodeA nodeB nodeC ….. The circuit nodes are identified by a name or a number. If numbers, the subcircuit’s author may or may not have assigned numbers matching the pin numbers of some particular physical package (Spice has no standard). In 5Spice we work directly with the node numbers/names since that is the only thing that is consistent across all Spice subcircuits. This allows you to add any subcircuit to the library. The program connects the nodes to pins of the schematic’s subcircuit symbol in the order the nodes appear on the .Subckt line. The first node (nodeA in example) always connects to the symbol’s pin s1, no matter what the node’s number/name is. The second node (nodeB in example) always connects to pin s2. And so on. You can add your own descriptions
