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Node and Device Naming

Xic will assign names and node numbers to the device, subcircuits and nodes in the circuit, by default. These will be unique numbers for each type of device and for each node. One problem, however, is that these numbers will change when the circuit topology is changed. Often, the SPICE output may be used by another application, that may need to access circuit node voltages, for example, in a predictable way. Thus, Xic has provision for assigning an immutable name to wire nets, and to devices and subcircuits.

By default, device names are assigned by Xic as the device key letter followed by an integer that Xic generates. This can be overridden by assigning a name property to the device. The procedure is identical to assigning the properties that we have discussed previously. The Name button in the Add menu of the Property Editor is used. Although the string that is entered as the name property can be anything, there are some very important constraints for correct SPICE output.

  1. The first letter of the name must be the same (case insensitive) as the default name. This is the `key' that identifies the type of device in SPICE.

  2. The name should be a single word containing alpha-numeric characters only.

  3. The name should be unique in the circuit.

Although Xic provides flexibility in assigning this property, SPICE simulations will fail unless these constraints are observed. Once the name property is assigned to a device, that name, rather than the default, will be used to reference the device. The name will appear in a label next to the device on-screen. As we have previously seen, the name can be modified subsequently with the label editor.

The procedure for assignment of names to subcircuits is identical. The `key' letter for subcircuits is `X'.

The node mapping editor, which appears when the nodmp button in the side menu is pressed, is used to assign names to nodes. A ``node'' is SPICE terminology for a collection of one or more device and subcircuit terminals that are connected together. Each node is given a unique number by Xic, which is used as the node ``name'' in SPICE output. The node mapping editor allows the node to have an assigned name, which will be used instead.

Full information on the node mapping editor can be found in the section describing the nodmp command (7.11). Here, we will briefly outline its use. The left panel of the node mapping editor contains a list of the circuit nodes, with the left column containing the internal number, and the right column containing the assigned name, if any. Selecting an entry in this list will cause the device terminals for that node to be listed in the right panel, and these will be highlighted in the schematic. Pressing the Rename button will prompt the user for a name for that node. This can be any word consisting of alpha-numeric characters. This word will be used in SPICE output to designate the node, rather than the number.

next up previous contents index
Next: Connectivity Overview Up: Electrical Schematic Editing Previous: Creating Subcircuits   Contents   Index
Stephen R. Whiteley 2017-03-22