Making a Preliminary Pass (.NODESET)
The .NODESET statement helps the program find the DC or initial transient solution by making a preliminary pass with the specified nodes held to the given voltages. The restriction is then released and the iteration continues to the true solution. The only purpose of the .NODESET statement is to help DC convergence; it does not affect final bias solution (except for multi-stable circuits). This statement may be necessary for convergence on bistable or astable circuits. Generally, this statement should not be necessary.
.NODESET V(NODNUM)=VAL V(NODNUM)=VAL ...
Example:
.NODESET V(12)=4.5 V(4)=2.23 .NODESET V([VCOIN])=2.5V V([PYOUT])=2.5V V([N4N7])=2.5V
NOTE: As shown in the second example, always use square brackets around node names in a .NODESET statement.
Setting Transient Initial Conditions (.IC)
The .IC statement is used for setting transient initial conditions.
.IC V(NODNUM)=VAL V(NODNUM)=VAL ...
Example:
.IC V(11)=5 V(4)=-5 V(2)=2.2
.IC V(3)=5 V(2)=0 V([N18])=5 V(1)=12
NOTE: As shown in the second example, node names must be enclosed in square brackets.
The .IC statement has two different interpretations, depending on whether the UIC parameter is specified on the .TRAN statement. The two interpretations of this statement are as follows:
1. When the UIC parameter is specified on the .TRAN statement, then the node voltages specified on the .IC statement are used to compute the capacitor, diode, BJT, JFET, and MOSFET initial conditions. This is equivalent to specifying the IC=... parameter on each device statement, but is more convenient. The IC=... parameter can still be specified and takes precedence over the .IC values. Since no DC bias (initial transient) solution is computed before the transient analysis, you should specify all DC source voltages on the .IC statement if they are to be used to compute device initial conditions.
2. When the UIC parameter is not specified on the .TRAN statement, the DC bias (initial transient) solution is computed before the transient analysis. In this case, the node voltages specified on the .IC statement are forced to the desired initial values during the bias solution. During transient analysis, the constraint on these node voltages is removed.
Refer to the section Convergence to a DC or Transient Analysis Solution for detailed information.