The Alter Command

An alter command temporarily changes the value of any element or parameter in a MAST template. It is used to make a change in a template description so that a simulation can be re-executed without reloading the original circuit. The alter command cannot be used to make a change that modifies the topology of a design.

Alter commands are used in IC-CAP Saber simulations when the Circuit Description and Setup information, other than the sweep limits, remain unchanged from the previous simulation.

If only parameter values in the Device Parameters table or Model Parameters table are changed, IC-CAP will not restart the Saber simulator and reload the circuit. Instead, IC-CAP generates alter commands for every parameter, then re-executes the simulation commands. The USE_ALTER variable can be specified and set to No to override this behavior. In this case, Saber is restarted with every simulation whether or not the Circuit Description or Setup was changed. If the USE_ALTER variable does not exist, IC-CAP behaves as if the variable were set to Yes.

After a successful simulation, if a resistor is changed from a non-zero to zero value, Saber collapses the nodes. This causes an implicit topological change in the circuit that is not recognized by IC-CAP since the Circuit Description or Setup information has not been changed. Turn the USE_ALTER variable off by setting it to NO to allow IC-CAP to restart the Saber simulator and reload the altered circuit.