Specifications

72 Chapter 4—Simulation
Input Signal Values
For all device types except switches, the signal values High Impedance and
Conflict are treated as Don’t Know when applied to a device input. When a
device is first created, all input signals take the High Impedance state, and
outputs are set depending on their type—normally to the Don’t Know state.
Thus an unused input pin will appear as an unknown input to a device,
which may affect its output level.
As with real circuits, all unused inputs should be connected to a high or low
level as appropriate. This can be done by naming the pin signal either “0”
or “1”, by using a power or ground symbol, or by using a pullup resistor to
set a high level. See more information on logic states in other parts of this
chapter.
Device Pin Types
Every device pin has a characteristic known as its pin type—for example,
input or output. The pin type is set when the part entry in the library is cre-
ated, and cannot be changed for individual device pins on the schematic.
Correct pin type settings are crucial to correct and efficient operation of the
simulator.
The pin type is used by the simulator to determine the direction of signal
flow and to set the output values that are allowable on a given output pin.
 For detailed information on the available pin types and how they affect
the simulation see Appendix B, Device Pin Types. For procedures for
setting pin types when creating a symbol see Chapter 11, Device
Symbol Editing.
Device Pin Inversion
The logic of any pin on any device can be inverted by placing a non–empty
value in the Invert.Pin attribute field of the pin. When this is done, any
value passing into or out from that pin will be inverted. This applies to
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