User`s guide

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2 Di
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ital Device Modelin
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Introduction
The standard symbol libraries contain a comprehensive set of
digital parts in many different technologies. Each digital part is
described electrically by a digital device model in the form of a
subcircuit definition stored in a model library. The
corresponding subcircuit name is defined by the part’s MODEL
attribute value. Other attributes—MNTYMXDLY, IO_LEVEL,
and the IPIN(<pin name>) set—are passed to the subcircuit,
thus providing a high-level means for influencing the behavior
of the digital device model.
Generally, the digital parts provided in the symbol libraries are
satisfactory for most circuit designs. However, if your design
requires digital parts that are not already provided in the
standard Symbol and model libraries, you will need to define
digital device models corresponding to the new digital part
symbols.
A complete digital device model has three main characteristics:
• Functional behavior: described by the gate-level and
behavioral digital primitives comprising the subcircuit.
• I/O behavior: described by the I/O Model, interface
subcircuits, and power supplies related to a logic family.
• Timing behavior: described by one or more Timing Models,
pin-to-pin delay primitives, or constraint checker
primitives.
These characteristics are described in this chapter with a running
example demonstrating the use of gate-level primitives.