User`s guide

7
-
6 Di
g
ital Device Modelin
g
The format for digital primitives is similar to that for analog
devices. One difference is that most digital primitives require
two models instead of one:
• The Timing Model, which specifies propagation delays and
timing constraints such as setup and hold times.
• The I/O Model, which specifies information specific to the
device’s input/output characteristics.
The reason for having two models is that, while timing
information is specific to a device, the input/output
characteristics are specific to a whole logic family. Thus, many
devices in the same family reference the same I/O Model, but
each device has its own Timing Model.
Figure 7-1 presents an overview of a digital device definition in
terms of its primitives and underlying model attributes. These
models are discussed further on Timing Model
on page 7-11 and
Input/Output Model
on page 7-17.
Di
g
ital primitive s
y
ntax
The general digital primitive format is shown below.
U<name> <primitive type> [( <parameter value>* )]
+ <digital power node> <digital ground node>
+ <node>*
+ <Timing Model name> <I/O Model name>
+ [MNTYMXDLY=<delay select value>]
+ [IO_LEVEL=<interface subckt select value>]
where
<primitive type> [( <parameter value>* )]
is the type of digital device, such as NAND, JKFF, or INV. It is
followed by zero or more parameters specific to the primitive
type, such as number of inputs. The number and meaning of the
parameters depends on the primitive type.
For specific information on each
primitive type see the online
MicroSim PSpice A/D Reference
Manual
.
Note that some di
g
ital primitives,
such as pullups, do not have
Timin
g
Models. See Timing
Model on page 7-11 for more
information.