User`s guide

Timin
g
Characteristics 7
-15
When outputs connect to analog devices, the propagation delay
is reduced by the switching times specified in the I/O
Model.
Inertial and Transport Dela
y
The simulator uses two different types of internal delay
functions when simulating the digital portion of the circuit:
inertial delay and transport delay. The application of these
concepts is embodied within the implementation of the digital
primitives within the simulator. Therefore, they are not user-
selectable.
Inertial dela
y
The simulation of a device may be described as the application
of some stimulus (S) to a function (F) and predicting the
response (R).
If this device is electrical in nature, application of the stimulus
implies that energy will be imparted to the device to cause it to
change state. The amount of such energy is a function of the
signal’s amplitude and duration. If the stimulus is applied to the
device for a length of time that is too short, the device will not
switch. The minimum duration required for an input change to
have an effect on a device’s output state is called the inertial
delay of the device. For digital simulation, all delay parameters
specified in Timing Models are considered inertial, with the
exception of the delay line primitive, DLYLINE.
To model the noise immunity behavior of digital devices
correctly, the TPWRT (Pulse Width Rejection Threshold)
parameter can be set in the digital device’s I/O Model. When
pulse width ≥ TPWRT and pulse width < propagation delay,
then the device generates either a 0-R-0, 1-F-1, or an X pulse.
This example shows normal operation in which a pulse of 20
nsec width is applied to a BUF primitive having propagation
delays of 10 nsec. TPWRT is not set.
See Input/Output
Characteristics on page 7-17 for
more information.
S
F
R