User`s guide

3 Working with Signals
3-6
The following sections explain the parameters available in this dialog box:
•“Recommended Settings for Discrete-Time Simulations”
•“Sample Time Offsets”
•“Cross-Rate Operations in Variable-Step and Fixed-Step SingleTasking
Modes”
•“Sample Time Offsets”
Recommended Settings for Discrete-Time Simulations. The recommended Solver
options
settings for DSP simulations are:
•
Type = Fixed-step discrete
•Fixed step size = auto
•Mode = SingleTasking
You can automatically set the above solver options for all new models by
running the
dspstartup M-file. See “Configuring Simulink for DSP Systems”
on page 2-11 for more information.
In
Fixed-step SingleTasking mode, discrete-time signals differ from the
prototype described in “Discrete-Time Signals” on page 3-3 by remaining
defined between sample times. For example, the representation of the
discrete-time triangle wave looks like this.
The above signal’s value at t=3.112 seconds is the same as the signal’s value at
t=3 seconds. In
Fixed-step SingleTasking mode, a signal’s sample times are
the instants where the signal is allowed to change values, rather than where
the signal is defined. Between the sample times, the signal takes on the value
at the previous sample time.
As a result, in
Fixed-step SingleTasking mode, Simulink permits cross-rate
operations such as the addition of two signals of different rates. This is
explained further in “Cross-Rate Operations in Variable-Step and Fixed-Step
SingleTasking Modes” on page 3-7.
time (s)12345670
T
s