Specify Sample Time
Designate Sample Times
Simulink® allows you to specify a block sample time directly as a numerical
value or symbolically by defining a sample time vector. Sample time value must be a
double or a two-element array of
that contains the sample time period and offset. In the case of a discrete sample
time, the vector is [
, ] where
is the sampling period and
is the initial time offset. For
example, consider a discrete model that produces its outputs every two seconds. If
your base time unit is seconds, you can directly set the discrete sample time by
specifying the numerical value of
2 as the
SampleTime parameter. Because the offset value is zero, you
do not need to specify it; however, you can enter [
2,0] in the
Sample time field.
For nondiscrete blocks, the components of the vector are symbolic values that
represent one of the types in Types of Sample Time. The following table
summarizes these types and the corresponding sample time values. The table also
defines the explicit nature of each sample time type and designates the associated
color and annotation. Because an inherited sample
time is explicit, you can specify it as
[-1, 0] or
-1. Whereas, a triggered sample time is implicit; only
Simulink can assign the sample time of
[-1, -1]. (For more
information about colors and annotations, see View Sample Time Information.)
Designations of Sample Time Information
|Sample Time Type||Sample Time||Annotation||Explicit|
|Discrete||[Ts, To]||D1, D2, D3, D4, D5, D6, D7,... Di||Yes|
|Fixed in minor step||[0, 1]||FiM||Yes|
|Variable||[–2,Tvo]||V1, V2,... Vi||No|
|Asynchronous||[–1, –n]||A1, A2,... Ai||No|
|Initialize model wide event||[Inf,1]||IE|
|Terminate model wide event||[Inf, 2]||TE|
|Resent model wide event||[Inf, 3, 4, … ]||RE1, RE2, RE3...|
|Union||[NaN, NaN]||U1, U2, U3...|
|Aperiodic Partitions||[1, -30]||AP1, AP2, AP3...|
The color that is assigned to each block depends on its sample time relative to other sample times in the model. This means that the same sample time may be assigned different colors in a parent model and in models that it references. (See Model References.)
For example, suppose that a model defines three sample times:
suppose that it references a model that defines two sample times:
3. In this case, blocks operating at
2 sample rate appear as green in the parent model and as red
in the referenced model.
It is important to note that Mux and Demux blocks are simply grouping operators; signals passing through them retain their timing information. For this reason, the lines emanating from a Demux block can have different colors if they are driven by sources having different sample times. In this case, the Mux and Demux blocks are color coded as hybrids (yellow) to indicate that they handle signals with multiple rates.
Similarly, Subsystem blocks that contain blocks with differing sample times are also colored as hybrids, because there is no single rate associated with them. If all the blocks within a subsystem run at a single rate, the Subsystem block is colored according to that rate.
You can use the explicit sample time values in this table to specify sample times interactively or programmatically for either block-based or port-based sample times.
The following model, serves as a reference for this section.
In this example, set the sample time of the input sine wave signal to
0.1. The goal is to achieve an output sample time of
0.2. The Rate Transition block serves as a
zero-order hold. The resulting block diagram after setting the sample times and
simulating the model is shown in the following figure. (The colors and annotations
indicate that this is a discrete model.)
ex_specify_sample_time after Setting Sample Times
Specify Block-Based Sample Times Interactively
To set the sample time of a block interactively:
In the Simulink model window, double-click the block. The block parameter dialog box opens.
Enter the sample time in the Sample time field.
Following is a figure of a parameters dialog box for the Sine Wave
block after entering
0.1 in the Sample time field.
To specify and inspect block-based sample times throughout a model, consider using
the Model Data Editor (on the Modeling tab, click
Model Data Editor). On the
Inports/Outports, Signals, and
Data Stores tabs, set the Change view
drop-down list to
Design and use the Sample
Time column. For more information, see Model Data
Specify Port-Based Sample Times Interactively
The Rate Transition block has port-based sample times. You can set the output port sample time interactively by completing the following steps:
Double-click the Rate Transition block. The parameters dialog box opens.
Leave the drop-down menu choice of the Output port sample time options as
-1in the Output port sample time field with
For more information about the sample time options in the Rate Transition parameters dialog box, see the Rate Transition reference page.
Specify Block-Based Sample Times Programmatically
To set a block sample time programmatically, set its
parameter to the desired sample time using the
command. For example, to set the sample time of the Gain block in the
Specify_Sample_Time model to inherited (
-1), enter the following
As with interactive specification, you can enter just the first vector component if the second component is zero.
Specify Port-Based Sample Times Programmatically
To set the output port sample time of the Rate Transition block to
0.2, use the
set_param command with the
set_param('Specify_Sample_Time/Rate Transition',... 'OutPortSampleTime', '0.2')
Access Sample Time Information Programmatically
To access all sample times associated with a model, use the API
To access the sample time of a single block, use the API
Specify Sample Times for a Custom Block
You can design custom blocks so that the input and output ports operate at different sample time rates. For information on specifying block-based and port-based sample times for S-functions, see Specify S-Function Sample Times .
Determining Sample Time Units
Since the execution of a Simulink model is not dependent on a specific set of units, you must determine
the appropriate base time unit for your application and set the sample time values
accordingly. For example, if your base time unit is second, then you would represent
a sample time of
0.5 second by setting the sample time to
Change the Sample Time After Simulation Start Time
To change a sample time after simulation begins, you must stop the simulation,
SampleTime parameter, and then restart