Demux (Using Simulink)

Separate a vector signal into output signals.

Library

Signals & Systems

Description

The Demux block separates a vector input signal into output lines, each of which can carry a scalar or vector signal. Simulink determines the number and widths of the output signals by the Number of outputs parameter.

Scalar Number of Outputs

If the Number of outputs parameter field contains a scalar value, the block separates the input signal into that number of output signals. The widths of the output signals depend on the width of the input vector and the number of outputs:

If the input signal width is equal to the number of outputs, the block separates the input signal vector into scalar signals. In this model, the Demux block separates a three-element vector signal into three scalar signals. The Number of outputs parameter is 3.
If the input signal width is evenly divisible by the number of outputs, the block separates the input signal into vector signals of equal width. In this model, the Demux block separates a 12-element vector signal into three vector signals, each with a width of four elements.
If the input signal width is not evenly divisible by the number of outputs (and they're not the same), the block separates the input signal into vector signals of unequal width and Simulink issues a warning message. In this model, the Demux block separates a four-element vector signal into three signals. The first signal contains the first two elements of the input signal.

Vector Number of Outputs

If the Number of outputs parameter is a vector, the number of output lines is equal to the number of elements in the vector. The output signal widths depend on the input vector width and the values of the elements of the parameter. You can explicitly size output signals or let Simulink determine their widths.

If the Number of outputs vector elements are all positive values, the block generates signals with the specified widths. In this model, the input signal is a vector of width 7 and the Number of outputs parameter is [2 4 1].
If the Number of outputs vector elements include positive and -1 values, the block generates output signals with the specified widths for those outputs having positive values and dynamically sizes those outputs having
-1 values.

In this model, the input signal is a vector of width seven and the Number of outputs parameter is [-1 3 -1]. In this example, Simulink explicitly generates a three-element vector signal as the second output and dynamically sizes the other two outputs by dividing the remaining input elements as evenly as possible. In this case, the four elements divide equally.

In the next example, the Number of outputs is specified as [-1 4 -1]. This parameter causes Simulink to generate unequal output vectors.

If the Number of outputs vector elements are all -1, the number of outputs is equal to the number of vector elements, and the widths are dynamically sized. Specifying the parameter in this way is the same as specifying the parameter as a scalar whose value is the number of elements. For example, entering [-1 -1 -1] is the same as specifying a parameter value of 3.

Simulink draws the specified number of output ports on the block, resizing the block if necessary. When the number of ports is increased or decreased, ports are added or removed from the bottom of the block icon.

Using a Variable to Provide the Number of Outputs Parameter

When you specify the Number of outputs parameter as a variable, Simulink issues an error message if the variable is undefined in the workspace.

Note
Simulink hides the name of a bus selector block when you copy it from the Simulink library to a model.

Data Type Support

A Demux block accepts and outputs signals of any numeric (complex or real) and data type.

Parameters and Dialog Box

Number of outputs

The number and width of outputs. The total of the output widths must match the width of the input line.

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