Demux

R2026b

Extract and output elements of virtual vector signal

• 

Demux block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

Libraries:
Simulink / Commonly Used Blocks
Simulink / Signal Routing
HDL Coder / Commonly Used Blocks
HDL Coder / Signal Routing

Description

The Demux block extracts the components of an input vector signal and outputs separate signals. The output signal ports are ordered from top to bottom.

Examples

Extract Vector Elements and Distribute Evenly Across Outputs

You can use the Demux block to distribute an input signal evenly over the desired number of outputs. For an input vector of length 6, when you set the Number of outputs parameter to 3, the Demux block creates three output signals, each of size 2.

To view this behavior, open and simulate the example model.

mdl = "DemuxVectorUnspecified";
open_system(mdl)
sim(mdl);

Extract Vector Elements Using Specified Output Dimensions

When using the Demux block to extract and output elements from a vector input, you can use -1 in a vector expression to indicate that the block dynamically sizes the corresponding port. When a vector expression comprises both positive values and -1 values, the block assigns as many elements as needed to the ports with positive values. The block distributes the remaining elements as evenly as possible over the ports with -1 values.

In this example, the Number of outputs parameter of the Demux block is set to [-1, 3, -1]. Thus, the block outputs three signals where the second signal always has three elements. The sizes of the first and third signals depend on the size of the input signal. For an input vector with seven elements, the Demux block outputs two elements on the first port, three elements on the second port, and two elements on the third port.

To view this behavior, open and simulate the example model.

mdl = "DemuxVectorSpecified";
open_system(mdl)
sim(mdl);

Extended Examples

Extract Output Elements of Feedback System

Demonstrates how to extract the output elements of a state-space system that uses vector signals.

• Open Live Script

Ports

Input

Port_1 — Accept nonbus vector signal to extract and output signals from

real or complex values of any nonbus data type supported by Simulink^® software

Vector input signal from which the Demux block selects scalar signals or smaller vectors.

Data Types: single | double | half | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | enumerated | image

Output

Port_1 — Output signals extracted from input vector signal

nonbus signal with real or complex values of any data type supported by Simulink software

Output signals extracted from the input vector. The output signal ports are ordered from top to bottom. For a description of the port order for various block orientations, see Identify Port Location on Rotated or Flipped Block.

Data Types: single | double | half | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | enumerated | image

Parameters

Number of outputs — Number of outputs

2 (default) | scalar | vector

Specify the number of outputs and, optionally, the dimensionality of each output port.

The value can be a scalar specifying the number of outputs or a vector whose elements specify the widths of the block output ports. The block determines the size of its outputs from the size of the input signal and the value of the Number of outputs parameter.

If you specify a scalar for the Number of outputs parameter, and all of the output ports are connected, as you draw a new signal line close to the output side of a Demux block, the software adds a port and updates the Number of outputs parameter.

For an input vector of width n, this table describes what the block outputs.

Parameter Value	Block Output	Examples and Comments
p = n	p scalar signals	If the input is a three-element vector and you specify three outputs, the block outputs three scalar signals.
p > n	Error	This value is not supported.
p < n n mod p = 0	p vector signals each having n/p elements	If the input is a six-element vector and you specify three outputs, the block outputs three two-element vectors.
p < n n mod p = m	m vector signals each having (n/p)+1 elements and p-m signals having n/p elements	If the input is a five-element vector and you specify three outputs, the block outputs two two-element vector signals and one scalar signal.
[p1 p2 ... pm] p1+p2+...+pm=n pi > 0	m vector signals having widths p1, p2, ... pm	If the input is a five-element vector and you specify [3, 2] as the output, the block outputs three of the input elements on one port and the other two elements on the other port.
An array that has one or more of m elements with a value of -1, which specifies that the software infers the size for the element. For example, suppose that you have a four-element array with a total width of 14 and you specify the parameter to be [p1 p2 -1 p4]. The value for the third element (the -1 element) is 14 - (p1 + p2 + p4)	m vector signals	If pi is greater than zero, the corresponding output has width pi. If pi is -1, the width of the corresponding output is computed dynamically.
[p1 p2 ... pm] p1+p2+...+pm!=n pi = > 0	Error	This value is not supported.

If you specify a number of outputs that is smaller than the number of input elements, the block distributes the elements as evenly as possible over the outputs.

Specifying a nondouble value, such as single(3), is not supported.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter:	Outputs
Values:	'2' (default) | scalar in quotes | vector in quotes
Data Types:	char | string

Example: set_param(gcb,'Outputs','4')

Display option — Displayed block icon

bar (default) | none

By default, the block icon is a solid bar of the block foreground color. To display the icon as a box containing the block type name, select none.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter:	DisplayOption
Values:	'bar' (default) | 'none'

Example: set_param(gcb,'DisplayOption','none')

Block Characteristics

Data Types	Boolean | double | enumerated | fixed point | half | image | integer | single
Direct Feedthrough	yes
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

Programmatic Use: Add Block

To add the block programmatically, use the add_block function with one of these library block paths as the source.

"simulink/Commonly Used Blocks/Demux"

"simulink/Signal Routing/Demux"

"hdlsllib/Commonly Used Blocks/Demux"

"hdlsllib/Signal Routing/Demux"

Example: add_block("simulink/Commonly Used Blocks/Demux","myModel/myBlock",MakeNameUnique="on")

For information about programmatic access to individual block parameters, see the Programmatic Use section of parameter descriptions on this page.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

Actual data type or capability support depends on block implementation.

HDL Code Generation

Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.

HDL Coder™ provides additional configuration options that affect HDL implementation and synthesized logic.

HDL Architecture

This block has one default HDL architecture.

HDL Block Properties

ConstrainedOutputPipeline	Number of registers to place at the outputs by moving existing delays in the design. Distributed pipelining does not redistribute these registers. The default value is 0. For more details, see ConstrainedOutputPipeline (HDL Coder).
InputPipeline	Number of input pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default value is 0. For more details, see InputPipeline (HDL Coder).
OutputPipeline	Number of output pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default value is 0. For more details, see OutputPipeline (HDL Coder).
SynthesisAttributes	Specifies the synthesis attributes for the blocks and block output signals in the model. The generated HDL code contains these attributes. For more information, see SynthesisAttributes (HDL Coder).

Complex Data Support

This block supports code generation for complex signals.

Fixed-Point Conversion

Design and simulate fixed-point systems using Fixed-Point Designer™.

Actual data type or capability support depends on block implementation.

Version History

Introduced before R2006a

R2026a: Specify synthesis attributes for blocks and block output signals

Use the SynthesisAttributes HDL block property to specify the synthesis attributes for the block and its output signals. HDL Coder includes these attributes in the generated HDL code.