Delay

Delay input signal by fixed or variable sample periods

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Libraries:
Simulink / Commonly Used Blocks
Simulink / Discrete
DSP System Toolbox / Signal Operations
HDL Coder / Commonly Used Blocks
HDL Coder / Discrete

Description

The Delay block outputs the input of the block after a delay. The block determines the delay time based on the value of the Delay length parameter. The block supports:

• Variable delay length

• Specification of the initial condition from an input port

• State storage

• Using a circular buffer instead of an array buffer for state storage

• Resetting the state to the initial condition with an external reset signal

• Controlling execution of the block at every time step with an external enable signal

The initial block output depends on several factors such as the Initial condition parameter and the simulation start time. For more information, see Initial Block Output. The External reset parameter determines if the block output resets to the initial condition on triggering. The Show enable port parameter determines if the block execution is controlled in every time step by an external enable signal.

Initial Block Output

The output in the first few time steps of the simulation depends on the block sample time, the delay length, and the simulation start time. The block supports specifying or inheriting discrete sample times to determine the time interval between samples. For more information, see Specify Sample Time.

The table shows the Delay block output for the first few time steps with these settings. The block inherits a discrete sample time as [Tsampling,Toffset], where Tsampling is the sampling period and Toffset is the initial time offset. n is the value of the Delay length parameter and Tstart is the simulation start time for the model

Simulation Time Range	Block Output
(Tstart) to (Tstart + Toffset)	Zero
(Tstart + Toffset) to (Tstart + Toffset + n * Tsampling)	Initial condition parameter
After (Tstart + Toffset + n * Tsampling)	Input signal

Behavior with External Enable Signal

Selecting the Show enable port check box enables the Enable port. If the enable port is enabled, the block operates in this order

1. Checks if the enable condition is satisfied.

2. If the reset port is enabled, checks the reset condition.

3. Performs the Delay block functionality.

The block has this operation with the Enable port:

• At the first block enable, the block output is the initial condition value (x0).

• For consecutive enable signals, the block takes the last state of the input signal u.

• If the port is not enabled at the start of simulation, the Delay block outputs 0.

• During simulation, if the port becomes disabled after having been enabled, the block does not execute and holds its last value.

Variable-Size Support

The Delay block provides the following support for variable-size signals:

• The data input port u accepts variable-size signals. The other input ports do not accept variable-size signals.

• The output port has the same signal dimensions as the data input port u for variable-size inputs.

The rules that apply to variable-size signals depend on the input processing mode of the Delay block.

Input Processing Mode	Rules for Variable-Size Signal Support
Elements as channels (sample based)	The signal dimensions change only during state reset when the block is enabled. The initial condition must be scalar.
Columns as channels (frame based)	No support

Bus Support

The Delay block provides the following support for bus signals:

• The data input u accepts virtual and nonvirtual bus signals. Other than input port x0, the other input ports do not accept bus signals.

• The initial condition x0 port accepts nonvirtual bus signals.

• The output port has the same bus type as the data input port u for bus inputs.

• Buses work with:

  • Sample-based and frame-based processing

  • Fixed and variable delay length

  • Array and circular buffers

To use a bus signal as the input to a Delay block, specify the initial condition on the dialog box or through the x0 port. Support for virtual and nonvirtual buses depends on the initial condition that you specify and whether the State name parameter is empty or not. For the x0 input port, only nonvirtual buses are supported.

Initial Condition	State Name
	Empty	Not Empty
Zero	Virtual and nonvirtual bus support	Nonvirtual bus support only
Nonzero scalar	Virtual and nonvirtual bus support	No bus support
Nonscalar	No bus support	No bus support
Structure	Virtual and nonvirtual bus support	Nonvirtual bus support only
Partial structure	Virtual and nonvirtual bus support	Nonvirtual bus support only

String Support

The Delay block can accept and output string data type only if:

• The block is configured for the default value of the Initial condition parameter (0).

• The Delay length value is 1 or less.

Examples

Using Variable-Size Signals on the Delay Block

This example shows how the Delay block supports variable-size signals for sample-based processing. The Switch block controls whether the input signal to the enabled subsystem is a 3-by-3 or 3-by-2 matrix.

The Delay block appears inside the enabled subsystem.

The model follows these rules for variable-size signals while using sample-based processing.

• Signal dimensions change only during state reset when the block is enabled.

• Initial condition must be scalar.

The rules are implemented by these blocks.

• Enable block sets Propagate sizes of variable-size signals to Only when enabling.

• Delay block sets the Initial condition to the scalar value 0.0.

Buses with the Delay Block for Frame-Based Processing

This example shows how the Delay block supports buses for frame-based processing.

Each Constant block supplies an input signal to the Bus Creator block, which outputs a two-dimensional bus. After the Delay block delays the bus by three sample periods, the Bus Selector block separates the bus back into the two original signals.

The model follows these rules for buses:

• For the initial condition, set the value on the dialog box.

• For frame-based processing, signal dimensions of the data input port u cannot be larger than two.

The model implements the rules by:

• Setting Initial condition to a scalar value of 0.

• Setting bus input to the Delay block as two dimensions.

Control Execution of Delay Block with Enable Port

This example shows how you can enable or disable the execution of the Delay block using an enable port. In this model, a ramp input signal feeds into a Delay block. The execution of the block is controlled by an enabling signal from the Pulse Generator block.

The blue line shows that the Delay block outputs the input signal value delayed by one time step while the enabling signal has a value of one. At t=5 the enabling signal transitions to zero and the Delay block stops executing. The output is held at the last value until the block is enabled again.

Ports

Input

u — Data input signal

scalar | vector

Input data signal delayed according to parameters settings.

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

d — Delay length

scalar

Delay length specified as inherited from an input port. Enabled when you select the Delay length: Source parameter as Input port.

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

Enable — External enable signal

scalar

Enable signal that enables or disables execution of the block. To create this port, select the Show enable port parameter.

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

External reset — External reset signal

scalar

External signal that resets execution of the block to the initial condition. To create this port, select the External reset parameter.

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

x0 — Initial condition

scalar | vector

Initial condition specified as inherited from an input port. Enabled when you select the Initial Condition: Source parameter as Input port.

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

Output

Port_1 — Output signal

scalar | vector

Output signal that is the input signal delayed by the length of time specified by the parameter Delay length. The initial value of the output signal depends on several conditions. See Initial Block Output.

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

Parameters

Main

Delay length — Delay length

Dialog (default) | Input port

Specify whether to enter the delay length directly on the dialog box (fixed delay) or to inherit the delay from an input port (variable delay).

• If you set Source to Dialog, enter the delay length in the edit field under Value.

• If you set Source to Input port, verify that an upstream signal supplies a delay length for the d input port. You can also specify its maximum value by specifying the parameter Upper limit.

Specify the scalar delay length as a real, non-negative integer. An out-of-range or non-integer value in the dialog box (fixed delay) returns an error. An out-of-range value from an input port (variable delay) casts it into the range. A noninteger value from an input port (variable delay) truncates it to the integer.

Programmatic Use

Block Parameter: DelayLengthSource

Type: character vector

Values: 'Dialog' | 'Input port'

Default: 'Dialog'

Block Parameter: DelayLength

Type: character vector

Values: scalar

Default: '2'

Block Parameter: DelayLengthUpperLimit

Type: character vector

Values: scalar

Default: '100'

Initial condition — Initial condition

Dialog (default) | Input port

Specify whether to enter the initial condition directly on the dialog box or to inherit the initial condition from an input port.

• If you set Source to Dialog, enter the initial condition in the edit field under Value.

• If you set Source to Input port, verify that an upstream signal supplies an initial condition for the x0 input port.

Simulink^® converts offline the data type of Initial condition to the data type of the input signal u using a round-to-nearest operation and saturation.

Note

When State name must resolve to Simulink signal object is selected on the State Attributes pane, the block copies the initial value of the signal object to the Initial condition parameter. However, when the source for Initial condition is Input port, the block ignores the initial value of the signal object.

Programmatic Use

Block Parameter: InitialConditionSource

Type: character vector

Values: 'Dialog' | 'Input port'

Default: 'Dialog'

Block Parameter: InitialCondition

Type: character vector

Values: scalar

Default: '0.0'

Input processing — Specify sample- or frame-based processing

Elements as channels (sample based) (default) | Columns as channels (frame based)

Specify whether the block performs sample- or frame-based processing:

• Columns as channels (frame based) — Treat each column of the input as a separate channel (frame-based processing).

  Note

  Frame-based processing requires a DSP System Toolbox™ license.

  For more information, see Sample- and Frame-Based Concepts (DSP System Toolbox).

• Elements as channels (sample based) — Treat each element of the input as a separate channel (sample-based processing).

Use Input processing to specify whether the block performs sample- or frame-based processing. For more information about these two processing modes, see Sample- and Frame-Based Concepts (DSP System Toolbox).

Programmatic Use

Block Parameter: InputProcessing

Type: character vector

Values: 'Columns as channels (frame based)' | 'Elements as channels (sample based)'

Default: 'Elements as channels (sample based)'

Use circular buffer for state — Circular buffer for storing state

off (default) | on

Select to use a circular buffer for storing the state in simulation and code generation. Otherwise, an array buffer stores the state.

Using a circular buffer can improve execution speed when the delay length is large. For an array buffer, the number of copy operations increases as the delay length goes up. For a circular buffer, the number of copy operations is constant for increasing delay length.

If one of the following conditions is true, an array buffer always stores the state because a circular buffer does not improve execution speed.

• For sample-based signals, the delay length is 1.

• For frame-based signals, the delay length is no larger than the frame size.

Programmatic Use

Block Parameter: UseCircularBuffer

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Prevent direct feedthrough — Prevent direct feedthrough

off (default) | on

Select to increase the delay length from zero to the lower limit for the Input processing mode.

• For sample-based signals, increase the minimum delay length to 1.

• For frame-based signals, increase the minimum delay length to the frame length.

Selecting this check box prevents direct feedthrough from the input port, u, to the output port. However, this check box cannot prevent direct feedthrough from the initial condition port, x0, to the output port.

Dependency

To enable this parameter, set Delay length: Source to Input port.

Programmatic Use

Block Parameter: PreventDirectFeedthrough

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Remove delay length check in generated code — Remove delay length out-of-range check

off (default) | on

Select to remove code that checks for out-of-range delay length.

Check Box	Result	When to Use
Selected	Generated code does not include conditional statements to check for out-of-range delay length.	For code efficiency
Cleared	Generated code includes conditional statements to check for out-of-range delay length.	For safety-critical applications

Dependency

To enable this parameter, set Delay length: Source to Input port.

Programmatic Use

Block Parameter: RemoveDelayLengthCheckInGeneratedCode

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Diagnostic for delay length — Diagnostic checks for delay length

None (default) | Warning | Error

Specify whether to produce a warning or error when the input d is less than the lower limit or greater than the Delay length: Upper limit. The lower limit depends on the setting for Prevent direct feedthrough.

• If the check box is cleared, the lower limit is zero.

• If the check box is selected, the lower limit is 1 for sample-based signals and frame length for frame-based signals.

Options for the diagnostic include:

• None — Simulink software takes no action.

• Warning — Simulink software displays a warning and continues the simulation.

• Error — Simulink software terminates the simulation and displays an error.

Dependency

To enable this parameter, set Delay length: Source to Input port.

Programmatic Use

Block Parameter: DiagnosticForDelayLength

Type: character vector

Values: 'None' | 'Warning' | 'Error'

Default: 'None'

Show enable port — Create enable port

off (default) | on

Select to control execution of this block with an enable port. The block is considered enabled when the input to this port is nonzero, and is disabled when the input is 0. The value of the input is checked at the same time step as the block execution.

Programmatic Use

Block Parameter: ShowEnablePort

Type: character vector

Values: 'off' | 'on'

Default: 'off'

External reset — External state reset

None (default) | Rising | Falling | Either | Level | Level hold

Specify the trigger event to use to reset the states to the initial conditions.

Reset Mode	Behavior
None	No reset
Rising	Reset on a rising edge
Falling	Reset on a falling edge
Either	Reset on either a rising or falling edge
Level	Reset in either of these cases: When the reset signal is nonzero at the current time step When the reset signal value changes from nonzero at the previous time step to zero at the current time step
Level hold	Reset when the reset signal is nonzero at the current time step

Programmatic Use

Block Parameter: ExternalReset

Type: character vector

Values: 'None' | 'Rising' | 'Falling' | 'Either' | 'Level' | 'Level hold'

Default: 'None'

Sample time (-1 for inherited) — Discrete interval between sample time hits

-1 (default) | scalar

Specify the time interval between samples. To inherit the sample time, set this parameter to -1. This block supports discrete sample time, but not continuous sample time.

Programmatic Use

Block Parameter: SampleTime

Type: character vector

Value: real scalar

Default: '-1'

State Attributes

State name — Unique name for block state

'' (default) | alphanumeric string

Use this parameter to assign a unique name to the block state. The default is ' '. When this field is blank, no name is assigned. When using this parameter, remember these considerations:

• A valid identifier starts with an alphabetic or underscore character, followed by alphanumeric or underscore characters.

• The state name applies only to the selected block.

This parameter enables State name must resolve to Simulink signal object when you click Apply.

For more information, see C Data Code Interface Configuration for Model Interface Elements (Simulink Coder).

Programmatic Use

Block Parameter: StateName

Type: character vector

Values: unique name

Default: ''

State name must resolve to Simulink signal object — Require state name resolve to a signal object

off (default) | on

Select this check box to require that the state name resolves to a Simulink signal object.

Dependencies

To enable this parameter, specify a value for State name. This parameter appears only if you set the model configuration parameter Signal resolution to a value other than None.

Programmatic Use

Block Parameter: StateMustResolveToSignalObject

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Block Characteristics

Data Types	Boolean | bus | double | enumerated | fixed point | half | image | integer | single | string
Direct Feedthrough	noa
Multidimensional Signals	yes
Variable-Size Signals	yes
Zero-Crossing Detection	no
a Direct feedthrough characteristics for this block depend on block parameter values.

More About

Model Coverage

If you have a Simulink Coverage™ license, the Delay block receives decision coverage if you set the External reset parameter to any option except for None, or if you select the Show enable port parameter. If your model uses a State Control (HDL Coder) block, you cannot collect coverage for External reset and Enable ports when the State control parameter is Synchronous.

For the External reset parameter, decision coverage measures a true outcome for time steps where the block resets and a false outcome for time steps where the block does not reset. To receive 100% decision coverage, the block must reset for at least one time step and not reset for at least one time step.

For the Show enable port parameter, decision coverage measures a true outcome for time steps where the block is enabled and a false outcome for time steps where the block is not enabled. To receive 100% decision coverage, the block must be enabled for at least one time step and not enabled for at least one time step.

Extended Capabilities

C/C++ Code Generation

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

Generated code relies on memcpy or memset functions (string.h) under certain conditions.

HDL Code Generation

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

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

Block Parameter Setting	Description
Set External reset to Level.	Generates a reset port in the HDL code.
Select Show enable port.	Generates an enable port in the HDL code.
For Initial condition, set Source to Dialog and enter the value.	Specifies an initial condition for the block.
Set Input processing to Columns as channels (frame based) or Elements as channels (sample based).	Expects vector input data, where each element of the vector represents a sample in time.

Additional Settings When Using State Control Block

If you use a State Control block with the Delay block inside a subsystem in your Simulink model, use these additional settings.

Block Parameter Setting	Description
Set External reset to Level hold for Synchronous mode and Level for Classic mode of the State Control block.	Generates a reset port in the HDL code.
Set Delay length to zero for a Delay block with an external enable port.	Treated as a wire in only Synchronous mode of the State Control block.
Set Delay length to zero for a Delay block with an external reset port.	Treated as a wire in Synchronous and Classic modes of the State Control block.

For more information about the State Control block, see State Control (HDL Coder).

HDL Architecture

This block has one default HDL architecture.

HDL Block Properties

AllowDelayDistribution	Allow delay to be distributed or absorbed during the distributed pipelining and delay absorption optimizations. The default is inherit. For more details, see AllowDelayDistribution (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 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 is 0. For more details, see OutputPipeline (HDL Coder).
ResetType	Suppress reset logic generation. The default is default, which generates reset logic. See also ResetType (HDL Coder).
UseRAM	Map delays to RAM instead of registers. The default is off. See also UseRAM (HDL Coder).

Variable Integer Delay Support

• You can generate HDL code for the Delay block that has Delay Length set through the Input port. Input delay length can be integer types or floating-point types.

• The code generation supports positive integer values at the 'd' port of the delay block. The delay length set through the input port must be between 0 and Upper limit, specified in the Block Parameters dialog box.

• For negative delay length values, HDL Coder translates these negative delay length to 0.

• Similarly, if you specify delay length greater than the upper limit, HDL Coder translates the delay length to the Upper limit value.

• Upper limit range is defined by the range of the delay length input data type. For example, if you specify delay length input data type as uint8, then the upper limit must not exceed 255.

• You can use enable and reset ports for the variable integer Delay block.

Complex Data Support

This block supports code generation for complex signals.

Use Structures as Initial Values

You can generate HDL code for Delay blocks that use structures to specify the initial conditions for the Delay block. When you use bus input for a Delay block in your model, you can set initial condition for the delay block with a structure value to initialize the bus delay.

To specify initial conditions defined by structures:

1. Define a structure in the model workspace, MATLAB^® base workspace, mask workspace, or Simulink data dictionary.

2. Assign the initial condition value to this structure.

3. Set the Initial Condition parameter to Dialog and input the structure in the Value field.

You also use structures as the initial values in other delay blocks, including the Unit Delay and Tapped Delay blocks

Restrictions

• For Initial condition, Source set to Input port is not supported for HDL code generation.

• HDL code generation supports only the Boolean data type at the Reset and Enable ports.

• HDL Block Property UseRAM for RAM mapping is not supported for Delay block that has Delay Length set through the Input port.

• The Delay block that has Delay Length set through the Input port does not support bus and matrix data input for HDL code generation.

PLC Code Generation
Generate Structured Text code using Simulink® PLC Coder™.

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

Version History

Introduced before R2006a