Unit Delay With Preview Enabled (Obsolete)

Output signal and signal delayed by one sample period, if external enable signal is on

Compatibility

Note

The Unit Delay With Preview Enabled block is not recommended. This block was removed from the Discrete library in R2016b. In new models, use the Delay block (with parameters set appropriately). Existing models that contain the Unit Delay With Preview Enabled block continue to work for backward compatibility.

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Library

Additional Math & Discrete / Additional Discrete (until R2016b)

Description

The Unit Delay With Preview Enabled block supports calculations that have feedback and depend on the current input.

The block has two input ports: one for the input signal u and one for the external enable signal E.

When the enable signal E is on, the first port outputs the signal and the second port outputs the signal delayed by one sample period. When the enable signal E is off, the block is disabled, and the state and output values do not change, except during resets.

The enable signal is on when E is not 0, and off when E is 0. This enable action is vectorized and supports scalar expansion.

Having two outputs is useful for implementing recursive calculations where the result includes the most recent inputs. The second output can feed back into calculations of the block's inputs without causing an algebraic loop. Meanwhile, the first output shows the most up-to-date calculations.

You specify the block output for the first sampling period with the value of the Initial condition parameter.

You specify the time between samples with the Sample time parameter. A setting of -1 means that the block inherits the Sample time.

Data Type Support

The Unit Delay With Preview Enabled block accepts signals of the following data types:

• Floating point

• Built-in integer

• Fixed point

• Boolean

• Enumerated

The outputs have the same data type as the input u. For enumerated signals, the Initial condition must be of the same enumerated type as the input u.

For more information, see Data Types Supported by Simulink in the Simulink^® documentation.

Parameters

Initial condition

Specify the initial output of the simulation.

Sample time

Specify the time interval between samples. To inherit the sample time, set this parameter to -1. See Specify Sample Time in the online documentation for more information.

Characteristics

Direct Feedthrough	Yes, to first output port No, to second output port
Sample Time	Specified in the Sample time parameter
Scalar Expansion	Yes
Zero-Crossing Detection	No

Data Types	Double | Single | Boolean | Base Integer | Fixed-Point | Enumerated
Sample Time	Specified in the Sample time parameter
Direct Feedthrough	Yes, to first output port No, to second output port
Multidimensional Signals	No
Variable-Size Signals	No
Zero-Crossing Detection	No
Code Generation	Yes