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Unit Delay With Preview Resettable (Obsolete)

Output signal and signal delayed by one sample period, with external reset



The Unit Delay With Preview Resettable 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 Resettable block continue to work for backward compatibility.

  • Unit Delay With Preview Resettable (Obsolete) block


Additional Math & Discrete / Additional Discrete (until R2016b)


The Unit Delay With Preview Resettable block supports calculations that have feedback and depend on the current input. The block can reset its state based on a reset signal R.

The block has two input ports: one for the input signal u and one for the external reset signal R.

When the reset signal R is false, the first port outputs the signal and the second port outputs the signal delayed by one sample period.

When the reset signal R is true, the block resets the current state to the initial condition given by the Initial condition parameter. The first output signal is forced to equal the initial condition. The second output signal is not affected until one time step later.

This reset 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 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 Resettable 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.


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.


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


Variable-Size Signals


Zero-Crossing Detection


Code Generation


Version History

Introduced before R2006a