Detect Fall Negative - Detect falling edge when signal value decreases to strictly negative value, and its previous value was nonnegative

Library

Logic and Bit Operations

Description

The Detect Fall Negative block determines if the input is less than zero, and its previous value was greater than or equal to zero.

• The output is true (equal to 1) when the input signal is less than zero, and its previous value was greater than or equal to zero.

• The output is false (equal to 0) when the input signal is greater than or equal to zero, or if the input signal is negative, its previous value was also negative.

Data Type Support

The Detect Fall Negative block accepts signals of the following data types:

• Floating point

• Built-in integer

• Fixed point

• Boolean

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

Parameters and Dialog Box

Initial condition

Set the initial condition of the Boolean expression U/z < 0.

Input processing

Specify whether the block performs sample- or frame-based processing. You can select one of the following options:

• Elements as channels (sample based) — Treat each element of the input as a separate channel (sample-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 in the DSP System Toolbox documentation.

• Inherited — Inherit the processing mode from the input signal and delay the input accordingly. You can identify whether the input signal is sample or frame based by looking at the signal line. Simulink represents sample-based signals with a single line and frame-based signals with a double line.

  Note   When you choose the Inherited option for the Input processing parameter, and the input signal is frame-based, Simulink® will generate a warning or error in future releases.

Use Input processing to specify whether the block performs sample- or frame-based processing. The block accepts frame-based signals for the input u. All other input signals must be sample based.

Input Signal u	Input Processing Mode	Block Works?
Sample based	Sample based	Yes
Frame based		No, produces an error
Sample based	Frame based	Yes
Frame based		Yes
Sample based	Inherited	Yes
Frame based		Yes

For more information about these two processing modes, see Sample- and Frame-Based Concepts in the DSP System Toolbox documentation.

Output data type

Set the output data type to uint8 or boolean.

Characteristics

Direct Feedthrough	Yes
Scalar Expansion	Yes

See Also

Detect Change, Detect Decrease, Detect Fall Nonpositive, Detect Increase, Detect Rise Nonnegative, Detect Rise Positive

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