Merge

Combine multiple signals into single signal

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Libraries:
Simulink / Signal Routing
HDL Coder / Ports & Subsystems

Description

The Merge block combines inputs into a single output. The output value at any time is equal to the most recently computed output of its driving blocks. Specify the number of inputs by setting the Number of inputs parameter.

Use a Merge block to interleave input signals that update at different times into a combined signal in which the interleaved values retain their separate identities and times. To combine signals that update at the same time into an array or matrix signal, use a Concatenate block.

Guidelines for Using the Merge Block

When you use the Merge block, follow these guidelines:

• Always use conditionally executed subsystems to drive Merge blocks, without any intervening blocks.

• Ensure that at most one of the driving conditionally executed subsystems executes at any time step.

• Ensure that all input signals have the same sample time.

• Do not branch a signal that is input to a Merge block.

• Do not log a signal that is input to a Merge block.

• Do not specify the block execution priority of a Merge block. For more information, see Specify Block Execution Order, Execution Priority and Tag.

• For all conditionally executed subsystem Outport blocks that drive Merge blocks, set Output when disabled to held.

• If the output of a Model block is coming from a MATLAB Function block or a Stateflow^® chart, do not connect that output port to the input port of the Merge block.

• The Merge block supports merging signals in different tasks to a root Outport block.

For each input of a Merge block, the topmost nonvirtual source must be a conditionally executed subsystem (not including a For Iterator or While Iterator subsystem).

The next diagram shows valid Merge block usage, merging signals from two conditionally executed subsystems.

Bus Support

The Merge block is a bus-capable block. The inputs can be virtual or nonvirtual bus signals subject to these restrictions:

• The number of inputs must be greater than one.

• Initial output must be zero, a nonzero scalar, or a finite numeric structure.

• The Allow unequal port widths check box must be cleared.

• All inputs must be buses and must be equivalent (same hierarchy with identical names and attributes for all elements).

All signals in a nonvirtual bus input to a Merge block must have the same sample time. You can use a Rate Transition block to change the sample time of an individual signal, or of all signals in a bus.

Merging S-Function Outputs

The Merge block can merge a signal from an S-Function block only if the memory used to store the output from the S-Function block is reusable. Simulink^® displays an error message if you attempt to update or simulate a model that connects a nonreusable port of an S-Function block to a Merge block. See ssSetOutputPortOptimOpts.

Multi-tasked Root Outputs

A Merge block connected to a root Outport block allows merging signals in different tasks by allowing those signals to write to the root Outport block simultaneously. A Union sample time of the sources is assigned to the Merge block.

All the sources of the Merge block that are in the same task should be inside conditionally executed subsystems that should not output simultaneously in the same time step.

Examples

Merge Block with Input from Atomic Subsystems

This example shows a Merge block with inputs from two atomic subsystems.

Each Atomic Subsystem block contains an enabled subsystem. This satisfies the requirement that inputs to a Merge block are from a conditionally executed subsystem.

Merge Block with Unequal Input Widths Example

This example shows how to use the Merge block with inputs ports that have different widths. If you select Allow unequal port widths, the block accepts scalar and vector inputs having differing numbers of elements. You can specify an offset for each input signal relative to the beginning of the output signal. The width of the output signal is:

where are the widths of the input signals, and are the offsets.

The Merge block has the following output width.

In this example, the offset of is 0 and the offset of is 1. The Merge block maps the elements of to the first two elements of and the elements of to the last two elements of . Only the second element of is effectively merged, as show in the scope output.

If you use Simplified Initialization Mode, you must clear the Allow unequal port widths check box. The input port offsets for all signals must be zero.

Extended Examples

Merging Signals

Use conditionally executed subsystems and the Merge block to combine two inputs into a single output.

• Open Model

Limitations

• All signals that connect to a Merge block are functionally the same signal. Therefore, they are subject to the restriction that a given signal can have at most one associated signal object. See Simulink.Signal for more information.

• Run-time diagnostics do not run if the inputs to a Merge block are from a single initiator. For example, a single initiator could be a Stateflow chart executing function-call subsystems that are connected to a Merge block.

• Do not set the outports of conditionally executed subsystems being merged to reset when disabled. This action can cause multiple subsystems to update the block at the same time. Specifically, the disabled subsystem updates the Merge block by resetting its output, while the enabled subsystem updates the block by computing its output.

  To prevent this behavior, set the Outport block parameter Output when disabled to held for each conditionally executed subsystem being merged.

• A Merge block does not accept input signals whose elements have been reordered or partially selected, as shown in the next diagram.

  

• Do not connect input signals to the block that have been combined outside of a conditionally executed subsystem.

You can use an array of buses as an input signal to a Merge block with these limitations:

• Allow unequal port widths — Clear this parameter.

• Initial condition — You can specify this parameter using:

  • The value 0. In this case, each of the individual signals in the array of buses use the initial value 0.

  • An array of structures that specifies an initial condition for each of the individual signals in the array of buses.

  • A scalar structure that specifies an initial condition for each of the elements that the bus type defines. Use this technique to specify the same initial conditions for each of the buses in the array.

Ports

Input

Port_1 — First input signal

scalar | vector

First input signal merged with the other input signals.

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

Port_n — nth input signal

scalar | vector

nth input signal merged with the other input signals.

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

Output

Port_1 — Output signal

scalar | vector

Output signal merged from the input signals.

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

Parameters

Number of inputs — Number of input signals to merge

2 (default) | integer

Specify the number of input signals to merge. The block creates a port for each input signal.

Programmatic Use

Block Parameter: Inputs

Type: character vector

Values: integer

Default: '2'

Initial output — Initial output value

[ ] (default) | scalar | vector

Specify the initial value of the output signal. If you do not specify an initial output value, then initial output depends on the initialization mode and the driving blocks.

In Simplified Initialization Mode, for an unspecified (empty matrix []) value of Initial output, the block uses the default initial value of the output data type. For information on the default initial value, see Initialize Signal Values. In Classic Initialization Mode, for an unspecified (empty matrix []) value of Initial output, the initial output of the block equals the most recently evaluated initial output of the driving blocks. Since the initialization ordering for these sources can vary, initialization can be inconsistent for the simulation and the code generation of a model.

Programmatic Use

Block Parameter: InitialOutput

Type: character vector

Values: scalar | vector

Default: '[ ]'

Allow unequal port widths — Allow inputs of unequal dimensions

off (default) | on

Select this parameter to allow the block to accept inputs having different numbers of elements from each other or from the output. The block allows you to specify an offset for each input signal relative to the beginning of the output signal. The width of the output signal is

max(w1+o1, w2+o2, ... wn+on)

where w1, ... wn are the widths of the input signals and o1, ... on are the offsets for the input signals.

If you clear this parameter, the Merge block accepts only inputs of equal dimensions and outputs a signal of the same dimensions as the inputs.

Note

Do not select this parameter unless your model is using Classic Initialization Mode.

Programmatic Use

Block Parameter: AllowUnequalInputPortWidths

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Input port offsets — Offset for input signals

[ ] (default) | vector

Enter a vector to specify the offset of each input signal relative to the beginning of the output signal.

Dependencies

To enable this parameter, select Allow unequal port widths.

Programmatic Use

Block Parameter: InputPortOffsets

Type: character vector

Values: scalar | vector

Default: '[ ]'

Block Characteristics

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

Extended Capabilities

C/C++ Code Generation

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

In the code generation workflow, when the Merge block receives a constant value and non-constant sample times, one of these conditions must hold. Otherwise Simulink displays an error.

• The source of the constant value is a grounded signal.

• The source of the constant value is a constant block with a non-tunable parameter.

  • There is only one constant block that feeds the Merge block.

  • All other input signals to the Merge block are from conditionally executed subsystems.

  • The Merge block and outport blocks of all conditionally executed subsystems does not specify any initial outputs.

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 within your design. Distributed pipelining does not redistribute these registers. The default 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 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).

PLC Code Generation

Generate Structured Text code using Simulink® PLC Coder™.

Code generation not supported when this block is used inside a For Each Subsystem block.

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

Version History

Introduced before R2006a