Group Signal Lines into Virtual Buses

You can combine signals into a bus and then access the bus as a whole or select specific signals from the bus. A virtual Simulink^® bus is analogous to a bundle of wires held together by tie wraps. For comparison, a nonvirtual Simulink bus is analogous to a struct in C code.

Not all blocks can accept buses and some blocks implicitly convert buses to vectors. To learn which blocks support which types of buses, see Bus-Capable Blocks. To identify bus conversions, see Manage Bus-to-Vector Conversions.

How you create virtual buses differs based on the location of the signals that you want to group.

To focus on fundamental steps, these examples are simple, however, buses are most useful when you have many signals to combine.

Tip

When you create a bus, the line style updates when you simulate the model or, on the Modeling tab, click Update Model.

Group Signal Lines Within a Component

Open Model

This example shows how to group signals into a virtual bus using Bus Creator blocks.

Open the example model, which contains three blocks.

To create a bus that contains the signals from multiple blocks, drag to select the blocks. For this example, select the Chirp Signal and Sine Wave blocks. In the action bar that appears, click Create Bus.

Simulink adds a Bus Creator block and connects the input signals to that block. The output of the Bus Creator block is a virtual bus.

To make it easier to identify the elements of the bus, label the input signals to the Bus Creator block. Label the output signal of the Chirp Signal block by double-clicking the signal line and entering Chirp. Similarly, label the output signal of the Sine Wave block Sine.

To create a second bus that contains the first bus and the output signal of the Step block, drag to select the Bus Creator and Step blocks. In the action bar that appears, click Create Bus. Since the Sine and Chirp signals are elements of the input bus, Simulink creates the same bus regardless of whether your selection includes the Sine Wave and Chirp Signal blocks.

Simulink adds another Bus Creator block and connects the input signals to that block. Label the output signal of the Step block Step and the output signal of the first Bus Creator block NestedBus. You can nest buses to any depth. If one of the inputs to a Bus Creator block is a bus, then its output is a bus hierarchy that contains at least one nested bus.

Connect the output signal of the second Bus Creator block to an Outport block and label the signal TopBus. Now that all signal lines are connected, simulate the model.

Connect Multiple Output Signals to a Port

Open Model

This example shows how to combine the output signals of a subsystem or model into a virtual bus using Out Bus Element blocks.

Open the example model, which contains a subsystem with three source blocks.

Open the subsystem and add an Out Bus Element block to it. An Out Bus Element block is similar to a Bus Creator block connected to an Outport block. Connect the output of the Chirp Signal block to the Out Bus Element block.

The label next to the Out Bus Element block has two parts. The first part of the label describes the bus (OutBus) and the second part of the label describes the bus element (signal1). To make identifying elements of the bus easier, rename the element by double-clicking signal1 and entering Chirp.

Use Ctrl+drag on the Out Bus Element block to make two copies of the block. When copying the block this way, you must specify whether to create a new port or use the existing port. To create one output bus that contains all of the signals, choose Use Existing Port each time you copy the block, then connect the signals.

To create hierarchy in the output bus, use dots in the part of the label that describes the bus element. Each dot creates a new level of hierarchy. Create a nested bus named NestedBus by defining the bus elements as NestedBus.Sine and NestedBus.Step respectively.

Inspect the hierarchy in the block parameters dialog box for the port by double-clicking on any of the Out Bus Element blocks.

Alternatively, if you grouped the Sine and Step signals into a virtual bus using a Bus Creator block, you could connect that bus to an Out Bus Element block. The label specifies the name of the element connected to the block, which is the NestedBus virtual bus.

Return to the top model. The three Out Bus Element blocks correspond with one port. Connect the output of this port to an Outport block and simulate the model.

Combine Multiple Subsystem Ports into One Port

Open Model

This example shows three ways to simplify a subsystem interface by converting multiple ports and their connected signals into one port and a bus.

Open the example model, which contains two subsystems with multiple input and output ports.

Drag a selection box around the signal lines between the two subsystems. From the action bar that appears, click Create Bus.

Simulink replaces the Inport and Outport blocks in the source and destination subsystems with In Bus Element and Out Bus Element blocks.

Drag a selection box around the signal lines between the source blocks and first subsystem. From the action bar that appears, click Create Bus.

Simulink adds a Bus Creator block before the first subsystem and replaces the Inport blocks in the first subsystem with In Bus Element blocks.

Drag a selection box around the signal lines between the second subsystem and Scope blocks. From the action bar that appears, click Create Bus.

Simulink replaces the Outport blocks in the second subsystem with Out Bus Element blocks and adds a Bus Selector block after the second subsystem.

The resulting model uses virtual buses at the subsystem interfaces.