Altium NEXUS Documentation

Creating Circuit Connectivity in Your Schematics in Altium NEXUS

Created: December 17, 2020 | Updated: September 15, 2021
Now reading version 4. For the latest, read: Creating Circuit Connectivity in Your Schematics for version 5
This documentation page references Altium NEXUS/NEXUS Client (part of the deployed NEXUS solution), which has been discontinued. All your PCB design, data management and collaboration needs can now be delivered by Altium Designer (with Altium Designer Enterprise Subscription) and a connected Altium 365 Workspace. Check out the FAQs page for more information.

Parent page: More about Schematics

It is the components and how they connect to each other that create your unique, electronic circuit. In the schematic, you create the logical representation of your design by connecting the component pins together; to design the printed circuit board, you place the physical components and create the same connectivity with the routing.

If you're learning how to structure your design and create connectivity, you might find the following pages helpful.

Learn about Compiling and Verifying the Design

Learn about Multi-Sheet and Multi-Channel Design

Learn about Design Synchronization

Physical and Logical Connectivity

On the schematic, you can create that connectivity by drawing a wire from one component to another - this is referred to as physical connectivity.

You can also connect one pin to another by placing a short Wire and a Net Label on each component pin. The software identifies these two net sections and connects them to form a single net. This type of connectivity is referred to as logical connectivity.

Physical connectivity allows a user to follow each wire as they study the circuit, but a lot of wires can result in a dense and busy schematic. On the other hand, Net Labels reduce the amount of wiring, but the user must scan the sheet to find all potential connections. As the designer, you are free to decide which connectivity model best suits your design, including a mixture of both techniques.

Animated image showing the difference between physical connectivity and logical connectivity

Place wires to create physical connectivity or use net labels to create logical connectivity.

As well as creating logical connectivity within a schematic sheet, there are also objects for creating logical connectivity between schematic sheets. The way this connectivity is created will depend on how you structure your schematic: either as a flat design or as a hierarchical design. More about this below.

Sheet-to-sheet connectivity can be created by a number of different objects, called Net Identifiers
There are a number of different net identifiers that can be used to connect between sheets.

Connectivity Insight 

The Altium NEXUS Connectivity Insight functionality (part of the Design Insight feature) displays an instant view of the connection relationships within a project. Shown as a document tree with optional schematic previews, the selectable elements provide a quick and visual way to navigate through a project's connectivity structure.

In its default setup condition, the Connectivity Insight feature displays:

  • The related net connection information when the cursor hovers over a schematic connectivity object (wire, port, etc.).
  • A tree-based connectivity preview map when ALT+Double-click is used on the object.

Adding to this capability is a feature that is accessed by hovering over an object that belongs to a signal net then pressing Ctrl+Alt. This opens a selectable tree view. Click the desired sheet in the tree to quickly jump to that document. 

This feature can be enabled/disabled on the System - Design Insight page of the Preferences dialog by checking/unchecking the Mouse Hover option for the Document Tree entry.

Objects Used to Create Connectivity

The schematic editor includes the following objects that are used to create connectivity. Collectively these objects are referred to as net identifiers.

Net Identifier Function
Bus Used to bundle a set of nets, for example, Data[0..7]. Nets must be named sequentially using a specific naming scheme (e.g., Data0, Data1,... Data7). This naming then dictates the Bus name, for example, Data[0..7].
Bus Entry Graphical device provided to support ripping two different nets from opposite sides of a bus line without creating a short between the two nets. Not required in other situations.
OffSheet Connector Used to connect a net from one schematic sheet to another sheet (not within the same sheet). Only supports horizontal connectivity (flat designs). OffSheet Connectors have limited functionality when compared to Ports.
Net Label A net identifier used to create connectivity to other Net Labels with the same name on the same schematic sheet. The net is automatically named by the Net Label. Net Labels can be placed on component pins, wires and buses. Note that Net Labels do not connect between sheets unless the project options are configured to use a Net Identifier Scope of Global.
Pin Pins are placed in the schematic symbol editor to represent the physical pins on the component. Only one end of the pin is electrically active, which is sometimes referred to as the hot end of the pin.
Port Used to connect a net from one schematic sheet to another. Connectivity can be vertical in a hierarchical design, or horizontal in a flat design (vertical and horizontal designs are explained below). Port names are used to name nets if the Allow Ports to Name Nets option is enabled in the Options tab of the Project Options dialog. in this situation, Ports will also connect within a schematic sheet.
Power Port Creates connectivity to every other power port of the same name, throughout the schematic project, regardless of the design structure. The net is automatically named by the Power Port. This net can be localized to a specific schematic sheet if required.
Sheet Entry Placed within a Sheet Symbol, to create connectivity to a Port of the same name on that Sheet Symbol's child sheet. Sheet Entries are used as net names if the Allow Sheet Entries to Name Nets option is enabled in the Options tab of the Project Options dialog.
Signal Harness Used to bundle any combination of nets, buses and lower-level signal harnesses.
Wire A polyline electrical design primitive that is used to form electrical connections between points on a schematic. A Wire is analogous to a physical wire.

Different types of net identifiers that have the same name do not automatically connect to each other. It depends on how the net naming options are configured. These options are discussed below.

How The Design Structure Affects the Connectivity

Related article: Multi-sheet and Multi-channel Design

If the design does not fit onto a single schematic sheet, it can be spread over multiple sheets. There are two distinct models for organizing and creating connectivity in a multi-sheet schematic: either as a flat design, which you can think of as one large schematic sheet that has been cut up into a number of smaller sheets; or as a hierarchical design, where the sheets are linked in a grandparent-parent-child type structure.

Multi-sheet designs are implemented by placing a Sheet Symbol on the parent sheet, which represents and links to the child sheet, as shown in the image below.

Image showing how multiple sheets can be connected through a parent sheets, using sheet symbols
Sheet Symbols represent (and link to) lower-level sheets. In a flat design, this structure can only be one level deep; in a hierarchical design, there is no limit to the depth.

So just what determines if a design is flat or hierarchical? This is done by setting the Net Identifier Scope to define how you want the sheet-to-sheet connectivity to be created. Set this in the Options tab of the Project Options dialog.

It is important to remember that for hierarchical designs, a project can contain only one top sheet. All other source documents must be referenced by sheet symbols. When performing a design validation, the Multiple Top Level Documents violation check can be used to flag if this is not the case. In addition, no sheet symbol may reference the sheet it's on or any sheet higher up the ladder, as this will create an irresolvable loop in the structure.

Flat Design

Related article: Multi-sheet and Multi-channel Design

A design is referred to as a flat design when the connectivity is created directly from one sheet to another sheet. It does not pass through Sheet Symbols on the parent sheet. In a flat design, the sheet symbols simply represent (and reference) the child sheets. All sheets in the design appear at the same level in the Projects panel because there is no hierarchy. Both of the images below show a flat design.

Flat designs are simpler to create. A flat design can include a top sheet with a Sheet Symbol for each child sheet, but this is optional since this top sheet is not used to create sheet-to-sheet connectivity. For a small design that only has two or three schematic sheets in it, you might decide that a top sheet does not add any value. Once the sheet count gets higher, a top sheet can help the reader understand the functionality of the circuit design from the way that the logical blocks (Sheet Symbols) are arranged on the sheet.

Projects panel showing a simple project that is a flat design, without a top sheet  Projects panel showing a simple project that is a flat design, with a top sheet
The same design, shown without a top sheet (left) and with a top sheet (right) - both are examples of a flat design.

In a flat design, the connections between the sheets can be created by Ports, Offsheet Connectors, Power Ports, and Net Labels, as shown in the image above with the magnifying glass. The recommended approach is to use Net Labels within each sheet and Ports to connect between sheets. Ports offer more features than Off-Sheet Connectors, including the ability to add Port Cross References, which adds a SheetName[GridReference] to each port, referring to a matching port on another sheet, as shown in the image below.

There is no limit to the number of sheets in a flat design.

Ports can be used to create sheet-to-sheet connections, and Port Cross References can be added, if required
Port Cross References have been added next to each Port indicating the target sheet and grid reference for the matching Port.

A design is flat when the connectivity is directly from one sheet to another. This connective behavior is defined by setting the Net Identifier Scope to Automatic, Flat or Global. Note that if you choose to use a mixture of Ports and Net Labels to create sheet-to-sheet connectivity, you cannot use the Automatic option. In this situation, you must manually set the Net Identifier Scope to Global.

Hierarchical Design

Main article: Multi-sheet and Multi-channel Design

A design is referred to as hierarchical when the sheet-to-sheet connectivity is from a Sheet Symbol down to the child sheet referenced by that Sheet Symbol. At the net level, the connectivity is created between a Sheet Entry in that Sheet Symbol and a Port with the same name as the sheet entry on the child sheet. This type of connectivity is also referred to as vertical connectivity since the sheet-to-sheet connectivity that is created is only up and down between a parent sheet and its child sheet.

In a hierarchical design connectivity is between a port on the child sheet and a matching sheet entry on the parent sheet
In a hierarchical design, the net-level connectivity is from a Sheet Entry on the parent sheet down to a matching Port on the child sheet.

Hierarchical designs have two major strengths.

  1. The first is the ability to show the reader the functionality of the design in the way that the schematic sheets have been structured and presented as logical blocks (Sheet Symbols). The top-level schematic presents the design as a set of high-level functional blocks with the arrangement of the blocks reflecting their place in the traditional left-to-right, input-to-output flow of the overall circuit. These blocks can be further broken down into smaller blocks. if required, allowing the lowest level schematics that carry the components to have a relatively simple structure with a low component count. Because each sheet is relatively simple, the measured sheet size can be kept small, which is a big advantage when it comes to printing the schematic.
  1. The other major advantage is that it is generally much easier to trace a signal through a hierarchical design since the reader only needs to match a Sheet Entry on the parent sheet to the Port on the child sheet, and can trace the signal along the wiring within each sheet.

There is extra work in building up a hierarchical design. The Sheet Symbols require Sheet Entries and the top sheet must be wired to carry the signals from one Sheet Symbol to another. The software includes a tool to help keep the Sheet Entries synchronized with the child-sheet Ports (Design » Synchronize Sheet Entries and Ports for all Sheet Symbols, or right-click on a Sheet Symbol then choose Sheet Symbol Actions » Synchronize Sheet Entries and Ports for a single Sheet Symbol). It also includes tools to help break down a larger design into small chunks (Edit » Refactor » Move Selected Subcircuit to Different Sheet). To learn more about these restructuring and refactoring tools, refer to the  Design Refactoring page.

A hierarchical design can be any depth and include any number of schematic sheets.

A design is hierarchical when the sheet-to-sheet connectivity is only between Sheet Entries on the parent sheet and matching Ports on the child sheet. This connective behavior is defined by setting the Net Identifier Scope to Automatic, Hierarchical or Strict Hierarchical.

Multi-channel Design

Main article: Multi-sheet and Multi-channel Design

It is not unusual for an electronic design to include repeated sections of circuitry. It might be a stereo amplifier or a 64-channel mixing desk. This type of design is fully supported by a feature set known as multi-channel design. In a multi-channel design, you capture the repeated circuit once then instruct the software to repeat it by either placing multiple Sheet Symbols that all reference the same child schematic, or by configuring a single Sheet Symbol to repeat the referenced child schematic the required number of times. The compiled design is expanded out in the computer's memory with all components and connectivity repeated the required number of times in accordance with the user-defined naming scheme.

An example of a multi-channel design where the child schematic is repeated by placing 4 instances of its Sheet Symbol  An example of a multi-channel design where the child schematic is repeated by including the Repeat keword in its Sheet Symbol
On the left, there are four Sheet Symbols all referencing the same child sheet (PortIO.SchDoc). On the right, the InputChannel.SchDoc is repeated eight times by the Repeat keyword.

The logical design that you capture is never actually flattened; it always remains as a multi-channel schematic. When you transfer it to PCB layout the physical components and nets are stepped out the required number of times, and you have full access to the cross-probing and cross-selecting tools available for Working Between the Schematic and the Board. There is also a tool in the PCB editor to replicate the placement and routing of one channel across all other channels, with the ability to easily move and reorient an entire channel. Refer to the multi-channel design document to learn more about multi-channel design. 

A multi-channel design must be hierarchical because the software uses this structural model to instantiate the channels in memory.

For a multi-channel design, set the Net Identifier Scope to Automatic, Hierarchical or Strict Hierarchical.

The duplication of components and nets is resolved by the software using the naming scheme selected on the Multi-Channel tab of the Project Options dialog.

Setting the Net Identifier Scope

Dialog page: Options for Project

The software uses the current setting of the Net Identifier Scope to work out how to establish connectivity between the schematic sheets. The Net Identifier Scope is configured in the Options tab of the Project Options dialog (Project » Project Options).

Select the Net Identifier Scope mode to suit the structure of your design.
Select the Net Identifier Scope mode to suit the structure of your design.

The behavior of the Global, Flat and Hierarchical options are shown in the images below.

Configuring the Net Identifier Scope, example of what connects with the Global option Configuring the Net Identifier Scope, example of what connects with the Flat option Configuring the Net Identifier Scope, example of what connects with the Hierarchical option
Simple examples of how connectivity is created for each of the three main modes: Global, Flat, Hierarchical.

As well as the three options mentioned above, there is also an Automatic option. Generally, it is better to leave the Net Identifier Scope set to Automatic. The software will select the most appropriate of the three options based on the structure of the sheets and the presence/lack of Ports and Sheet Entries.

When set to Automatic, the software automatically selects which of the three main net identifier modes to use based on the following criteria:

  • If there are sheet entries on the top sheet, Hierarchical is used.
  • If there are no sheet entries but there are ports present, Flat is used.
  • If there are no sheet entries and no ports, Global is used.

The Strict Hierarchical mode localizes all power ports to each sheet. In this mode, you must wire all the power and ground nets onto each child sheet using Ports and Sheet Entries. You can also do this for selective sheet(s) by not using the Strict Hierarchical mode, but still placing Sheet Entry(s) + Port(s) for the power net(s) you want to localize.

How Nets are Named

Each time you place a wire between component pins, you are creating connectivity. Every net in the design is given a name. If you have not placed a net identifier that can be used to name the net, the software names that net based on one of the pins in the net, for example, NetR7_1 as shown in the image below. If the component designator is changed at some stage, that system-generated net name is also changed and these changes must be passed between the schematic and PCB to keep everything in sync.

Image shows how nets are automatically named, if a Net Label has not been placed on the schematic
Nets without a net identifier are assigned a system-generated name based on one of the pins in the net.

Net Labels always name the net to which they are attached. The default point of attachment is the bottom left corner of the Net Label, which is indicated by a small cross during movement.

For other net identifiers, they name the net if the appropriate option is enabled in the Netlist Options section of the Options tab of the Project Options dialog.

Different types of net identifiers do not automatically connect with each other. For example, a Port called Reset will not connect to a Net Label called Reset even if the Allow Ports to Name Nets option in the Project Options dialog is enabled. They must be connected by a wire. An example is shown in the images below.


Multiple Net Identifiers on a Net

You cannot have multiple Net Labels with different names on the same net within a schematic sheet. This situation will be detected and flagged as an error during validation. However, it is legitimate to have multiple net identifiers on a net on different sheets on which the net appears.

This ability allows you to:

  • Change the name of a net at different levels in the hierarchy to better reflect its function on that sheet.
  • Reuse a child schematic sheet without needing to rename nets on it.

The default setting is to assume that multiple net identifiers are not allowed. If they are detected during validation, a warning will be given. If you require them for your design, you will need to either:

  • Change the setting of the Nets with multiple names error check on the Error Reporting tab of the Project Options dialog or,
  • Suppress specific warnings by placing a No ERC Marker on each warning then choosing Specific Violations on the No ERC mode of the Properties panel to define the errors to suppress. Note that No ERC markers can be placed by right-clicking on a warning listed in the Messages panel or by right-clicking on the wavy colored line marking a violation on the schematic sheet. Their shape and color can be changed in the Properties panel when the No ERC marker is selected.

Options for Controlling the Naming of the Nets

Dialog page: Project Options

Ultimately, each net can have only one name on the PCB (one PCB net cannot have two names unless you are intentionally connecting two nets with a Net Tie). The software automatically resolves nets with multiple names to have only a single name in the project, but it may not be the name you expect. There are a number of options available to control how the name is chosen in the Netlist Options section of the Options tab of the Project Options dialog. Refer to the Project Options dialog page for more details about each of the options.

A good approach to setting these options is to enable the Allow Ports to Name Nets and the Higher Level Names Take Priority options. Combine these with sensible usage of Net Labels on significant nets on each sheet to ensure that all of the important nets, including those that traverse sheets, are named, and that the names assigned on the higher-level schematics are used on the lower-level schematics.

When there are multiple net naming options enabled, the precedence for naming nets is as follows:

  • If the Power Port Names Take Priority option is off, the order is Net Labels, Power Ports, Ports, Pins.
  • If the Power Port Names Take Priority option is on, the order is Power Ports, Net Labels, Ports, Pins.

Two Separate Nets That Have the Same Name

Another net naming issue that can arise is when the same net name has been used on different schematic sheets to label different nets. This will be detected during validation by the Duplicate Nets error check. You cannot transfer a design to the PCB with this condition present. Those two separate nets will be merged into a single PCB net during design transfer.

This situation can be resolved by enabling the Append Sheet Numbers to Local Nets option on the Options tab of the Project Options dialog. With this option enabled, all local nets have the value of the SheetNumber parameter appended to their name, as shown in the images below.

Example of how a duplicated net name, Input, appears on the schematic Editor tab  Example of how a duplicated net name, Input, appears on the schematic compiled tab
Since the net label Input has been used on multiple sheets, the Append Sheet Numbers to Local Net option has been enabled to prevent a Duplicate Nets error.
The effect of this can be seen by clicking on the complied sheet tab (right image), note that _2 has been appended to the net name.

The Append Sheet Numbers to Local Nets option will work only if each schematic sheet has been assigned a unique SheetNumber. The SheetNumber parameter is assigned on the Parameters tab of the Document Options mode of the Properties panel for each schematic sheet. As an alternative to manually assigning a unique number to each schematic sheet, run the Tools » Annotation » Number Schematic Sheets command, which opens the Sheet Numbering for Project dialog. This dialog can be used to assign unique SheetNumbers (a simple numeric value for each sheet) and DocumentNumbers (typically used for company-assigned document numbering) to all sheets.  

Intentionally Connecting Two Nets

There are situations when you need to intentionally connect two different nets. This is not a simple naming issue. It is when two nets need to be shorted as a design requirement. An example could be when you need to connect an Analog ground and a Digital ground in a controlled way.

This is achieved by connecting the two nets through a Net Tie component. A Net Tie component is nothing more than a controlled short circuit, allowing you to decide the location on the board where the nets connect. On the schematic, the Net Tie component has two or more pins, with each pin connected to one of the nets to be shorted. The Component Type property of the component is set to Net Tie, as shown below.

A Net Tie component being used to route a single clock to two FPGA clock pins on the schematic.
A Net Tie component being used to route a single clock to two FPGA clock pins on the schematic.

Note that the pins are not wired to each other on the schematic (they are not shorted on the schematic), but they are connected together within the PCB footprint.

On the PCB side, the footprint has the same number of pads as the schematic symbol has pins with copper between them. In the example image below, this is achieved by connecting two square pads with a length of track. This is done within the footprint in the PCB library editor. The PCB Component Type property is also set to Net Tie.

The software automatically ignores short circuits created within a Net Tie PCB component, therefore, a DRC error is not created.

A Net Tie (component type) is also used to intentionally connect 2 nets on the PCB
The same Net Tie component on the PCB; the pads (selected) in the Net Tie footprint are shorted with a track.

When a Net Tie component is used to connect two different nets, each net retains its own name throughout the schematic and on the PCB.

  • When creating the Net Tie symbol and footprint, there are two Net Tie Component Type modes: one to include the Net Tie in the BOM (for example, if the Net Tie is a shorting jumper), the other to exclude it from the BOM (if the Net Tie is simply a length of copper) - select the required Component Type.
  • When routing the Net Tie on the board, any of the routing modes can be used to route away from a Net Tie pad. To route into a Net Tie pad, you must switch to the Ignore Obstacle mode.

Demonstration of routing a Net Tie component

Power Nets

The default behavior of the settings is to assume that power nets are global, i.e. you want them to be available on every schematic sheet. To access a power net, place a Power Port with the required net name then wire the components to that power port.

An example showing how it is the Net property of the Power Port that determines what net it connects to, not the Style
It's the net name that determines to which net a power port is connected, not the Style of the symbol - the three highlighted power ports all connect to the GND power net.

Localizing a Power Net - Globally

As mentioned previously, power nets can be localized to each schematic sheet in a hierarchical design by selecting the Strict Hierarchical option for the Net Identifier Scope. This approach localizes all power nets on every sheet, so they must be manually wired together, using the same approach as signal nets. If they are not wired together, there will be a Duplicate Net Name error for each power net present on each schematic sheet. You will also need to adjust the Connection Matrix settings to allow Ports to be connected to Power Ports.

Power Ports can be restricted to each sheet by enabling the Strict Hierarchical mode, but must then be manually wired
If the Net Identifier Scope is set to Strict Hierarchicalevery power net must be wired to every sheet on which they are used.

Localizing a Power Net - Individually

A specific power net can also be localized on a specific sheet by wiring the Power Port to a Port on that schematic sheet.

An individual power net can be localized to a sheet by connecting it to a Port on that sheet
Here the 3V3 power net has been localized for just this sheet, so it must also be manually wired on the parent sheet. The GND and 5V nets remain as global power nets.

Power Nets and Hidden Power Pins

Older versions of Altium's design software included features and options to support the use of hidden schematic component pins. This feature was useful when a design had a single power net and a single ground net, allowing all the power pins on all devices to be automatically connected to their respective nets by hiding those power pins. It was most popular on multi-part components, freeing you from having to display the power pins for these components on the schematic.  

Today, electronic designs typically have multiple power and ground nets. These nets are not simply routed to the relevant power pins; power delivery is now a critical aspect of successful board design. 

As the nature of designing power delivery networks has changed, the need to be able to hide component pins and have the software automatically connect them has dropped off to the point where most designers oppose this practice. Because of this, the software no longer supports defining a pin as hidden and pre-assigning its net name. Older projects that use this design approach will still netlist correctly when they are opened in the latest version of Altium's design software.

Bundling Multiple Nets

A common challenge in a large design is keeping the nets manageable. Not only from the perspective of the designer creating the connectivity but also from the perspective of the reader that has to interpret and understand the schematic. This is particularly important when connecting between sheets as this is when both the designer and the reader can most easily get confused.

This can be helped by bundling nets into Buses or Signal Harnesses.

Working with Buses

Buses are used to bundle a series of sequential nets, for example, an address bus or a data bus. Their core requirement is that each net in the bus is named with a common base name, followed by a numeric identifier, as shown in the images below. For example, the nets Control1, Control2 and Control3 can be bundled into the bus Control[1..3]. Buses cannot be used to bundle an unrelated set of nets, such as the nets Enable, Read and Status, Signal Harnesses are used to do this, as explained below.

To create a valid bus, it must include all of these elements (as shown in the images below):

  • A Net Label on each of the individual nets
  • A Net Label on the Bus line
  • A Port named the same as the Bus if it is leaving this sheet

An example of how multiple nets can be bundled into a Bus  An example of how multiple nets can be bundled into a Bus, this time Bus Entries have been used to rip nets from both sides
All of the elements shown in the image above must be included to create a valid Bus. Bus Entries only need to be used if you want to rip different bus elements from both sides of the Bus.

Buses are not transferred to the PCB, instead, a Net Class can be created for each schematic Bus, or if required, for each Bus section. A bus section is created by specifying a bus which is actually a section of a larger bus, for example, from the bus D[15..0]. If this option is enabled then the PCB will include a Net Class for the entire bus, as well as each section that has been defined. Enable the required options in the Class Generation tab of the Options for Project dialog.

Working with Signal Harnesses

Signal harnesses are highly flexible as they can be used to bundle any number of nets, buses and lower-level harnesses. As their name implies, they are analogous to a wiring harness, where any arrangement of wires can be bundled and routed through an electronic or electrical product. They are more complex to create and manage, but the reward is that they can greatly simplify the presentation of a schematic and enhance its readability.

Image showing the various elements used to create a Signal Harness
Signal harnesses are used to bundle any combination of nets, buses, and lower-level signal harnesses.

The elements that make up a complete signal harness include:

  • Harness Connector - Think of a Harness Connector as a funnel, it gathers all of the signals that connect into this harness through the included Harness Entries. A key property of the Harness Connector is the Harness Type, this identifies the harness and is used to bind together the various elements that make up the signal harness, including the connected Ports / Sheet Entries.
  • Harness Entries - Each signal (net, bus or signal harness) that you want to be part of this signal harness, enters the Harness Connector through a Harness Entry. The Harness Entry includes a Harness Type property, this is only used when you are nesting signal harnesses - signifying that this Harness Entry has a lower-level signal harness connected to it.
  • Signal Harness line - The bus-like line that is placed to carry the signal harness across the sheet.
  • Harness Type - A Harness Type is a set of Harness Entries. Each detected Harness Type is defined in a Harness Definition File, as described below. The Harness Type and its associated Harness Entries are essentially names of the containers that carry the nets, not the names of the nets themselves. To check the Harness Type value, hover the cursor over the object, for example, the Port, Sheet Entry, or Harness Connector. 
  • Harness Definition File - The software manages signal harnesses by recording the Harness Entries that are in each signal harness (Harness Type), in an ASCII Harness Definition File. The image below shows the syntax of a Harness Definition File, there is a line in the file for each Harness Type, which details the Harness Entries within that harness. A Harness Definition File is automatically created (and managed) for each schematic sheet that has Harness Connectors on it, you can find them in the \Settings folder in the project tree, as shown in the image below. If your design has had changes that impact the signal harnesses, the Harness Definition files are updated automatically. If a Harness Definition File is not present in the project folder, it is automatically re-created when the schematic sheet is opened (they can be deleted and will be automatically recreated if required).
  • Port + Sheet Entry - Like a Net or Bus, a Signal Harness can leave a sheet via a Port, and then connect to the higher level sheet through a matching Sheet Entry. Note that the software automatically changes the color of the Ports and Sheet Entries to show they are carrying a Signal Harness if the Sheet Entries and Ports use Harness Color option is enabled in the Schematic - Graphical Editing page of the Preferences dialog. Note also that the Port and Sheet Entry objects include a Harness Type property, this value is set automatically as you touch the Port to the Signal Harness line when you are placing the Port. For the Port on the schematic sheet where the Harness is defined (the Harness Connector is present) the Harness Type is automatically defined and is not editable. For a Port or Sheet Entry placed on a higher-level schematic sheet, it will be blank and editable, typically there is no need to manually set this. The assigned Harness Type can be checked at any time by hovering the cursor over the Port/Sheet Entry.

A schematic with two Signal Harnesses on it, above the Harness Definition text file that those two Harnesses are defined in
Harnesses definitions are stored in Harness Definition files, in the image above there are two signal harnesses defined: 1WB_Write_Read and JTAG.

As mentioned, as well as a net or a bus, you can also wire a signal harness into a signal harness, creating what is referred to as nested signal harnesses. This situation is identified at the Harness Entry, which has its Harness Type property set to the value of the incoming signal harness.

Image showing how a Signal Harness can carry other Signal Harnesses within it
As well as nets and buses, a signal harness can carry other signal harnesses.

In the previous image, the Stereo signal harness has been used twice. This is legitimate, as neither the signal harness nor the harness entries are used to identify the nets which that harness carries. You can re-use a signal harness anywhere in the design, use the Place » Harness » Predefined Harness Connector command to do this. The dialog includes options to include a Signal Harness line and a Port if required.

Place Predefined Harness Connector dialog, use this to quickly place an existing Signal Harness
Existing signal harnesses can be re-used anywhere in the design, including on the same sheet to carry different nets.

The elements that make up a signal harness are used by the design compiler to identify the nets that belong in that signal harness so that the individual logical connections carried between sheets can be resolved. Signal harness elements are not used to name the nets, this is done using the standard net naming methods already discussed.

This behavior can be overridden if required. The nets within a signal harness can be given a harness-level name, by placing a Net Label on the Signal Harness line. If this is done, then the original Net Label is no longer used, instead, the net is named based on the Net Label placed on the Signal Harness line + the Harness Entry, in the form:

  • System-defined net name = NetNameOnSignalHarness.HarnessEntryName

Image showing how to apply harness-level names to the contained nets
The JTAG signal harnesses have harness-level names defined by the presence of the Net Labels SOFT and HARD. The system-generated net names are shown in the image below.
The 1WD_Write_Read signal harness does not have a harness-level name, so its nets will retain the names from the Net Labels.

In the image above, each instance of the JTAG harness has a Net Label placed on the Signal Harness line, namely HARD and SOFT. Because this harness-level net name has been added, the net labels on the nets within these harnesses are just used to create the local connections within this sheet. The nets are automatically assigned a name using the naming syntax shown above, as can be seen in the image of the Navigator panel, below. 

Image showing how check harness-level names in the Navigator panel
Note the naming of the JTAG nets, derived from the harness Net Label and the Harness Entries.

PCB Net Classes can also be created for named signal harnesses, enable the option in the option in the Class Generation tab of the Project Options dialog. Net classes are only created for signal harnesses that are named by a Net Label.

An advantage of naming the nets in a signal harness by placing a Net Label on the Signal Harness line (as described in the previous section), is that it also allows you to work with signal harnesses without needing to include a Harness Connector and Harness Entries on the schematic sheet. Some designers prefer this approach as it results in a cleaner and simpler schematic, as shown in the image below, where the JTAG signal harness does not use a Harness Connector.

Note that this technique requires there to be at least one Harness Connector of that Harness Type somewhere in the design, or alternatively, the harness definition must be LOCKED in the Harness Definition file. This keyword prevents the software from removing it when the Harness Definition files are automatically updated. The syntax for locking a definition is shown in the image below.

Harness-level naming allows the designer to leave out the Harness Connector, but the Harness Definition must be Locked
Like signal harnesses that use Harness Connectors, a connector-free signal harness must be declared in one of the Harness Definition files for a schematic that it is used on.
Its declaration must include the LOCKED keyword, to ensure the software does not remove it or modify it.

Dynamic Compilation 

Related article: Compiling and Verifying the Design

When you connect two pins with a wire, you are drafting your design intentions, not creating an actual net. The net is not created until the project is compiled. As well as extracting details about the components and how they are connected, compiling also extracts detailed component and design parametric information. The compiled model of the project is referred to as the Unified Data Model.

In versions of the software prior to Altium NEXUS 20.0, the project had to be manually compiled to build the Unified Data Model. Since then, the design data model is incrementally updated after each user operation through dynamic compilation - creating what is referred to as the Dynamic Data Model (DDM). There is no manual compilation of the project involved, it is all done automatically. The design connectivity model is incrementally updated after each user operation, courtesy of dynamic compilation. For a design project, the automatic compilation process performs three functions: 

  1. Instantiates the design hierarchy.
  2. Establishes net connectivity between all the design sheets.
  3. Builds an internal Dynamic Data Model (DDM) of the design.

This ensures that any design changes that are made are immediately reflected in the Navigator and Projects panel.

In order to check for logical, electrical, and drafting errors between the DDM and compiler settings, you must validate the project. This command is accessed by choosing the Project » Validate Project command from the main menus or by right-clicking over the entry for a project in the Projects panel, and choosing the Validate Project command from the context menu.  

Any violations that are detected by the Compiler will be listed as warnings and/or errors in the Messages panel. The Compiler uses the options defined on the Error Reporting and  Connection Matrix tabs of the Project Options dialog (as applicable to the project type), when checking the source documents for violations.

The Dynamic Data Model

A fundamental element of the software is the Dynamic Data Model (DDM). With dynamic compilation, a single, cohesive model is created, which sits central to the design process. Data within the model can then be accessed and manipulated using the various editors and services within the software. Rather than using a separate data store for each of the various design domains, the DDM is structured to accommodate all information from all aspects of the design, including the components and their connectivity.

Concept image showing how compiling the project creates the Unified Data Model, giving each editor access to design data
The Dynamic Data Model makes all of the design data available to all of the editors and helps deliver sophisticated features like multi-channel design.

So how do you interact with the dynamic data model, for example, to trace a net through the design? You do that through the Navigator panel.

Examining the Connectivity

Reference article: Navigator panel

If the design is large and spread over many sheets, it can become difficult to follow and verify the connectivity in the design. To help with this, the Navigator panel is used. The panel gives a view of the entire, compiled design. 

The basic approach to using the panel is to:

  • Set the browsing behavior by clicking the Ellipsis button on the Navigator panel, click to configure the navigation preferences button at the top of the panel to open the Preferences dialog and enable your preferred Highlight Methods. Alternatively, right-click on the object of interest in the panel, and use the menu options to configure the navigation behavior, as shown in the image below.
  • Set the scope of your browsing in the Documents for region of the panel to browse the entire design select Flattened Hierarchy.
  • Click on a component in the Instance section of the list to jump to that component.
  • Click on a net or bus in the Net /Bus section to jump to that net or bus.
  • Hold the Alt key as you click to jump to that object on both the schematic and the PCB.

The Navigator panel is used to examine the connectivity in the design, or to find a net, component or pin
Click on a component or net in the Navigator panel to locate that component or net, and trace the connectivity through the design. Right-click to access display options.
Hover the cursor over the image to show navigating to a component on the schematic and the PCB simultaneously (hold Alt as you click in the Navigator panel to include the PCB object).

As well as locating components on the schematic and the PCB (if Alt is held) from the Navigator panel, you can also navigate pins/components/nets/buses/harnesses on the PCB, directly from the schematic.

For example, as you click to locate a component on the schematic, you can also locate that same component on the PCB.

To do this:

  • Enable the Selecting option in the Highlight Methods, and also your preferred options in the Cross Select Mode section in the System - Navigation page of the Preferences dialog.
  • Enable Cross Selection (Tools » Cross Select Mode) in both the schematic and PCB editors.

Cross Selection options are configured in the System - Navigation page of the Preferences dialog
These options configure the navigation and cross selection behavior.

Now as you select pins/components/nets/buses/harnesses on the schematic, those objects will also be selected on the PCB, as shown in the image below.

Example of selecting components and nets on the schematic, and seeing the same selected on the PCB
Selecting components and nets on the schematic, those objects are also selected on the PCB. Cross selection also works from the PCB to the schematic.

Cross Probing and Cross Selecting

As well as being able to select from one editor to the other (cross selection), the software also supports Cross Probing. Cross Probing has two modes, continuous (remain in the source editor) and jump-to (jump to the target editor). You can also cross probe from various panels and dialogs, for example, the Messages panel and the Engineering Change Order dialog. To learn more, refer to the Cross Probing and Selecting page.

Connectivity in the Board Design Space

In the PCB editor, the connectivity between the nodes in a net is represented by a series of point-to-point connection lines, which are collectively referred to as the ratsnest.

Within an individual net, the connection lines join all of the nodes in that net. The pattern, or order they connect, is called the Net Topology, which is discussed below.

The pads in the PCB net are joined by Connection Lines
The nodes in the net are connected by connection lines.

Connection lines are displayed as thin, solid lines. The connection lines are an excellent aid during component placement, to help locate and orient components that are connected to each other. To help reduce visual clutter, as you move a component all connection lines are hidden, except the connection lines connected to that component.

Animation showing how the connection lines provide visual feedback about the best location to place each component
Use the connection lines to help locate and orient the components.

As well as being a helpful guide during component placement, the connection lines are also a valuable guide during interactive routing and autorouting. Because the connectivity is monitored and updated as you work, you can route to any point on a net to complete a connection, you do not have to route up to the pad that the connection line ends on.

Net Topology

The pattern or order that the nodes in the net are connected to each other is called the net topology. Net topology is controlled by the applicable Routing Topology design rule, which defaults to a topology of Shortest. Shortest means the nodes in the net are connected to each other in a pattern that gives the shortest overall connection length for that net. This overall length is monitored as you move a component, and the pattern of the connection lines will change dynamically to keep the overall length shortest. This can be observed in the animation shown above, where the lines connecting downward from the bottom of the moving component jump as the component is being moved - this happens each time one of the connected pads moves closer to another pad in their net.

Applying a Pre-defined Topology

Reference article: Routing Topology design rule

Additional Routing Topology design rules can be created to configure a net (or net class ) to use a different topology. To demonstrate this, in the images shown below the default topology rule is shown on the left, and that same net with a new routing topology of Starburst having been applied is shown on the right. In a Starburst topology, the connections radiate from the pad with an Electrical Type of Source (the default type for all pads is Load).

The pattern that the connection lines connect all the pads in the net is called Net Topology, the default is shortest Image showing the connection lines arranged in a Starburst net topology
For the default topology, the connection lines are placed to give the shortest overall connection length. In the Starburst topology, the connection lines all radiate from a Source pad.

Applying a Custom Topology

Reference article: From-To Editor

Within an individual net, the connection between two nodes is referred to as a From-To. To control the path of the connection lines down at the individual pin-to-pin level, you can manually define From-Tos within a net, effectively creating a custom net topology. 

From-Tos are defined by setting the PCB panel to From-To Editor mode. The process of defining a From-To is to select two Nodes on Net in the panel, and click the Add From To button. To clearly identify From-Tos in the design space, they are shown as a dashed line instead of a solid line.

Image showing how an individual connection line within a net can be configured as a From-To
A From_To has been defined between 2 pads, note how the From-To line is displayed as dashed rather than solid.

When the PCB panel is in From-To Editor mode, all of the connection lines that are not From-Tos, are hidden.

For a detailed description of defining From-Tos, refer to the From-To Editor article.

Managing the Display of the Connection Lines

Reference articles: View Configuration panel, Connection object

  • Hide/show all of the connection lines by toggling the display state of the Default Connection Lines option, in the System Colors section of the Layers and Colors tab of the View Configuration panel.
  • Selectively hide/show connection lines, using the commands in View » Connections sub-menu (press the N shortcut to pop this menu up). All of the available commands have accelerator keys, making it an efficient method of performing such tasks as hiding all connection lines (N, H, A), then displaying the connection lines for a specific net (N, S, N).
  • When in single layer mode (Shift+S), display only the connection lines that connect to component pads that are on that layer. Control this using the All Connections in Single Layer Mode option in the View Configuration panel (Additional Options section of the View Options tab).
  • For a connection line whose start and end pads are on different layers, display each connection line using a combination of the start and end layer colors. Control this using the Use Layer Colors For Connection Drawing option in the View Configuration panel (Additional Options section of the View Options tab).
  • Assign color to the connection lines in a net, or a set of nets, to help easily identify them. This is discussed below.
  • Mask or Dim all nets, except the ones you are interested in. Set the PCB panel to Nets mode, then choose either Dim (fade other objects but allow editing of faded objects) or Mask (fade other objects and only allow editing of un-faded objects) in the drop-down then click on a net (or Net Class). All objects will be faded, except those belonging to the chosen net(s), making it easy to see and work with the objects in that net.
  • While moving a component, you can temporarily disable the re-optimization and display of connection lines by pressing the N shortcut.

Component Positioning Guide

As you move a component in the design space, a thick green or red line will be displayed, traveling from a point within the component, to a location on the board. This line is called the Optimal Placement Vector, its function is to give an indication of whether the new location is better (green) or worse (red) than the previous location.

The vector has two distinct properties: its proposed target location; and its color.

To determine the locations for each end of the vector, the feature uses the centroid of the polygonal shape defined by the locations of the end points of the connection lines. There are two centroids of interest, one defined by the ends of the connection lines terminating on the component you are moving (the component centroid), the second defined by the other ends of that set of connection lines (the target location centroid).

The Optimal Placement Vector is drawn between these two centroids, with the component end highlighted by a dot. Because it is a relative indicator, when you first click to start moving a component, the vector is always drawn in green. The two centroids are continuously recalculated as you move the component because the connection lines can move from one pad to another as they are automatically re-optimized to maintain the applicable net topology for the moving component. Because of this net re-optimization, the target end of the OPV can jump around as the component is moved. If the centroids move apart and the OPV becomes longer, it may change to red. If the centroids move closer together and the OPV becomes shorter, it may change to green.

The length of the vector is not the only condition used to set the color, the color of the OPV is also affected by the overall length of the connection lines attached to the moving component. If moving the component results in the overall length of the connection lines increasing, then the OPV becomes red. Alternatively, if moving the component results in the overall length of the connection lines decreasing, then it becomes green.

Animation showing how the Optimal Placement Vector changes color to show when the connection line pattern is less optimal
Although the vector length is increasing, it remains green because the overall length of the connection lines is getting shorter.
When the component is rotated, the connection lengths increase so the OPV becomes red.

Remember that the OPV is a relative guide, each time you place the component, that new location becomes the starting point for calculations the next time you move that component.

This feature is available only when the PCB.ComponentDrag.ShowAverageHelper option is enabled in the Advanced Settings dialog. The dialog is accessed by clicking the Advanced button on the System - General page of the Preferences dialog.

Configuring the Color of Nets

Main article: Applying Color to the Nets

To help make the schematic more readable and make it easier to work with nets and routes in the PCB editor, color can be applied to schematic wiring, and the PCB nets and routes.

A highlight color can be applied to a net or a bus in the schematic editor using the commands in the View » Set Net Colors sub-menu, as shown in the image below. These colors can be transferred to the PCB editor at any time, via the Update PCB command.

In the PCB editor, the default color and visibility of the Connection Lines is configured in the System Colors section of the PCB View Configuration panel. Note that this default color is applied when the nets are created (during initial design transfer from schematic), the color of existing connection lines will not change if this option is changed.

In the PCB editor, the color applied to each net is displayed in the Nets mode of the PCB panel. Look for the color behind the checkbox next to the net name, as shown in the bottom right corner of the image below.

The color is always applied to the unrouted nets (connection lines). To display the color on the routed nets, enable the checkbox next to the net name in the PCB panel, and configure the display options in the Board Insight Color Overrides page of the Preferences dialog. In the image below, the override color Base Pattern is set to Solid, and the Zoom Out Behavior is set to Override Color Dominates.

Apply color to the nets in the schematic and PCB editors, to make it easier to examine the connectivity in each editorThe net colors applied in the schematic are transferred to the PCB by the Update PCB command. Configure the PCB Color Override features to control how they are displayed on the board.

Press F5 to toggle the Net Color Override feature on / off, in both the schematic and PCB editors. You may need to also perform a screen refresh (End).

Changing the Color of the PCB Nets

It is not always possible to apply color to the schematic wiring and transfer it to the PCB. In this situation, color can still be applied to connection lines and routing in the PCB editor. To change the color of a net after the design has been transferred, double click on the net name in the Nets mode of the PCB panel. The color of an individual net can be edited in the Edit Net dialog.

To change the color of multiple nets, use the Nets mode of the PCB panel:

  • Use standard Windows multi-select techniques (Shift+click or Ctrl+click) to select multiple net classes or multiple individual nets.
  • Right-click on a selected object and choose the Change Net Color command from the context menu, to assign a new color to the selected nets.
  • Right-click a second time and choose Display Override » Selected On, to enable the color override feature for the selected nets.

Net color can be applied directly in the PCB editor, when it is not possible to apply it in the schematic
Improve the visibility of nets by changing the color of their connection lines, and enabling the display override feature.

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