Bus

Parent page: Schematic Objects

A Bus is a polyline object that is used in conjunction with other objects to define the connection of multiple nets.

Summary

A bus is an electrical design primitive. It is a polyline object that represents a multi-wire connection.

Availability

Buses are available for placement in the Schematic Editor only by clicking Home | Circuit Elements | 

from the main menus.

Placement

After launching the command, the cursor will change to a cross-hair and you will enter bus placement mode. Placement is made by performing the following sequence of actions:

1. Click or press Enter to anchor the starting point for the bus.
2. Position the cursor and click or press Enter to anchor a series of vertex points that define the shape of the bus.
3. After placing the final vertex point, right-click or press Esc to complete placement of the bus.
4. Continue placing further bus objects, or right-click or press Esc to exit placement mode.
5. Use the Backspace or Delete keys to remove the last bus segment placed.

Placement Modes

When placing a bus there are three placement modes, two of which have Start and End sub-modes. The mode specifies how corners are created when placing buses and the angles at which buses can be placed. During placement:

• Press Shift+Spacebar to cycle through the 90 Degree, 45 Degree and Any Angle modes.
• While in the 90 Degree or 45 Degree mode (known as true orthogonal modes), press Spacebar to cycle between the Start and End sub-modes.
• During placement, the current placement mode is displayed in the Status bar. You can change modes at any time during bus placement.
• In modes other than Any Angle, the line segment attached to the cursor is a look ahead segment. The segment you are actually placing precedes this look ahead segment.

 45 degree mode

 90 degree mode

 Any angle mode

Press Shift+Spacebar to cycle through the different placement modes.

Guided wiring of a Bus

Schematics have a definable electrical grid that makes it easy to define electrical connections between objects. As you are placing a bus, when the bus falls within the electrical grid range of another electrical object, the cursor will snap to the fixed object and a Hot Spot (red cross) will appear.

Hot Spot (red cross)

The Hot Spot guides you to where a valid connection can be made and automatically snaps the cursor to electrical connection points.

The electrical grid can be defined on the Sheet Options tab of the Document Options dialog (Project | Content |

). It is recommended that you set the electrical grid to be slightly smaller than the current snap grid or it becomes difficult to position electrical objects one snap grid apart.

Graphical Editing

This method of editing allows you to select a placed bus object directly in the workspace and change its size and/or shape graphically.

When a bus object is selected, the following editing handles are available:

Selected Bus, ready for graphical editing.

• Click and drag A to reposition the end points of the bus.
• Click and drag B to move a bus vertex. The end points will remain anchored.
• Ctrl+click and drag on a bus segment to grab that segment and reposition it. The end points and other vertices will remain anchored.
• Right-click on a vertex point then choose the Edit Bus Vertex n command to access the Vertices tab of the Bus dialog, with the entry for the nth vertex selected ready for editing.
• Ctrl+click and hold on a bus segment, then press Insert on the keyboard to add a vertex at that point.
• Click and hold on a vertex, then press Delete on the keyboard to remove that vertex.

Non-Graphical Editing

The following methods of non-graphical editing are available:

Via an Associated Properties Dialog

Dialog page: Bus

This method of editing uses the Bus dialog to modify the properties of a Bus object.

Edit the properties of the Bus in the Bus dialog.

The dialog can be accessed during placement by pressing the Tab key.

After placement, the dialog can be accessed in one of the following ways:

• Double-click on the placed Bus object.
• Place the cursor over the Bus object, right-click then choose Properties from the context menu.

Via the SCH Inspector Panel

Panel page: SCH Inspector

The SCH Inspector panel enables you to interrogate and edit the properties of one or more design objects in the active document.

Understanding Bus Connectivity

A bus is used to bundle any number of nets. To do this, the following conditions must be met:

• Each individual net must be identified by a net label.
• The individual nets must be named using the standard naming pattern <Name><NumericalIdentifer1>, <Name><NumericalIdentifer2>, for example, Address0, Address1, ..., Address n.
• The bus that the individual nets join must be identified by a net label in the format <Name>[<StartingNumericalIdentifer>..<EndingNumericalIdentifier>], for example, Address[7..0], or LED[1..8].

Autojunctions

A T-junction in a bus is automatically connected by a junction.

Bus Entries

A bus entry is a short, diagonal section of wire. A bus entry has a single function to perform, that is to allow an individual net to be ripped out of a bus at the same location another individual net is also ripped out of the bus, as shown in the image below. If a bus entry was not used in this situation, the two individual nets would connect together, creating a short-circuit. If it is not necessary to rip two individual nets from the same location on a bus, they do not have to be used.

Use bus entries when the nets need to be ripped from both sides of the bus.