Logical connections are thin blue lines that specify which pads are to be electrically connected prior to creating traces that actually make the connections. For example, in the illustration below pins 2, 6, 7, 8 are one set of logical connections (one net), which means they are to be connected with traces. Pins 3 and 5 are another logical connection or net. Pins 1 and 4 are not logically connected to any other pins, so their net is Empty.
You can make a logical connection between any pads. For example you might want to make a logical connection between pin 12 of an IC and pin 1 of a resistor.
- Place footprints and/or pads.
- In the left toobar select the Logical Connection tool or press the N key.
- Click the first pad to be connected. As you move the mouse you will see a thin line.
- Click the second pad to be connected. A dialog appears.
- Click "Enter new name" and enter a name for the new net (e.g. "Ground", "+15V", "Sensor In", etc.).
- Click OK.
- If needed click additional pins belonging to the same net.
- When finished, right click.
- If desired, review the nets by choosing Nets | Edit Nets.
You can change which logical connection net a pin belongs to. For example you might decide that a certain pin of an IC should not be connected to a clock signal by removing the pin from a net named "Clock".
- Select the pad.
- On the Property bar select the desired net from the drop list.
- Or use Nets | Edit Nets.
To hide Logical Connection lines uncheck View | Layers | Net layer.
To leave a pin unconnected assign it to the Empty net.
To make sure you have added all needed traces watch for all Logical Connections lines to disappear.
To see which pads are unconnected to a specified pad move the Logical Connection tool over the specified pad and watch for highlighted pads.
If you try to connect pins that belong to different nets, a dialog will ask if you want to merge the nets or reassign connected pins.
When you connect two pins with the Logical Connections tool, the line you expect to see may be rerouted, but the electrical connection will be maintained. This occurs because pad2pad automatically minimizes the total length of the logical connection lines.
Double clicking a logical connection line causes the Edit net dialog to appear and show the net.