Short Trace

The short-trace statement identifies two component pads that have a high affinity to one another. This most obvious example is bypass capacitors applied to supply pins.

This information is used in multiple places:

1. The placer uses this information to create an initial layout that places these pads close together.
2. The Board UI uses this information to make a unique rats nest representation.

This statement is only valid in the pcb-module context.

Signature

  short-trace(<REF-1>, <REF-2>)

• <REF-*> - The arguments to short-trace are expected to be refs to SinglePin ports of a component instance.
• Each port must be connected to the same net.
• Providing a ref to a pcb-module port will have no effect. The ref must be to a port on a component instance that maps to a physical pad of the component's land pattern.

Usage

The most common usage pattern for short-trace is for bypass capacitors.

pcb-module microcontroller:

  inst U1 : MCU

  inst C5 : ceramic-cap(0.1e-6) 

  net VDD (C5.p[1], U1.VDD)
  net GND (C5.p[2], U1.GND)

  short-trace(C5.p[1], U1.VDD)

If we examine what this looks like in the board view, we will see something like this:

Notice that the connection between C5 and the QFN package component, we see that the rat's nest has a blue hue to it. This is the signature for short-trace connections in the board view.

This is a very useful tool during layout for determining which bypass capacitors should be placed where. Instead of referring back to the schematic or the datasheet for a part, we can immediately know where a particular cap needs to go.