A Signal Control System specifically the Atlas USCB is the brains of the Atlas Signal System. Let's take a look at the System.
Careful review of this board reveals four “jumpers” labeled JP1 through JP4. Jumpers are small removable black plastic pieces with metal inside them which cover pins that controls the signal wired to the board.
In general, a jumper makes the board compatible to the signal and enables the operation of the desired option. The new Atlas USCBs, item# 70 000 046, are default set from the factory to provide appropriate stand-alone operation for most cases.
The only exception is JP2 which controls the two ways model railroad signals are usually wired, either common anode or common cathode.
The Atlas USCB allows either anode or cathode to be used by setting the JP2 jumper. Signal manufacturers typically provide this information on their packaging. The chart on page 15 lists the settings you should use for all current Atlas signals. If you are using earlier
Atlas signals, those were common cathode. Original BLMA signals were common anode.
If cathode, pins 2 and 3 will be covered by the jumper, if anode pins 1 and 2 should be cov- ered by the jumper. See Figure 2, page 6