• The inputs (*IN) are open hi.
• The inputs are activated by pulling them to ground
• The inputs source 12mA when connected to ground
• A 2.2KOhm resistior pulls them well to ground.
• The output DOUT pulls to ground when signal is red
• YIN, RIN and DIN have effect immediately
• When DIN is set hi again the signal goes to green via yellow. The yellow period is influenced via a timer.

In the center there is a PIC that does the logic.

The signal is connected via RJ12 J3.

• The N scale signal has 3 aspects and needs thus 4 wires.
• Pin 1 and 6 of the RJ12 (R1 to AUX1 and R15 to PIC) are not connected to the signal
• The signal has common ground.
• The resistors R12,R13,R14 that are matched to the signals are on the signal control PCB, not part of the signal itself
• I did not check which color was which pin in J3.

Links:
Atlas PDF
The OEM provider for Atlas?