I have three fastrack command controlled 072 switches on my layout that I operate with the iPad LCS app. They work great together with one exception. The app does not know if the switch is in the through or out position after it is triggered by the anti-derail function or even upon start up of the layout. I guess there is no feedback from the command controlled switch to the LCS system to indicate switch position. This will cause some issues for using this app as your only control panel. You will need to have some kind of indicator light or your switch controllers mounted to make sure you know how they are thrown if you do not have a good view of the lanterns. It seems to me that Lionel would need to add some type of feedback from the command switches or the ASC2 for none command switches.
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Here is a response from our customer service center – I hope this helps:
It is the data and com line, similar to the command base cable used to drive devices such as ASC/AMC/ARC, etc. The Data terminal is essentially a +5VDC communication line used to drive the old IC Controls line of devices, so a cable does not need to be run from the command base. If a command switch is in a close proximity to these devices you can use DAT and common to drive those devices.