E-Z Command Control Unit

[Signalman]

G'Day once again. Can anyone tell me what the I/O Port, "Cat 5" socket on this unit is used for, and how can it be used. Thanks in advance. Col.

[OldTimer]

If you look at the top of this page, you'll see four menus.  Click on "Parts and Service" and drill down into the EZ Command section.  You'll find a description of the I/O port and what it can be used for.
OldTimer

[ABC]

It is for the extra walk around companion(s), it will not work with anything else even though it may fit in the socket.