Erik:

The solution to your problem is to use an RJ31X type jack. This is an 8 wire type of modular jack that has shorting bars in it that permits the center two conductors to be shorted to the outer two connections when the plug is removed. These jacks are used primarly in the wiring of security panels into the office or home phone systems. It allows a phone line to pass through a jack when a security panel is unplugged from its jack.

Here is a schematic of the RJ31X type of jack.




Here is a link to a web page that describes the use of this type of jack when connecting up a security system.

<c>How Do I ... Wire an RJ31X Jack?</b.</c>

As you can see it is easy to use this type of jack to automatically disconnect the termination resistors in an RS-485 or an RS-422 network. With proper pinning selection you can support disconnecting 1 or 2 resistors for half duplex single pair setups or full duplex two pair setups.

You can look at DOLPHIN COMPONENTS CORPORATION as one possible source for these components.


Michael Karas