Figure 4 1.  Example of a Dedicated CDU

include the selection of the lever arm source, flight instrument interface mode, and

aiding sensor control.

4.2.3.1.2  Multiple Dedicated CDU Operation

Control and display for a GPS receiver may involve more than one dedicated CDU. 

The design of a GPS receiver may incorporate two dedicated CDU interfaces and may

also provide a data link interface (e.g., MIL STD 1553) that can also be utilized for

control and display.  However, only one interface should be able to control and

manually initialize a GPS receiver at any given time.  A master CDU can be designated

by a software configuration connector strap as either a data bus or one of the dedicated

CDUs.  The master CDU is initially the "active" CDU when the receiver is powered up

and may always regain control from another CDU if it has relinquished control to that

unit.  A designator indicating the current active CDU should be stored in non volatile

memory so that it will not change as a result of a accidental power outage.  The active

CDU has the sole responsibility for control and manual initialization and thus has sole

responsibility for the following:

Receiver Mode Commands

Rendezvous Mode Selection

4 3