CHAPTER 4:  GPS RECEIVER INTERFACES

 AND ANCILLARY EQUIPMENT

4.1  INTRODUCTION

GPS receivers often require electrical interfaces with other components of the GPS

receiver system or with other systems in a host vehicle (HV).  Virtually all vehicle

integrations will require interfaces with HV power and an external antenna.  Many

will require a crypto key interface and control and display interfaces between an

equipment compartment and a crew compartment.  Some will require interfaces

between a data loader and the GPS receiver. Others may require interfaces

between the GPS receiver and other navigation systems in order to develop an

integrated position solution.  In order to accommodate the varied requirements of

different installations, a GPS receiver may be built with a variety of interfaces to aid

integration.  This chapter presents some thoughts on the ways of integrating GPS

with other systems using the interfaces specified for many of the U.S. DoD

receivers. These interfaces are also used by other NATO Nations and are provided

by other manufacturers, and therefore give an indication of what type of interfaces

could be available in a military GPS receiver.  Examples of U.S. DoD ancillary

equipment are also provided to clarify interface uses.

4.2 GENERAL PURPOSE INTERFACES

Two of the most used interfaces in a vehicle integration are the MIL STD 1553

multiplex data bus and the ARINC 429 digital information transfer system.  Both

interfaces can be used to interconnect a GPS receiver with a wide variety of other

equipment, for example, a control and display unit (CDU), data loader, flight

instrument interface unit, or other navigation system such as an INS.

4.2.1  MIL STD 1553 Multiplex Data Bus

Some GPS receivers are designed to communicate with other equipment via a MIL 

STD 1553 interface.  The MIL STD 1553 data bus is commonly used aboard

military aircraft and can also be found aboard military ground vehicles, ships, and

missiles.  It is seldom used for civilian applications.  The MIL STD 1553 bus

operates with one of the interconnected equipment units assigned as a bus

controller.  The bus controller controls the data flow on the bus in an asynchronous

command/response mode, and also transmits and receives information.  The other

units are connected to the bus function as "slaved" remote terminals that receive

and transmit information, but may also function as back up bus controllers.  The

bus controller software program is specifically designed for each unique

installation.

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