Another means of precise time transfer from the GPS receiver is to use the 1 pulse per

second output in conjunction with the PTTI output message available on the MIL STD 

1553 multiplex bus.

4.4  ROLL/PITCH/HEADING/WATER SPEED ANALOG INPUT INTERFACE

A shipborne receiver should be able to accept analog inputs of the ship s attitude and

water speed in coarse and fine synchro for mat.  The heading input signal can be used

by the receiver to assist in satellite acquisition and tracking, and for relative course

calculations.  The roll/pitch input signal can be used by the receiver to compensate for

antenna motion.  The water speed input signal can be used by the receiver to aid in

satellite acquisition and tracking, and for relative speed calcu lations.

4.5  INSTRUMENTATION PORT INTERFACE

GPS receivers typically have an interface for testing during development and

manufacturing. If the configuration of this interface is documented and controlled, it

may be useful for integration purposes.  Several U.S. DoD GPS receivers have an

instrumentation port interface.   This interface can be used for some HV integration

applications and for connection  of test equipment used by maintenance and test

activities.  The interface is a full duplex RS 422 serial interface that can be con  

nected to a Smart Buffer Box for test instrumentation purposes, or to an

Intermediate Level Test Set for maintenance purposes.

4.6  RS 232 INTERFACE

RS 232 is a common interface typically used to interface between computer equipment.

 The PLGR includes a RS 232 2 way serial port.  This port provides the  capability to

control the PLGR remotely, and to transfer data between PLGRs or between  a PLGR

and a computer.  This interface can also be used for reprogramming PLGR  operational

software.

4.7  BAROMETRIC ALTIMETER INTERFACE

A variety of barometric altimeter devices output digitally encoded pressure altitude,

referenced to the geoid or Mean Sea Level (MSL), with a pressure reference of 1013.2

hectoPascals (formerly millibars).  This is the same encoded altitude as is used in

Mode C altitude reporting via an air traffic control radar beacon (IFF transponder). 

Some U.S. DoD GPS receivers have a compatible baro altimeter input.  It is a parallel

interface which consists of ten signal leads and one signal return.  The seven most

significant bits are a Gray Code representation of the barometric alti tude in feet, to the

nearest 500 feet.  The three least signifi cant bits are a binary code which indicates the

100 foot increment within the 500 foot interval.

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