Installation guide

LMU Users Guide

V1.0.6 December 10 2009

- 60 - CalAmp Proprietary & Confidential

Obviously one of the most important pieces of the LMU is the GPS Receiver. This section

describes the supporting features that exist outside of PEG which can affect the behavior of

the GPS Receiver.

Working with GPS

9.1

One of the more common uses of a GPS Receiver is to feed NMEA data into a real-time

mapping application that is running on a laptop or PDA. The LMU’s support of this feature

is described in the Working with Serial Devices section.

NMEA Messaging

9.2

The LMU has 3 timers which affect the behavior and status of the GPS Receiver.

GPS Timeouts

9.2.1 Last Known Timeout

This timer affects the contents of the Fix Status byte of an LM Direct message. The Fix

Status is meant to describe the GPS data being reported in the LM Direct message. This

specific timer controls how long the LMU will wait before setting the Last Known bit of the

Fix Status byte after losing GPS lock. When the LMU regains lock, the Fix Status byte is

immediately cleared.

The purpose of the delay is to handle cases of temporary outages, such as the LMU

travelling under a bridge or through a short tunnel.

The Last Know Timeout is controlled by Parameter 1028 and is defaulted to 60s. The value

of this Parameter is in seconds. For example, to set it to 45s you would use:

AT$APP PARAM 1028,0,45

9.2.2 GPS Lost

This timer effect when the GPS Lost PEG Trigger is fired. Like the Last Known Timer, it

starts when the LMU loses GPS lock. When the Timer expires, the GPS Lost PEG Trigger

is fired. If the LMU regains GPS while the Timer is active, the Timer is immediately stopped

and reset to its starting value.

This feature is to prevent excessive GPS triggers during temporary GPS outages (e.g. driving

under a bridge or through a short tunnel).

This Timer is controlled by Parameter 1027 and is defaulted to 60s. The value of this

Parameter is stored in seconds. For example to set the timer to 90s you would use:

AT$APP PARAM 1027,0,90