Installation guide

LMU Users Guide

V1.0.6 December 10 2009

- 96 - CalAmp Proprietary & Confidential

12.1.5.5 Checksum

Checksums are useful in detecting data transmission errors when the communication

channel is noisy. If provided, they are delimited from the rest of the sentence by a semicolon

and are always the last element of the sentence before the end delimiter.

;*AA<

The default mode of operation is to include checksums in sentences from the module. The

checksum itself is a two-byte ASCII representation of an eight-bit hexadecimal value. The

checksum is computed as the eXclusive Or (XOR) of all characters from the beginning of

the sentence (including the start delimiter) up to and including the asterisk (*) character in

the checksum protocol element. The LMU will accept all messages with a correct checksum

or with the checksum element omitted. Messages sent to the module with an incorrect

checksum will be disregarded.

The presence of the check sum is controlled by bit 0 of the TAIP Enables Parameter. To

include the checksum you would use:

AT$APP PARAM 2048,0,1,1

To omit the checksum, you would use:

AT$APP PARAM 2048,0,1,0

12.2

12.2.1 Enabling TAIP

TAIP Settings

The LMU-4100’s TAIP interface can be enabled and disabled, which differs from both the

LM Direct and SMS interfaces which are always on. In order for the LMU-4100 to create

and process TAIP messages, it must be enabled. This is done with bit 3 of the Service

Enables Parameter. To turn the TAIP interface on you would use:

AT$APP PARAM 1025,0,8,8

To disable the TAIP interface, the AT Command would be:

AT$APP PARAM 1025,0,8,0

If the TAIP interface is not enabled, the LMU-4100 will neither response nor react to any

incoming TAIP sentences, nor will it creates any sentences based on its reporting intervals.

12.2.2 Message Selection

As mentioned above, the LMU-4100 supports 3 TAIP sentences, LN, PV and IO. The lower

three bits of Parameter 2049 control which sentences will be created. If a bit is set, then the

associated sentence will be created as an automatic or PEG generated report. If the bit is

cleared, then the associated sentence will not be created. The bit mappings are as follows: