User's Guide

Teletrac, Inc. - Prism TM Information and Installation Guide
1622-0300 B1 3/18/04 55
few codes with similar function or features rather than being expected to
handle all codes with different with a variety of possible functions or features.
Code standardization should take into consideration both inbound and outbound message
usage. It should also consider the limitations within the System, the VLU, the MDT, and
the workstation software that force some messages to be reserved or identified for special
usage. For example, the MDT has built in limitations due to resource limitations and the
VLU has unchangeable firmware where codes force VLU behavior differences.
There are three forms of inbound messages: ACM which are also known as ECM or
canned inbound messages, RCM_A which are known as Form Fill message and LIM
which are variable length free form message, which can be either Form Fill or Free Text.
This paper focuses on only canned inbound messages. The Teletrac Air Interface
protocol restricts inbound canned messages to ACM 11-99 codes. There are other
message codes available for special services and emergency messages but have system
restrictions due to EMS (Episode Management System) services (i.e. ACM 235-Panic,
ACM 207-Stolen, ACM 167-Roadside Assistance, etc).
There are two types of outbound message that are called FCM and Long FCM. The FCM
codes are allocated by the Teletrac Air Interface Protocol and are not the subject of this
paper. However, this paper does address the usage of codes within the use of FCM 220,
221 and 222. To date all outbound canned messages sent to the MDT use the FCM 220
message and send one of 256 possible codes (0-255) within the message structure as a
canned message code.
Inbound Message Guidelines
As mentioned above the ACM 11-99 codes can be used for inbound canned messages.
From those available 89 message codes the following considerations must be made:
• The MDT supports 40 canned inbound messages.
• The MDT supports 10 emergency messages.
• The VLU has 4 inputs capable of 8 messages (each ON and OFF).
• The VLUplus & PRISM TM has zones requiring 2 messages each (zone entry
and exit).
• The VLUplus & PRISM TM will have common script functions like Power
Management and Tow-Away which require message codes.
• The VLUplus & PRISM TM uses code “0” for Store and Forwarded locations.
• The current system has allocated messages ACM 90-99 as alternate
notification messages.
• The RF VLU has special functionality for ACM 94, 97 and 99.
Although the system currently may not take advantage of these features or in the future
may change the definition, the standardization of codes should expect that the codes are
used as intended. The following table shows how the inbound message codes could be
allocated.