6
M2303-00-P00-805
March 2003
2
Operation
Features
The A76 modem in the T201X radio performs the following AVL functions:
•
AVL data collection from the GPS receiver
•
simple AVL polling by the despatcher radio
•
group AVL polling by the despatcher radio
•
emergency unsolicited AVL reports to the despatcher radio
•
PTT generated AVL reports
•
AVL data transfer to another radio using the CCDI over-air protocol
•
A76 configuration database modifications using Tait proprietary NMEA style messages
•
auxiliary output control using RS232 CTS line
•
FFSK tone blanking when data received
•
reads the version of A76 firmware over-air
•
programs the Group Delay Time over-air so that group polling can be configured
•
reads the programmed Group Delay Time setting over-air
•
over-air reset of the remote radio with or without initiating database
AVL Data Collection
The A76 modem collects and stores NMEA RMC data at intervals set by the GPS receiver. When a AVL poll is
sent from the AVL application to the remote AVL radio or an emergency activation occurs, an AVL report with
the stored data is immediately sent to the despatcher radio and saved by the AVL application. Refer to the
section
, NMEA-0183 RMC Sentence Format,
for a description of the NMEA RCM format. All RMC fields are
initialised with ‘0’.
Radio Signalling
The signalling between the despatcher radio and the remote AVL radio uses the Tait CCDI V2.0 terminal and
over-air protocol. CCDI Short Data Messages (SDMs) are used to send commands to the remote AVL radio and
to pass information back to the central control computer.
Auxiliary Output
The auxiliary output from the A76 uses the RS232 CTS line on the serial port to switch external devices on or
off. It can be remotely controlled by the despatcher radio by sending a AUX ON or AUX OFF message. Refer to
the
Auxiliary Output Control
section. This feature can be enabled or disabled by the A76 configuration.
Emergency Mode
Emergency mode is activated by the RTS input on the A76 serial port. If asserted, the A76 enters Emergency
mode and sends unsolicited reports at preset intervals. Refer to the
Emergency Mode Activation
section.
The Emergency mode feature can be enabled or disabled by the A76 configuration.
