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4 OPERATIONAL BASICS
4.1
Operational principles
TMT250 module is designed to acquire records and send them to the server. Records
contain GNSS data and I/O information. Module uses GNSS receiver to acquire GNSS data and is
run in three (time-based, distance-based and angle-based) acquisition modes. Please note that if
TMT250 loses connection to GNSS satellites it continues to make records, however coordinate in
these records remains the same (last known coordinate). All data is stored into flash memory and
later can be transmitted via GPRS.
GPRS and SMS settings are described in following sections. TMT250 communicates with
server using a special data protocol. TMT250 can be managed by SMS commands, which are
described in SMS command section.
4.2
Sleep modes
There are four sleep modes: GPS sleep, Deep sleep, Online Deep sleep and Ultra Deep
sleep mode.
4.2.1 GPS Sleep mode
TMT250 is able to go into GPS sleep mode if such mode is enabled.
Sleep mode timeout starts counting when device is in STOP mode. After timeout is reached
and all conditions for GPS sleep mode are met, the device goes into sleep mode. When in GPS
sleep mode, TMT250 turns GPS module off and continues making new periodic records. As a
result power usage decreases, in turn saving vehicle battery.
TMT250 will enter GPS sleep mode if ALL of these conditions are met:
▪ TMT250 is configured to work in GPS Sleep mode and sleep timeout is reached;
▪ Device time is synchronized with GNSS satellites and GPS fix is obtained;
▪ Movement is not detected by the accelerometer;
▪ Forced wakeup is not set;
▪ There are no SMS messages being received.
TMT250 exits GPS sleep mode if following condition is true:
▪ Movement by accelerometer is detected.
4.2.2 Deep Sleep mode
When in deep sleep mode, TMT250 sets the GNSS receiver to sleep mode and turns off
GSM/GPRS module (hence it is not possible to wake up device via SMS). Despite records with last
known coordinate being saved and sent to AVL server (GSM/GPRS module is turned on to send
data and then it is turned off), power usage is decreased to save vehicle's battery. Please note
that power saving depends on two configurable parameters: Send Period and Minimum Record
Saving Period in "X on Stop Mode". When records are sent successfully in deep sleep mode, open
link timeout counter will be skipped and TMT250 will enter deep sleep mode immediately.
Because a lot of functions are disabled in deep sleep mode following I/O elements are
disabled from records that are generated in this mode: GSM Signal, GNSS Status, GNSS PDOP,
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