Boot-up sequence
The user application should ignore any characters received during startup until the following
NMEA sentence has been received:
$M138 BOOT,RUNNING*2a
The bootloader may output non-NMEA formatted messages during this time. These messages
include, but are not limited to: status messages, firmware update progress messages, and error
messages. These messages should be ignored and are for Swarm debugging purposes only.
GPS Date/Time Reference
The Modem will enter its GPS acquisition state once the boot-up sequence is complete. Please
refer to
Figure 11
for estimates of how long the Modem will take to acquire a valid date/time
reference. The user application should not send any transmit data ($TD) commands until the
following NMEA sentence has been received:
$M138 DATETIME*56
Figure 11
: Time Estimates for GPS Date/Time Reference Update
© 2022 SWARM TECHNOLOGIES
SWARM M138 MODEM PRODUCT MANUAL · REV 1.20 · FEBRUARY 2022
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