Digi XBee 3 Cellular LTE-M, User Manual, Page: 143 / 331

Power saving features and design recommendations PSM behavior
Digi XBee® 3 Cellular LTE-M/NB-IoT Global Smart Modem User Guide 143
go into the PSM state on its own schedule. The XBee cannot and does not directly put the
cellular component into a PSM dormant state.
n
When waking from XBee sleep (such as Pin Sleep or Cyclic Sleep), if the cellular component is in
the PSM state (
AI = 0x2C), it remains in the PSM state until there is activity which triggers it to
wake up. In other words, XBee sleep is typically orthogonal to PSM.
Note In firmware versions ending in *16 and earlier, waking from XBee sleep would trigger the cellular
component to wake up. This was changed in firmware version *17 to ensure better power-saving
behavior.
PSM behavior
Commands exist to influence the PSM behavior when PSM is enabled ( DO bit 3 is set).
Note For NB-IoT, TCP and SMS support is dependent on the network. Contact your network provider
for details.
They are:
n
PA (Requested Active Timer)
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PU (Requested Tracking Area Update Timer)
PA and PU are the values the XBee Smart Modem requests from the network. The network is free to
assign values other than those which have been requested.
See the LTE-M Deployment Guide from GSMA for a description of what the PSM timers are and what
functions they perform on the network.
Low voltage shutdown
The XBee Smart Modem can monitor the XBee VCC line in order to detect a failing power supply.
Monitoring the VCC line can prevent possible memory corruption on both the cellular modem and the
file system due to insufficient power. This feature is recommended for users who run the XBee off of a
battery.
You must first enable this feature and then set a base threshold for the voltage on the XBee Vcc line.
When the voltage falls below the base threshold, the XBee goes into a shutdown state. When in a
shutdown state:
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The cellular modem will be shut down completely, halting any network activity.
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The file system will be shut down completely, disallowing any file system operations.
Once in this state, the XBee will resume normal functionality only after a reset. A reset is triggered if
the voltage rises above an upper threshold set by a combination of values.
Note The XBee VCC voltage gets read periodically, once every two minutes. Consequently, it may take
up to two minutes to change to or from a shutdown state.