Sierra Wireless EV-DO - Manual (Page 60)

PinPoint-E EV-DO
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Wiring the PinPoint-E for DTR Event
Trigger
Following the directions in for wiring a switch to the serial
port to the DTR pin of the serial port, commonly a contact or
voltage controlled by the key switch, you can configure the
PinPoint‐E to change the power mode in response to the
ignition or any other specific event.
Caution: If either DTR or RTS have been configured to be used as
digital inputs, then low power mode cannot be configured to respond
to DTR.
Power Effect on Modem State
Once the transition from powered on to standby, low‐power
mode starts, the modem will change state to AT mode. This
results in the current mode being gracefully terminated. For
the brief period when the modem is preparing for low‐power
mode, the modem will remain in AT mode. At that time, it
wonʹt auto‐answer, ATD will fail, etc. Once low‐power mode is
entered, the modem will then discard any data received on the
host port.
When the modem is woken from low‐power mode, the same
behavior occurs as upon power on. The modem starts in AT
mode, and then after 5 seconds will enter the default start‐up
mode as it is configured for the modem.