Rainbow Electronics GM862-GPS - Manual (Page 54)

GM862-GPS Software User Guide
1vv0300729 Rev. 5 - 05/07/07
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3.4 GSM Power Saving function
The Telit GM862-GPS has a special function that reduces the power consumption during the idle time,
thus allowing a longer standby time with a given battery capacity.
This function monitors the DTR line indicating that the OEM application is ready to send commands,
when it goes high (3V on UART) then the OEM application is not going to send any commands and
the GM862-GPS module can save energy by shutting down its internal serial port.
When the OEM application becomes again ready, then the line DTR is tied low (0V on UART); the
GM862-GPS detects this condition and powers up the serial port.
If the power saving function is activated, then the serial port must support the DTR line since when this
line is high (Data Terminal is NOT ready) the device goes into a sleep condition and will not respond
to commands until the DTR is tied low (Data Terminal is ready).
NOTE: The power saving function does not affect the network behavior of the GM862-GPS,
even during the power save condition the module remains registered on the network and
reachable for incoming calls or SMS. If a call income during the power save, then the module
will wake up and proceed normally with the unsolicited incoming call code.
The DTR functionality is usable only when +CFUN=5 is selected.
TIP: When the GM862-GPS wakes up from the sleep mode, it takes a maximum of 150
milliseconds before it can exchange commands on the serial port. Hence place a delay of at
least 150 ms between the port opening (DTR lowering) and command sending.
According to the V24 standard, when the module is not ready to receive commands it will tie
up the CTS line, while it will pull it down when it's ready to receive commands; hence you can
monitor the CTS line to ensure the GM862-GPS is ready for commands.