Telit FAQs, Part 17: Why does the STAT LED stay on during low power mode?

Question detail:

I am working on some firmware for putting the Telit CE-910 DUAL into low power mode.  The issue is we have an LED connected to GPIO_01 of the chip.  Normally, my FW sets this up to indicate network status.

I put the CE-910 into low power mode by doing the following:

Issuing AT+CFUN=5

Raising /DTR signal to a high voltage

The power level drops, as expected, and AT communication does not work when the chip is in this mode, as expected.  My issue is the GPIO_01 circuit turns the LED ON continuously.  I tried using the AT#GPIO=1,1,1 command, and this DOES turn the LED OFF when the modem is in normal mode (/DTR signal is low).  But as soon as I raise the /DTR signal the GPIO_01 driven LED goes on and stays on.

The LED is drawing about 30% of the system power consumption when the modem is in low power mode.  I would like to make it stay OFF in low power mode (or maybe just occasionally blink).

Answer:

The easiest way to avoid this issue is to set the GPIO to an input before you turn on power saving. For the xE910 modules, the STAT LED is located on GPIO 1, so we can set this to an input by issuing the command:

This command should be issued BEFORE putting the module into low power mode. After exiting low power mode, you can send the following command to reactivate the status LED: