Disabling Modem Tx and or Rx Using gpio4/at+cfun command

2 thoughts on “Disabling Modem Tx and or Rx Using gpio4/at+cfun command

    1. We need to temporaryly be able to disable Modem transmision when using another RF device on our platform. we using telit cmux driver and MS RIL / CellCore Radio stack.


      We decide to set GPIO4 as Modem RF Tx power control, so we can turn on/off as required. We dont want to disable modem by turning it off completly cause it will take longer to restart, and most importantly ril/cmux drivers loose sync with modem, so they LL have to be restarted too.

      1. Initialisation String


      "#GPIO=4,0,2;"

      Line above added to our modem init string to set gio4 as RF tx power control.

      2.

      We have added 47K pull up resistor to gpio4 for this as mentioned in ge865 data sheet, but is it also worth setting our gpio that drives gpio4 high in cmux driver before cmux driver starts modem intialisation

      we need to ensure modem RF tx is enabled intially after init string sent to modem

      when modem processes intialisation string and starts-up, we dont want modem starting up with RF tx disabled.

      3.

      Since we driving the gpio4 pin by software, might we be better off using CFUN=2 to control modem transmitter, if so can cfun=2 go into initialisation string, this not our preffered option though, only cause we got stuff in place for using gpi04, but any advice here is welcome.

      4.

      I assume we will loose GPRS network registration and attach when tx goes off using gpio4, but i hope it gets registered and attached automatically soon as we set gpio4 back high.

      Reading telit manual desciption of AT+CFUN =4 , seems to say modem remains registered and attached even in low power mode, does that mean modem still polling(using tx/rx) network in low power mode. I want to be able to totally disbale tx /rx without having to switch modem off, if possible.

      5.

      Also wondering what value we will get, if we request RSSI signal strength from modem while RF tx is off.

      Sorry for the essay, thanks for the reply in advance.