GE865 doesn’t respond to SABM(0) command

6 thoughts on “GE865 doesn’t respond to SABM(0) command

  1. I am working on a project, where I am using an XMEGA to control a Telit GE865-Quad module. I would like to establish CMUX communication protocol between the two, but am facing some difficulties with this. 


    In order to set the Telit module into CMUX mode I issue the following AT commands: 

    AT#SELINT = 2<CR>










    <CR><LF> OK<CR><LF> 

    After issuing these commands, I issue the SABM on channel 0 to which I don’t get any response from the modem. 

    To ensure that the SABM is being received by the modem, I enabled the command echo and then issued the SABM on channel 0. The hexadecimal log is as follows:

    F9 03 3F 01 1C F9  // SABM on DLCI = 0  issued

    F9 03 3F 01 1C F9  // Command echo


    I expect the modem to respond with either an UA or DM response ( I receive neither of these).

    If I do get a UA response, the SABM on channel 0 will be followed by a SABM on channel 1 and UIH MSC frame. 

    Am I missing something ? Why am I not getting a response to the SABM(0) ? any help with this would be much appreciated.

  2. I have just come to realize, from the most recent version of the CMUX user guide ( 1VV0300994 Rev. 2 – 2012-07-05 ), that the use of Hardware Flow control on the physical serial line that will support the Multiplexer Protocol is mandatory. I believe that this is the cause of the above problem. 

  3. Hi, you know I have the same problem, I’ve made active  Hardware Flow control but nothing.

    Also, I’ve read that:

     Note: after entering the Multiplexed Mode an inactive timer of five 

    seconds starts. If no CMUX control channel is established before this 

    inactivity timer expires the engine returns to AT Command Mode

     But I send  immediately.

  4. Hi Dmitriy,

    I worked with Steve on this problem. The problem is associated with the Modem’s mandatory requirement to have hardware flow control. Modem’s CTS and RTS has to be driven in order to get CMUX working.

    If you’ve got hardware flow control working, and are issuing the following SABM command on channel 0 within 5secs from issuing "AT+CMUX=0" :

    F9 03 3F 01 1C F9  // SABM on DLCI = 0  issued


    Then the modem should reply with:

    F9 03 73 01 07 F9


    At which point CMUX is established. If you fail to recieve this reponse, It may well be that there is an error in the At commands you issue leading upto CMUX intialising. 

    Following are the commands we issued: 

    >> ATE0&K3&D2&S0
    >> AT+IPR=9600
    >> AT#CMUXMODE=1

    >> AT+CMUX=0


    I hope this helps.  

  5. Thank you, all is ok! There are were another my  local problems, connected with wrong request. Your sugest has limited different  wrong ways and hase made me easier to find the problem.