AT commands to connect T68i to a PSTN modem via CSD

Posted on 2004-11-16
Last Modified: 2013-12-09
I have Sony Ericsson T68i cell phone. I would like to use Sony Ericsson T68i (AT&T is the service provider) as GSM modem to connect to a PSTN modem. AT&T doesn’t support CSD. I guess I can use an ISP to establish a CSD connection with PSTN modem. Since ours is an embedded product with some real time operating system we will be using AT commands to connect the GSM modem to a PSTN modem. To test the concept I am using hyperterminal to communicate with T68i.
I know that I need to create a GSM data account on T68i. What is the AT commands sequence to establish a CSD connection with PSTN?
Thanks for your help.

Question by:narash
    LVL 3

    Expert Comment

    First check your modem to see if HSCSD is supported.


    You'll get back a series of numbers, e.g.
    +CHSD: 10,4,2,5,12
    That last # is important - it tells you the speed of the connection. "12" means supports either 9.6k or 14.4k.
    There are other things that you can configure - Reference GSM 07.07 section 6. Then it just behaves like any other dialup. Check your phone # from your ISP and you're ready.

    If your product is embedded then why not use an embedded modem?



    Author Comment

    Thank you for your response.
    I have read somewhere else also that refer section 6 for configuring GSM modem for CSD connection. Problem is we couldn’t find that manual. What is the manual name and where would we find it?
    When we gave AT+CHSD command it returned 2,2,1,3,12
    Do you have a sequence to configure the GSM modem (cell phone) to establish CSD connection?
    We are also looking for embedded modems.

    LVL 3

    Accepted Solution

    The GSM spec mentioned above can be found on the 3GPP web site:
    Download . It's an MS Word file.
    You can check the default config returned by +CHSD in the spec. If you need to change it for any reason the spec tells you several commands for doing that. After that nothing is needed other than just going off hook and ATDT like any other call. Check your ISP to see if they have special number for CSD users. There are plenty of application freeware/shareware already out there that writes to COMM port.

    Lastly you may wish to look into GPRS products, if you find the speed and bandwidth requirements are not met by CSD.  Some vendor links for embedded and m2m products are listed below.,1522,,00.html?orig=/m2m  have several products GPRS and CDMA, they're a smaller co. that you'll probably get much better support from. They'll even send you a free eval board.


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