This application note details how to use an analogue circuit switched connection (CSD) between a Siretta Modem integrated to an existing system at a remote location and another modem at a different location for the purpose of data transmission or remote monitoring of the remote equipment.


  • CSD enabled sim card with separate data number
  • Terminal emulator such as Tera Term / Hyper Terminal or Putty for modem configurations using AT commands
  • Siretta Modem
  • Analog modem
  • RS232 to USB cable/ RS232 to RS232 cable
  • Working telephone line for analog modem

Device Setup

  1. Connect the Siretta Modem to the PC using the supplied RS232 to USB cable.
  2. Open Tera Term or terminal emulator of your choice
  3. Configure the COM port with the following settings for Siretta modems which support CSD which includes 2G / GSM and 3G / UMTS variants.
    • Bits per second: 115200
    • Data bits: 8
    • Parity: None
    • Stop bits: 1
    • Flow control: Hardware
  4. Open your terminal emulator on a PC that is attached to Siretta Modem and configure the Siretta modem using the following AT commands:
    • AT+FCLASS=0
    • AT+CRC=1
    • AT&K0
    • ATS0=1
  5. Open the terminal emulator on the PC that is attached to the Analog Modem and configure com port as step 4.
  6. Dial the Siretta modem using the ATD command followed by data number (ATDxxxxxxxxxx).
  7. While dialing is performed from the analogue mode you will see “+CRING: REL ASYNC” on the terminal window connected to the Siretta Modem indicating an incoming data call.
  8. After one ring a connection will be established between the analogue modem and the Siretta modem. You can set the number of rings to any value by altering value of ATS0=n, where n = 1,2,3,4 etc on the Siretta modem side.
  9. Both terminal windows will indicate that a CSD call has been established and data any sent from the analog modem will appear at the Siretta Modem and visa versa.

System Integration

Once you have tested the connection you can replace the terminal emulator attached to the Siretta Modem with your remote system and then use the same method on the analgue modem to obtain data from your equipment using CSD dialup data call.