Entry type: FAQ, Entry ID: 29975541, Entry date: 07/24/2008

How should you parameterize a GSM modem to set up a connection from an analog modem for teleservicing an S7-200?

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GSM (Global System for Mobile Communications) modems need a data type identification for connection set up for CSD (Circuit Switched Data) communication. This data type ID is provided in a connection setup with a GSM or ISDN modem, but not in attempts to set up a connection from an analog landline network. For this, you need either a SIM card enabled for GSM data communication (you must request a separate data number from the provider) or your GSM modem must have a setting to enable it to interpret all incoming calls as data communication.

For example, the SIPLUS GSM modem MC45T and the SIPLUS GSM modem TC65T have this setting option.

Proceed as follows to check the type of incoming call and set your GSM modem to be able to interpret all incoming analog calls as data communication.

No. Remarks
1 Set up connection from "HyperTerminal" to the modem
Connect the GSM modem via a modem cable to the serial port of your computer. Start the Windows "HyperTerminal" component via "Start > All Programs > Accessories > Communications".
2 Specify a name of your choice for "Connection Description" and acknowledge with "OK".
For "Connect using" you select the COM port that you have used to connect the modem.
For "Bits per second:" you select the connection speed currently set on your modem and then click "OK".

Fig. 01

3 "HyperTerminal" is no connected with the modem (provided that the settings are correct). However, to view the characters entered also in "HyperTerminal", you must activate the command output via "File" -> "Properties" -> "Settings" -> "ASCII Setup...", make the setting "Echo typed characters locally" and acknowledge with "OK".

Fig. 02

4 You can check the correct setting for the baud rate with the "AT" command. If successful, the modem responds with "OK".

If this is not the case, clear down the connection via the "Disconnect" button, change the baud rate via "File" -> "Properties" -> "Connect To" -> "Configure...", acknowledge twice with "OK" and set up the connection again via the "Call" button. Use the "AT" command to keep on checking until the modem responds with "OK".

If the typed characters are displayed double in "HyperTerminal", then the echo is also activated in the modem (command "ATE1"). In this case, disable the additional echo in the modem with the command "ATE0".

Fig. 03

5 Transfer PIN
To make the modem accessible you must log it into the mobile network with PIN transfer.
Use the command "AT+CPIN?" to query the network login status. If the modem responds with "+CPIN: SIM PIN", the modem is not yet logged into the network. Transfer the PIN for the SIM card inserted using the command "AT+CPIN=1234" (where "1234" stands for your PIN). Repeat your login status query and the modem now responds with "+CPIN: READY" (provided you enter the correct PIN). The GSM modem is now accessible.

Fig. 04

6 Display type ID of incoming call
Display of the type ID of the incoming call is disabled by default ex factory. You can check this using the command "AT+CRC?". The modem responds with "+CRC: 0" for disabled display or "+CRC: 1" for enabled display of call type ID. If the display is disabled, "HyperTerminal" outputs just the text "RING" for an incoming call signal. Use the command "AT+CRC=1" to enable display of the call type ID. Now, with an incoming call signal the text "+CRING: VOICE" is displayed for an ISDN or GSM voice call.

Fig. 05

7 Set data type interpretation of all analog calls
Use the command "AT+CSNS=?" to see whether your modem supports type interpretation of all calls without transferred type ID. If it supports this function, the modem responds with "OK". (0,2,4)". The digits in brackets indicate the possible settings: "0" for voice, "2" for fax and "4" for data call interpretation. Use the command "AT+CSNS?" to determine the current presetting. By default, most modems are set to voice call identification for calls without type ID transfer ("+CSNS: 0"). Set the type ID interpretation of all calls without type ID transfer to data call identification ("AT+CSNS=4"). Now, all calls that do not already have a type ID from the provider are interpreted as data calls ("+CRING: REL ASYNC").

Fig. 06

8 Terminate the "HyperTerminal" connection via the "Disconnect" button.
Now connect your GSM modem again via PPI multi-master cable to the S7-200 CPU to be teleserviced.
When the teleservice communication is set up in STEP 7 Micro/WIN via an analog modem, the GSM modem now interprets the call as data type and the connection is set up successfully (provided no type ID is supplied by the provider).
Table 01

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