Purpose
This application note explains how to configure a Siretta modem to communicate with an analogue modem using a Circuit Switched Data (CSD) connection. Once configured, serial data can be transmitted between a remote system connected to the Siretta modem and another system connected through an analogue modem.
| Part Number | Description |
|---|---|
| ZETA-GEP-LTE4 (EU) | Low Power LTE Cat 4 European Modem with GPIO and GNSS |
| ZETA-G-GPRS | Entry Level GPRS Modem with GNSS (GL) |
| ZETA-N2-GPRS | Entry Level GPRS Modem (GL) |
| ZETA-NEP-LTE4 (EU) | Low Power LTE Cat 4 European Modem with GPIO |
| ZETA-NLP-LTE1 (EU) | Ultra Low Power European LTE Cat 1 Modem |
| ZETA-N-LTE (EU) | High Performance LTE Cat 4 Modem with GPIO |
| ZETA-NSP-LTE1 (EU) | Low Power European LTE Cat 1 Modem |
Circuit Switched Data is a dial-up style data connection used to transfer information between two systems. Instead of using packet-switched internet connectivity, the modem establishes a direct data call.
In this example, an analogue modem dials the CSD data number assigned to the SIM card fitted inside the Siretta modem. Once the call is answered, data entered at either terminal is passed to the other side.
Important Note
The SIM card must be provisioned for CSD by the network provider. A standard voice or packet-data SIM may not support this service unless CSD has specifically been enabled.
| Item | Description |
|---|---|
| CSD enabled SIM card | The SIM card must support Circuit Switched Data and must have a separate dialable data number. |
| Terminal emulator | Tera Term, HyperTerminal or PuTTY can be used to configure the modems using AT commands. |
| Siretta modem | The modem must support CSD operation. |
| Analogue modem | A standard analogue modem connected to a working telephone line. |
| RS232 cable | RS232 to USB or RS232 to RS232 cable, depending on the PC connection. |
| Two PCs | One PC connected to the Siretta modem and one PC connected to the analogue modem. |
| Working telephone line | Required for the analogue modem. |
| Siretta Modem Side | Connection | Analogue Modem Side |
|---|---|---|
| Siretta modem connected to PC or remote equipment using RS232. | CSD data call over the mobile network using the SIM data number. | Analogue modem connected to PC and working telephone line. |
Configure the COM port connected to the Siretta modem using the following settings.
| Setting | Value |
|---|---|
| Bits per second | 115200 |
| Data bits | 8 |
| Parity | None |
| Stop bits | 1 |
| Flow control | Hardware |
Note
These serial settings should also be used for the analogue modem terminal connection unless the analogue modem manufacturer specifies otherwise.
Enter the following AT commands into the terminal window connected to the Siretta modem.
| Command | Description |
|---|---|
AT#DIALMODE=2 |
Configures the modem for data dial mode. |
AT+FCLASS=0 |
Sets the modem to data mode. |
AT+CRC=1 |
Enables extended incoming call reporting. |
AT&K0 |
Configures flow control behaviour. |
ATS0=1 |
Sets the modem to answer automatically after one ring. |
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT#DIALMODE=2 |
Expected Result
The Siretta modem should return "OK" after each command. The modem is then configured to answer an incoming CSD data call.
| Setting | Value |
|---|---|
| Bits per second | 115200 |
| Data bits | 8 |
| Parity | None |
| Stop bits | 1 |
| Flow control | Hardware |
From the analogue modem terminal window, dial the CSD data number assigned to the SIM card inside the Siretta modem.
Command format: ATDxxxxxxxxxxx
Example: ATD07736393040
| Analogue Modem - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
ATD07736393040 |
Important Note
Replace "07736393040" with the actual CSD data number supplied by the network provider.
While the analogue modem is dialling, the terminal window connected to the Siretta modem should show an incoming data call indication.
| Siretta Modem - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
+CRING: REL ASYNC |
| Message | Meaning |
|---|---|
+CRING |
The modem has detected an incoming call. |
REL ASYNC |
The incoming call is an asynchronous data call. |
Expected Result
+CRING: REL ASYNCconfirms that the Siretta modem has detected an incoming asynchronous CSD data call.
After the configured number of rings, the Siretta modem answers the call automatically. Both terminal windows should show that a connection has been established.
| Analogue Modem - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
CONNECT 9600 |
| Siretta Modem - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
CONNECT |
Expected Result
Once both sides show "CONNECT" then the CSD call has been established and serial data can be exchanged.
The number of rings before the Siretta modem answers is controlled by the ATS0 command.
| Command | Result |
|---|---|
ATS0=0 |
Automatic answering disabled. |
ATS0=1 |
Answer after one ring. |
ATS0=2 |
Answer after two rings. |
ATS0=3 |
Answer after three rings. |
Example
If the modem should answer after two rings, useATS0=2.
Once the CSD connection is established, type text into either terminal window. The same text should appear in the opposite terminal window.
| Analogue Modem - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
Hello from analogue modem |
| Siretta Modem - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
Hello from analogue modem |
Expected Result
If the text entered into one terminal appears in the other terminal, the CSD data connection is working correctly.
After the CSD connection has been tested successfully, the PC connected to the Siretta modem can be replaced with the final remote system or equipment.
| During Testing | Final Installation |
|---|---|
| PC connected to the Siretta modem using a terminal emulator. | Remote equipment connected to the Siretta modem using RS232. |
| Manual test data entered through the terminal window. | Application data sent automatically by the connected equipment. |
| Analogue modem dials from a test PC. | Remote monitoring system dials the deployed Siretta modem. |
Deployment Note
Once deployed, the remote monitoring system can dial the Siretta modem using the CSD data number and communicate directly with the attached serial equipment.
| Problem | Possible Cause | Action |
|---|---|---|
| No response to AT commands | Incorrect COM port or serial cable issue. | Check the COM port number, cable connection and terminal emulator settings. |
| No incoming call shown | Incorrect number dialled or SIM not enabled for CSD. | Confirm the correct CSD data number with the network provider. |
| Call rings but does not answer | Automatic answering is not configured. | Use ATS0=1 or ATS0=2 on the Siretta modem. |
| Unreadable characters are displayed | Serial settings do not match. | Check baud rate, data bits, parity, stop bits and flow control on both sides. |
| No data is transferred | RS232 wiring or flow control issue. | Check TX, RX, GND and hardware flow control connections. |
| Connection drops unexpectedly | Poor signal or unsupported CSD service. | Check antenna connection, signal level and SIM provisioning. |
| Step | Action |
|---|---|
| 1 | Connect the Siretta modem to PC 1. |
| 2 | Connect the analogue modem to PC 2 and to a working telephone line. |
| 3 | Configure both terminal emulator COM ports. |
| 4 | Enter the Siretta modem AT command configuration. |
| 5 | Dial the Siretta modem CSD data number from the analogue modem. |
| 6 | Confirm +CRING: REL ASYNC appears on the Siretta modem terminal. |
| 7 | Confirm both modems show CONNECT. |
| 8 | Send test data in both directions. |
| 9 | Replace the test PC with the final remote equipment. |
Support
For further assistance, please contact the Siretta support team.