Basic AT modem characteristics

Modems may have a lot of different characteristics: design, supported data transfer protocols, error correction protocols, voice and fax communication.

TAPI – General information

TAPI stands for Telephony Application Programming Interface. TAPI comprises a lot of functions allowing devices transferring data over telephone lines to be programmed in a way independent of a specific device allowing users to communicate by phone. TAPI supports voice and data transfer and provides for a lot of connection types and call management. TAPI allows applications to use the functions of a phone, for example, support conferences and transfer voice mail. Applications rely on existing telephony service providers that provide TSPI (Telephony Service Provider Interface). The user can install any number of telephony service providers if only they do not access the same device at the same time. The user associates a device with a service provider during installation.

Some providers can access several devices. Sometimes the user may need to install the driver of a device together with the provider.

How the program works

After the program is loaded, it analyzes the task list. If the task list has at least one active task in it and it is due, it starts performing it. Exception: a task of the "On start" type is activated right after the program is loaded. After the program establishes a connection, it receives/sends data using the established connection. If there is no data and the timeout specified in the "Break the connection" task with the "The module didn't send/receive the data" condition expires, the connection is broken. A connection can also be broken in case the interval specified in the "Break the connection" task with the "After the connection was established" condition expires. Note that the "Break the connection" task with the "The module didn't send/receive the data" condition resets the timeout each time the program receives or sends data. In other cases, a connection is established and broken according to the specified task parameters.

Data exchange is carried out according to a task schedule (see "Schedule management"). If there is no TAPI driver for your modem, you can use the AT mode. It is recommended to use the TAPI mode in other cases.

AT modem settings

Select the "Modem settings" tab in the Settings dialog box and select the "AT-modem" device type in the drop-down list on this tab. As a result, you will see AT modem settings. Use the AT settings drop-down list to select one of the following settings:

AT modem general settings:

Fig. 1. AT modem general settings

Modem initialization lines – the list contains the modem initialize lines (a string of not more than 255 characters). The list allows you to add, remove, edit and move modem AT commands. These AT commands are used to initialize the modem before dialing a number. The following buttons for managing the lines are located to the right from the list:

- add a new initialization line to the list. After you click this button, the dialog box where you should enter the initialization line and click the <OK> button appears. If you enter an empty string or the initialization line is already in the list, the corresponding message will appear on the screen.

- remove the initialization line selected in the list. After you click this button, the confirmation dialog box appears. You should click the <Yes> button in this dialog box to remove the line or the <No> button to cancel the operation. If there are no initialization lines, this operation is unavailable.

- edit the initialization line selected in the list. After you click this button, the dialog box where you should edit the initialization line and click the <OK> button appears. If you enter an empty string or the initialization line is already in the list, the corresponding message will appear on the screen. If there are no initialization lines, this operation is unavailable.

- move the selected initialization line one position up. If there are no initialization lines, or if there is only one initialization line, or if the initialization line is the first one in the list, this operation is unavailable.

- move the selected initialization line one position down. If there are no initialization lines, or if there is only one initialization line, or if the initialization line is the last one in the list, this operation is unavailable.

Tone dialing – the checkbox enables/disables tone dialing. It is disabled by default.

Mute modem speaker – the checkbox enables/disables the internal modem speaker. It is disabled by default.

AT modem port settings:

Fig. 2. AT modem port settings

Name – the list allows you to select the com port the modem uses to connect to the remote terminal. All ports available in the system are displayed in the drop-down list. If there are no ports in the system, the list will be empty. If the port currently selected in the program is removed from the system and the program is started again, the removed port will be highlighted in red. The default is the first port in the list.

Baud rate – the list allows you to select one of the standard data transfer baud rates via the RS232 interface. The default is 9600 baud/sec.

Data bits – the list allows you to select the number of bits in a byte used to receive/send data. Do not use the following combinations: data bits  5 – stop bits - 2; data bits 6, 7, 8 – stop bits 1.5. 8 is selected by default.

Stop bits – the list allows you to select the number of stop bits for one character. Do not use the following combinations: data bits  5 – stop bits - 2; data bits 6, 7, 8 – stop bits 1.5. 1 is selected by default.

Parity – the list allows you to select the parity check. There is no check by default.

DTR – the checkbox enables/disables the DTR signal. It is disabled by default.

RTS – the checkbox enables/disables the RTS signal. It is disabled by default.

DSR sensitivity – if the checkbox is selected, the program ignores all data received from the modem as long as the DSR signal is set. It is disabled by default.

 
X continue OnXOff – the checkbox enables/disables transferring data when the buffer is full and the driver has sent the XOffChar character. If the checkbox is selected, the transfer will continue when the number of data bytes in the incoming data buffer will be less than XOffLim and the driver sends the XOffChar character. If the checkbox is not selected, transferring data to the program will not be continued till the number of data bytes in the incoming data buffer is greater than or equal to XOffLim and the driver sends the XOnChar character for resuming the data transfer. It is disabled by default.

 
Handshake – the list allows you to select the flow control type that can be software (XON/XOFF) or hardware (RTS/CTS or DTR/DSR). There is no flow control by default.

 
XOff char – this field allows you to enter the hexadecimal code of the XOff character (the character of disabling the data transfer) for receiving and sending data. The character code is specified in the #КС format, where # is the code sign, КС is the character code. It is #19 by default.

 
XOff char – this field allows you to enter the hexadecimal code of the XOff character (the character of enabling the data transfer) for receiving and sending data. The character code is specified in the #КС format, where # is the code sign, КС is the character code. It is #17 by default.

TAPI device settings

Select the "Modem settings" tab in the Settings dialog box and select the "TAPI-device" device type in the drop-down list on this tab. As a result, you will see TAPI settings. Use the TAPI settings drop-down list to select one of the following settings:

TAPI device general settings:

Fig. 3. TAPI device general settings

Device – the list allows you to select the TAPI device that is used to call the remote terminal. The list shows only devices supporting data transfer. The list may be empty if there are no such devices in the system. If the device currently selected in the program is removed from the system and the program is started again, the removed device will be highlighted in red. The default is the first device in the list.

TAPI device options:

Fig. 4. TAPI device options

Auto free idle calls – the input field allows you to close connections that have no actions for them (data transfer, etc.) for the specified interval. It is set to -1 by default.

Auto drop disc calls – the input field enables/disables automatically closing a connection upon disconnection. When the connection is switched to the "Disconnected" status, it will be automatically closed after the specified timeout expires (in milliseconds). If the parameter is set to -1, this feature will not be used.

Reply timeout – since some TAPI functions (calling, dialing, etc.) may take quite a while, the program calls these functions in the asynchronous mode (i.e. it does not wait till these functions finish their work, but continues its work). However, the program uses this timeout to control the work of the called operations. If the requested operation (calling, dialing, etc.) is not finished within the specified timeout, it will be canceled and the program will display the corresponding error message.

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