Modem Support Gets
The Data, Wherever It Is




Built-in Modem Support

The TOP Server supports the use of modems on all serial communications drivers.  Modem control is provided by a set of  modem tags.  Once modem operation is enabled for a project, a predefined set of modem tags becomes available to client applications.  The modem tags provide control of dialing, dial number, hang up and auto answer mode.  Additional modem tags provide the status of the modem connection.   Using these modem tags, client applications can be designed to control all aspects of a modem connection.  The TOP Server’s modem support allows you to extend your system management and data gathering needs beyond the control room. 

Application Note: Using TOP Server with Standard Modems

System Tags for Modems - See here for more on how System Tags work

Syntax Example: <Channel Name>.<Device Name>._Modem._Dial

Tag Name



Writing any value to this tag initiates dialing of the current PhoneNumber. The Write is ignored unless the current Status is 3 (Idle). An error is reported if the current phone number has not been initialized. Attempting to issue a dial command while the Mode tag is set to 2 (incoming call only) will generate an error.


The DialNumber tag shows the phone number that is actually dialed, after any dialing preference translations have been applied (such as the addition of an area code). This tag is intended for debugging purposes. It can provide useful feedback to an operator if phone numbers are entered manually.


Writing any value to this tag hangs up the current connection. The "Hangup" tag will also hang-up the current connection when an external device has called the server. Writes to the "Hangup" tag will be ignored if the Status <= 3 (Idle) meaning that there is no currently open connection.


Whenever the Status changes, the reason for the change is set in this tag as a number. See TOP Server help file for details.


This allows for configuring the line for calling only, answering only or both.

Writing a 1 to the Mode tag sets the line for outgoing calls only, no incoming calls will be answered when in this mode. Writing a 2 to the Mode tag sets the line for incoming calls only, requests to dial out (Writes to the Dial tag) are ignored. The default setting is 0, which allows for both outgoing and incoming calls.

This value can only be changed when the Status is <= 3 (Idle).


This is the current phone number that will be dialed. Users can Write to this value at any time, but the change is only effective if Status is <= 3 (Idle). If users Write to the phone number while the status is greater than 3, the number will be queued. As soon as the status drops to 3 or less, the new number will be transferred to the tag. The queue is of size 1, so only the last phone number written will be remembered.

The phone number must be in canonical format in order to apply the dialing preferences. If the canonical format is used, the resulting number that will be dialed (after dialing preferences have been applied) can be displayed as the DialNumber.

Canonical format is the following:
+<country code>[space](<area code>)[space]<phone number>

example: +1 (207) 846-5881

Note: The country code for the U.S. is 1.

If the number is not in canonical form, dialing preferences will not be applied. The number will be dialed exactly as it is entered. Users can also enter a Phonebook tag name instead of a phone number. In this case, the current value of the phonebook tag will be used.


This is the current status of the modem assigned to a channel.


This contains a textual representation of the LastEvent tag value.


This contains a textual representation of the Status tag value.



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