Each frame contains zero or more values, each of which is called a signal. For example, the first two bytes of a frame payload may represent a temperature, and the third payload byte may represent a pressure. Within the database, each signal specifies its name, position, and length of the raw bits in the frame, and a scaling formula to convert raw bits to/from a physical unit. The physical unit uses a LabVIEW double-precision floating-point numeric type. The signal is the highest level of abstraction for embedded networks. When you use an XNET Session to read/write signal values as physical units, your application does not need to be concerned with protocol (CAN/FlexRay/LIN) details and frame encoding.

Use the XNET Signal I/O name to select a signal, access properties, and invoke methods. For general information about I/O names, such as when to use them, refer to NI-XNET I/O Names.

User Interface

Before using the signal I/O name, you must use Select Database to select a cluster within a known database. Because the NI-XNET hardware interface physically connects to a single cluster in your embedded system, it makes sense to limit the list to signals contained in a single cluster.

When you select the drop-down arrow on the right side of the I/O name, you see a list of all signals within the selected cluster, followed by a separator (line), then a list of menu items.

Each signal in the drop-down list uses the syntax specified in String Use.

You can select a signal from the drop-down list or by typing the name. As you type a name, LabVIEW selects the closest match from the list.

Right-clicking the I/O name displays a menu of LabVIEW items and items specific to NI-XNET.

The XNET Signal I/O name provides the following menu items in right-click and drop-down menus:

  • Select Database: In the drop-down list, this menu item opens a dialog to select a cluster. In the right-click menu, this item provides a pull-right menu to select the cluster. You must select a cluster to specify the signal selection scope. The list of clusters uses the same list as the XNET Cluster I/O name. Each cluster name typically is just the database <alias> only, but when a FIBEX file is used, each <alias>.<cluster> name is listed.
  • Browse For Database File: If you have an existing CANdb (.dbc), FIBEX (.xml), AUTOSAR ( .arxml), LIN Description File (.ldf), or NI-CAN ( .ncd ) database file, select this item to add an alias to NI-XNET. Use the file dialog to browse to the database file on your system. When you select OK, NI-XNET adds an alias to the file. The alias uses the filename, such as MyDatabase for a file path of C:\Embedded\Vehicle5\MyDatabase.dbc. If the alias is not unique, NI-XNET appends a number per LabVIEW conventions (for example, MyDatabase 2 ). After adding the alias, you can select the objects in that database from any NI-XNET I/O name.After adding the alias, it appears in the Select Database list, and the first cluster in the database is selected automatically.
  • New XNET Database: If you do not have an existing database file, select this item to launch the NI-XNET Database Editor. You can use the NI-XNET Database Editor to create objects for the database and then save to a file. When you save the file, the NI-XNET Database Editor also adds an alias. Therefore, after you save from the editor, the clusters in the database become available in the Select Database list. You must select the desired cluster when you finish using the NI-XNET Database Editor.
  • Edit XNET Database : If you have selected a cluster using Select Database, select this item to launch the NI-XNET Database Editor with that cluster's database file. You can use the editor to make changes to the database file, including the signals.
  • Manage Database Aliases: Select this menu item to open a dialog to manage aliases. You can review your list of aliases and associated file paths, remove an alias (without deleting the file), and add new aliases.If you are using LabVIEW Real-Time (RT), you can right-click the RT target within a LabVIEW Project and select the Connect menu item. This connects to the RT target over TCP/IP, which in turn enables the user interface of NI-XNET I/O names to operate remotely. If you open the Manage dialog while connected to an RT target, the dialog provides features to review the list of databases on the RT target, deploy a new database from Windows to the RT target, and undeploy a database (remove the alias and file from the RT target).

String Use

Use one of two syntax conventions for the XNET Signal I/O name string:

  • <signal>\n<dbSelection>
  • <frame>.<signal>\n<dbSelection>

Use the first syntax convention when the signal name is unique within the cluster (not used in multiple frames). This is the recommended design for signal names, because it provides a clear and simple syntax. The string contains the name of the signal, followed by a new line (\n) as a separator, followed by the selected cluster name.

Use the second syntax convention when the signal name is used in multiple frames. The string contains the name of frame, followed by a dot separator, followed by the text of the first syntax convention (signal name and selected cluster).

When you drop the I/O name onto your front panel, the control displays only one line by default. This enables the VI end user to focus on selecting the <signal>, rather than the more complex syntax that includes <dbSelection>.

Lowercase letters (a–z), uppercase letters (A–Z), numbers, and the underscore (_) are valid characters for <signal>. The space ( ), period (.), and other special characters are not supported within the signal name. The <signal> name must begin with a letter (uppercase or lowercase) or underscore, and not a number. The <signal> name is limited to 128 characters. The signal name is case sensitive.

For all supported database formats, the <signal> name is stored in the database file.

The <dbSelection> is appended to the signal name to ensure that the XNET Signal I/O name is unique. LabVIEW requires each I/O name to use a unique name, because each instance is located using its name. By appending the cluster name, NI-XNET ensures that the entire name is unique in large applications that use multiple NI-XNET interfaces (multiple clusters). The characters for <dbSelection> are the same as the name you selected using Select Database, which uses the same syntax convention as the XNET Cluster I/O name. To view the <dbSelection> when the I/O name is displayed, resize its constant/control to show multiple lines.

You can use the XNET Signal I/O name string as follows:

  • XNET Create Session (Signal In Single-Point, Signal In Waveform, Signal In XY, Signal Out Single-Point, Signal Out Waveform, Signal Out XY, Generic) VI : The single-point I/O sessions transfer the recent value for a list of signals. The waveform I/O sessions transfer signal data as LabVIEW waveforms. The XY I/O sessions transfer a sequence of values for each signal in a list. The Generic instance provides advanced features to pass in database object names as strings, including one or more signals. For all these instances, the XNET Signal I/O name is passed in as an input, but is used as a string. Within the XNET Create Session VI, NI-XNET opens the database file, reads information for the signals, and closes the database.
  • Open Refnum : LabVIEW can open the XNET Signal I/O name automatically. Wire the I/O name to a property node or VI, and the refnum is opened prior to the first use.

Refnum Use

You can use the XNET Signal I/O name refnum as follows:

  • XNET Signal Property Node : The XNET Signal property node provides information such as the signal position and size in the payload, scaling formula to physical units, and so on.