# About the Device data source

A tag with Device as its data source receives its data from a source external to FactoryTalk View, that is, a programmable controller via RSLinx or from a third party OPC server, or another Windows program through an OPC server.

When you define the tag, you specify the address of the value in the programmable controller's data table, or its OPC item. The system then scans this location, and stores the value in the value table, making it available to the rest of the system.

## To set up Device as the data source

1. In the Tag Database editor's form, under Data Source, choose Device.
2. Type an address or click the Browse button (...) beside the Address box to open the Tag Browser and select a tag address.

## Option

- Address

  This is the physical address in the programmable controller or the OPC item that this tag is associated with. For non-OPC tags, the address syntax depends on the programmable controller's addressing convention. The maximum length is 255 characters.

  Important: | Do not point an analog HMI tag to a Boolean device tag and also do not point a digital HMI tag to a non-Boolean device tag.

Tip: | It is vital that address referenced in SLC controllers actually exist in the SLC data table. Referencing invalid SLC addresses will cause valid addresses to fail. Do not use leading zeroes in tag addresses. FactoryTalk Linx interprets a leading zero to mean an octal notation.

## See also

Set up OPC communications

About HMI tag types

About data sources

data source

Value table