Analog Output Tag Type Properties: I/O Tab
The I/O Tab holds the properties used to identify and establish a connection to the communication driver tag being used to exchange data with your physical I/O device (e.g. PLC or RTU). This is accomplished by identifying the communication driver tag that communicates with the physical I/O device, the address at the physical I/O device from which this tag is to read its data, and the rate at which the I/O device should be scanned for data.
(Click title to expand text)
Select the communication driver tag to which data will be written.
The tag button to the right of the field opens the tag browser, from which you can either select an existing communication driver tag or add a new one. The X button will clear the field. Right-clicking on a tag in the field will open a dialog from which you can the driver`s properties.
Provide the address within I/O device to which this tag is to write data. This value must match the configuration of your PLC or RTU hardware.
The addressing system for each of the drivers that come with VTS is provided in the Communication Driver Tags section of this guide.
Provide units of measure that the input data represents. Possible values for this field include "rpm" "degrees C", "%", etc.
(found in output and control tags)
The Data Source property enables you to identify a tag that will set the value of this output tag (rather than this tag obtaining its value exclusively from user input). A change in the data source tag's value (and thus this tag's value) will result in a value being written to the I/O device. The data source tag can be an alarm tag to perform setpoint control, a calculation tag to perform logic, or an analog or digital tag to copy data from one I/O device to another.
For a pulsed digital output, the change in state of the value from a 0 to a 1 will cause the configured pulse to be written to the I/O device.
If a valid tag is referenced in the Data Source field and, a user-controllable drawing method is supplied on screen, then the value will be set by whichever has changed most recently.
The Data Source field can be used to associate this tag with a new or
existing tag using the tag browser button. The 
button opens the Tag Browser, which
displays only the existing I/O, calculation, or alarm tags that can be data
sources for this tag, and enables you to create a new tag of these types using
its New button. (Information on using the Tag Browser can be found in
"
The Data Source field can be cleared using the X button that appears to its right.
Right-clicking a tag selected in the Data Source field opens the tag properties folder related to the selected tag.
The value output by an analog control can be supplied by an operator via a drawing method on the screen, it can be supplied by a data source, or both can be used.
Normally, the data source would be another tag or an expression. If both a data source and an operator control are provided, then the value of the control tag will be whichever value was most recently set.
Write output when Data Source changes / Use Data Source for display only
The data source can be used either as the value of the tag, updating the tag's value whenever the data source changes, or it can be used for display purposes only, leaving the value output by the tag unchanged. These two radio buttons allow you to select one mode or the other.