Internal String Data Point Tag

Introduction

The Internal String Data Point Tag stores a variable length string value internally in the Fernhill SCADA Server.

The Internal String Data Point Tag is a license free tag. You can create any number of these tags without restriction.

The Internal String Data Point Tag supports the configuration properties of the String Data Point Tag plus these properties:

Property	Type	Version	Description
ApplyInitialValue	USINT	3.13	Defines when the initial value should be applied to the tag. Options are: 0 = Never, 1 = If no value written, 2 = On server restart.
InitialValue	WSTRING	3.13	The initial value of the tag.
ShowWriteValue	BOOL	3.34	Whether to show the WriteValue Tag Command in the Standard Tag Menu.
ShowWriteValueQuality	BOOL	3.34	Whether to show the WriteValueQuality Tag Command in the Standard Tag Menu.

The ApplyInitialValue property defines when the InitialValue property is applied to the tag. The options are:

ApplyInitialValue	Rules
Never	The InitialValue property is ignored. New tags created by copying an existing tag will be initialized with an empty string and bad quality. If the Fernhill SCADA Server is restarted, the value of the tag is preserved.
If no value written	If there has been no "Data Write" to the tag, the tag gets its value from the InitialValue property. Changes to the InitialValue property will update the value of the tag until the first "Data Write". After the first "Data Write", changes to the InitialValue property have no effect. New tags created by copying an existing tag will be initialized with the InitialValue property and good quality. If the Fernhill SCADA Server is restarted, rules 1 to 3 apply.
On server start	If there has been no "Data Write" to the tag, the tag gets its value from the InitialValue property. Changes to the InitialValue property will update the value of the tag until the first "Data Write". After the first "Data Write", changes to the InitialValue property have no effect. New tags created by copying an existing tag will be initialized with the InitialValue property and good quality. If the Fernhill SCADA Server is restarted, the tag is reset to the InitialValue property.

Note: In the above table, a "Data Write" includes:

A WriteValue tag command from the standard tag menu, a logic program, an operator action, or API.
A WriteValueQuality tag command from the standard tag menu, a logic program, an operator action, or API.
An assignment to the tag in a Program Tag.

The Internal String Data Point Tag supports the dynamic properties of the String Data Point Tag.

The Internal String Data Point Tag supports tag commands of the String Data Point Tag plus these tag commands:

Tag Command	Version	Description
WriteValue	1.2	Writes a new value to the tag.
WriteValueQuality	1.2	Writes a new value and quality to the tag.

The Internal String Data Point Tag builds on the features of these tag types:

To learn about properties common to all String Tags.

To learn about the Core Data Driver.

For the meaning of terms used in Fernhill SCADA.