I/O String Data Point Tag

Help Contents

Introduction

The I/O String Data Point Tag String Data Point Tag Icon maps a variable length string to an external data source.

Configuration Properties

The I/O String Data Point Tag supports the configuration properties of the String Data Point Tag plus these properties:

Property Type Version Description
AllowControls BOOL 3.12 Whether Fernhill SCADA can send controls from this tag to the data source.
IODataSource Reference 3.12 A reference to another tag that provides the external data for the tag.
IOItemName WSTRING 3.12 The data item within the external data source.
MaxSizeHint UDINT 4.6 For strings stored in registers, the maximum number of bytes to read. For more information see MaxSizeHint Property below.
OutOfService BOOL 3.92 Whether retrieval of data from the external data source is suspended for this data point tag. For more information see OutOfService Property below.

AllowControls Property

The AllowControls property controls access to the WriteValue Tag Command.

When AllowControls is FALSE, access to the WriteValue Tag Command is blocked. This prevents any user, or program, sending control requests to the data source from this tag. The default value is FALSE to follow security best practice of deny by default.

Even when AllowControls is TRUE, an operator requires the Write User Privilege to send controls to the data source.

For an operator to send a control to the data source, both of these conditions must be true:

IODataSource and IOItemName Properties

The IODataSource and IOItemName properties define which data item the I/O String Data Point Tag is associated with:

To configure these properties:

  1. Click the browse button ... of the IODataSource property and choose the data source.
  2. Click the browse button ... of the IOItemName property.

    Note: The format of the IOItemName property depends on the type of data source chosen.

To understand how the IOItemName property is formatted, see Data Address Format.

MaxSizeHint Property

The MaxSizeHint property is used only when the IOItemName property refers to one of these tag types:

This property tells the driver the maximum number of bytes to read when reading a string value.

For more information see Register String Format.

OutOfService Property

Use the OutOfService property to suspend retrieval of data from the external data source.

For normal operation, OutOfService should be set to False. If a data source is providing faulty data, it might be appropriate to set OutOfService to True.

Data Properties

The I/O String Data Point Tag supports the data properties of the String Data Point Tag.

Tag Commands

The I/O String Data Point Tag supports tag commands of the String Data Point Tag plus these tag commands:

Tag Command Version Description
WriteValue 3.12 Writes a new value to the data source via the I/O tag.

Relationships to Other Tag Types

The I/O String Data Point Tag builds on the features of these tag types:

Further Information

String Data Point Tag

To learn about properties common to all String Tags.

Core Driver

To learn about the Core Data Driver.

Glossary

For the meaning of terms used in Fernhill SCADA.