I/O Digital Data Point Tag

Introduction

The I/O Digital Data Point Tag maps digital tag with two states to an external data source.

Use caution when using an I/O Digital Data Point Tag to write a bit to a word register with these drivers:

Mitsubishi Melsec Driver
Modbus Driver (where command 22 is not supported)

The PLC Devices supported by these drivers do not support bit writes to word registers. To work around this restriction, Fernhill SCADA uses a three step process to set or clear the bit:

The word register containing the bit is read from the PLC.
The required bit is set or cleared.
The word register is written back to the PLC.

If you are using Fernhill SCADA to write a bit to a word register in these PLC types make sure that:

The PLC program does not write to the word register.
Any other agent does not write to the word register.

Configuration Properties

The I/O Digital Data Point Tag supports the configuration properties of the Digital 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.
InputDelay	TIME	3.87	The minimum time before a change to the input signal is detected. Use this property to suppress a noisy signal. Notes: The actual value used for the input delay is rounded up to a multiple of the tag scan interval. InputDelay is not supported data point tags associated with a DNP3 Outstation.
OutOfService	BOOL	3.92	Whether retrieval of data from the external data source is suspended for this data point tag.
RawValueInvert	BOOL	3.12	Whether the raw value is inverted with respect to the tag state.

AllowControls

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:

The AllowControls property is TRUE.
The operator has the Write User Privilege.

IODataSource and IOItemName

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

The IODataSource property sets the data source for the tag.
The IOItemName property sets the "Address" of the data within the data source.

To configure these properties:

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

OutOfService

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

When OutOfService is False, data from the external data source is retrieved normally.
When OutOfService is True, retrieval of data is suspended and the data point tag quality is set to "Out of Service".

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.

RawValueInvert

The RawValueInvert property configures whether the raw I/O value is inverted with respect to the tag value. When enabled, the inversion applies both to data read from the I/O device and also to controls to the I/O device.

Data Properties

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

Tag Commands

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

Further Information

Digital Data Point Tag

To learn about properties common to all digital tags.

Core Data Driver

To learn about the Core Driver.

Glossary

For the meaning of terms used in Fernhill SCADA.