PLC Device Tag

Introduction

The PLC Device Tag PLC Device Tag Icon represents a logical link to a PLC device or other type of SCADA/HMI data source.

Configuration Properties

The PLC Device Tag supports the configuration properties of the Alarm Tag, plus these additional configuration properties:

Property Type Version Description
AlarmSeverity UINT 1.5 The severity of the alarm raised when the PLC device fails.
EnableDirectWrite UINT 2.3 Whether data can be written directly to the PLC device.
PollInterval TIME 2.2 The interval between each device status poll. See Interval and Offset for information on how Intervals and Offsets define the time of activities.
PollOffset TIME 2.2 The offset added to the PollInterval to get the actual status poll time. See Interval and Offset for information on how Intervals and Offsets define the time of activities.
TagScanInterval TIME 3.15 The interval between each scan of the IO Data Tags directly associated with the PLC. See Interval and Offset for information on how Intervals and Offsets define the time of activities.
TagScanOffset TIME 3.15 The offset added to the TagScanInterval to get the actual tag scan time. See Interval and Offset for information on how Intervals and Offsets define the time of activities.

EnableDirectWrite Property

The EnableDirectWrite configuration property controls access to these tag commands:

Note: A PLC tag typically supports either DirectWriteByte or DirectWriteWord, but not both.

When EnableDirectWrite is FALSE access to the DirectWriteXXX tag commands is blocked. This prevents any user, or program, sending direct write requests to the PLC from this tag.

When EnableDirectWrite is TRUE access to the DirectWriteXXX tag commands is allowed. A user, or program, can send write requests to the PLC from this tag if the user, or program, has the Direct Write User Privilege.

PollInterval and PollOffset Properties

The PollInterval and PollOffset properties control how often the driver queries the status of the PLC Device. The result of the status poll is used to determine whether the PLC device is offline or online.

See Interval and Offset for information on how to configure scheduled activities.

Dynamic Properties

The PLC Device Tag supports all of the dynamic properties of the Core Tag, plus these additional dynamic properties:

Property Type Version Description
State UINT 1.0 The state of the device
StateDescription WSTRING 1.0 The text description of the device state
ModelName WSTRING 1.9 The detected model name of the target device
PollTimer TimerStatus 2.4 The status of the poll timer
TagScanTimer TimerStatus 3.15 The status of the tag scan timer

The State property can have these values:

StateDescription
0Initial state before the driver starts
1The channel reference is invalid
2The device is not responding
3The channel hosting the device is offline
4The reply from the device is not in a recognized format
5The device responded with an error code
6The channel for this device is disconnected or failed
7This device is trying to use a channel that is exclusively allocated to another device
8The device is offline
9A configuration error prevents operation
15The device is online and communicating

Tag Commands

The PLC Device Tag supports the tag commands of the Alarm Tag.

Relationships to Other Tag Types

The PLC Device Tag builds on the features of these tag types:

The PLC Device Tag is used as a building block for these tag types:

Further Information

Core Tag

To learn about properties common to all tags.

Alarm Handling

To learn about alarm management.

Glossary

For definitions of the terms used in Fernhill SCADA.