ValueAccessMode Enumeration

Enum ValueAccessMethod

Namespace:  TwinCAT.ValueAccess
Assembly:  TwinCAT.Ads.Abstractions (in TwinCAT.Ads.Abstractions.dll) Version: 6.0.328+39e3229

Syntax

C#

public enum ValueAccessMode

Members

 

Member name

Value

Description

None

0

None / Uninitialized

IndexGroupOffset

1

Value access via Index Group and Offset Only

SymbolicByHandle

2

Symbolic access via Instance Path only.

IndexGroupOffsetPreferred

3

Uses IndexGroup IndexOffset Preferred (and Symbolic for Dereferenced Pointers / References)

InstancePath

4

Access by symbolic instance path.

Default

2

The Default access mode (SymbolicByHandle)

Remarks

Mode

Description

None

None/Uninitialized. No Valid mode.

IndexGroupOffset

Communicates over IndexGroup/IndexOffset only. This is the most direct/efficient access into the Process image. The advantage is that, the symbol access is done via 1 ADS round trip. Disadvantages are that not all Symbols can be accessed via IG/IO (e.g. References) and IndexOffsets could be invalid after online changes / PlcProgram downloads. Detection of these events and following invalidation of all changed symbols need to be done within the user application.

SymbolicByHandle

The Symbolic-only mode is the most safe mode to use but needs more time than the IndexGroupOffset. It could need up to 3 ADS round trips (create handle, access value, close handle) but is not influenced by online changes or / plcProgram downloads.

IndexGroupOffsetPreferred

This is a mixed access mode. For symbols, where it is possible it uses the IndexGroup/IndexOffset. For others it chooses the SymbolicByHandle access.

Default

The Default-Mode setting if no other ValueAccessMode is specified. This is set to SymbolicByHandle.

Reference

TwinCAT.ValueAccess Namespace