ValueAccessMode Enumeration
Enum ValueAccessMethod
Namespace: TwinCAT.Ads.ValueAccess
Assembly: TwinCAT.Ads (in TwinCAT.Ads.dll)
Version: 6.0.116+a71ced3
Syntax
C#
public enum ValueAccessMode
Members
|
|
Member name |
Value |
Description |
|---|---|---|---|
|
None |
0 |
None / Uninitialized | |
|
IndexGroupOffset |
1 |
Value access via Index Group and Offset Only | |
|
Symbolic |
2 |
Symbolic access via Instance Path only. | |
|
IndexGroupOffsetPreferred |
3 |
Uses IndexGroup IndexOffset Preferred (and Symbolic for Dereferenced Pointers / References) | |
|
Default |
2 |
The Default access mode (Symbolic) |
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. |
|
Symbolic |
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 Symbolic access. |
|
Default |
The Default-Mode setting if no other ValueAccessMode is specified. This is set to Symbolic. |