Buffered data run-time behavior

Scan Group

When the buffer property of a scan group’s dynamic attribute is subscribed to at run time, the buffer data support is enabled. The scan group accumulates all of that item's updates into a buffer of VTQs.

The scan group supports buffering up to 10,000 VTQs per item per scan. Higher data throughput rates are not supported

On Scan

When the object is placed On Scan, the system enables all available items and resets item error count.

Off Scan

When the Scan Group goes Off Scan, it will clear all buffers associated with each item in the Scan Group.

When buffered data is enabled and the host object goes Off Scan, a VTQ with Bad Quality is added to the buffer. On a subsequent scan, the buffer property of the Value attribute is cleared.

Inputs

On Startup

When buffer is enabled on the attribute, buffer support for the input is enabled. No data is processed during this phase.

Execute

The buffered attribute is registered, but no data is processed or stored until the buffer reference finishes initializing.

Shutdown

Interfaces are unregistered. (No change in behavior for buffered data-enabled.)

Redundancy

Application Engine

Buffered attributes are not synchronized with a redundant partner. When a failover occurs, unprocessed buffered data is lost.

Redundant DIObject

When buffering is enabled, the RedundantDIObject (RDI) subscribes to the buffer property of its DI source items.

On failover, all advised items are moved to the backup node, whether or not buffered data is enabled.

Buffered attributes are not synchronized with a redundant partner. When a failover occurs, unprocessed buffered data is lost.