R/W items in diagnostics

The R/W Status column appears in the details pane for the Structure, Transactions, Messages, and Device Groups nodes.

It shows any pending read/write status as follows:

• Any item that has been updated with VTQ (good or bad) is marked R. Before being updated with VTQ, it is marked with a hyphen (-) for read-uninitialized.

• Any item that has no pending write operations, because it either contains all completed write activities or has never been poked, is marked W. If write operations are pending on an item, it is marked with a -W.

The normal state of an item is R/W. All others reflect temporary or special states, such as an item being in an initialization state, an item is processing a write, or an error accessing item data occurred.

1. In the Structure dialog box, an R indicates:

   • The item is updated from any subscription or transaction with a corresponding fully qualified itemID at least once.

   • A VTQ for any client group item pointing to this item is available if the item is reading from cache and the item is active.

     The R is missing only for a short period of time during initialization of an active item. Reasons for a missing an R state include:

   • Item is not active long enough to acquire data.

   • Item cannot access data.

   • System item $SYS$PollNow is poked and the device item is not updated yet.

     In the Structure dialog box, a W indicates:

   • No pokes are pending on this item.

   • All pokes are complete.

   • No write transaction items are connected to this item.

2. In the Transaction dialog box, demand reading or demand writing creates a new transaction item. Each transaction item represents a unique demand operation on this item. Transaction items display R in the R/W Status column during read transactions and W during write transactions. The R indicates that the item’s VTQ was acquired in this transaction for this item, and W indicates that the item poke is complete. R also can represent a refresh or property read. A refresh is typically a device group-wide read (either from the field device or from cache) that is triggered by the client. A property read is a read of any property of an item (usually a property other than VTQ) by the client.

3. In the Message dialog box, an R indicates that item VTQ was acquired for this item and a W indicates that the item poke is complete.

4. In the Device Groups dialog box, an R indicates that the item VTQ was acquired for this item. W is always set because there are no transaction items and a poke is always complete.