Block read configuration

Use the Block Read tab to configure one or more block read groups. A block read group is a set of items for which values will be read from the field device in a single transaction. Each block read group configured within this object can be named <Block Name.>.

Note: Transaction timeouts and access paths for block read groups are inherited from the block read groups configured in the source DIObjects. The item references for each attribute are not copied. Instead item references are resolved by the Primary and Backup DIObject data sources. If aliases are used, both source DIObjects must support the same set of alias names.

Instead of the I/O points being on advise, as with a scan group, the attributes are updated once per transaction with the values from the item references. A block read transaction must be initiated from a user or script via the TransactionTrigger attribute.

In the case of a block read failure or transaction timeout, the RedundantDIObject would forcefully complete the transaction and set the data quality of incomplete items to BAD.

Click the Copy Common Block Reads button to display a dialog box that shows the block read groups configured in the Primary DIObject (shown in the Configured in primary window) and the Backup DIObject (shown in the Configured in backup window), and those block read groups shared by the two DIObjects (shown in the Identically named window). Click OK to add the block read groups in the Identically named window to the Available block reads list on the Block Read tab.

Important! Only block read groups shared by the Primary and Backup DIObjects should be configured in the RedundantDIObject. If you include non-shared groups, the RedundantDIObject will be placed in Warning state. If you configure non-shared groups in the RedundantDIObject first, you can add them to either DIObject source at a later time. You then must validate the RedundantDIObject to change it from Warning state to Good state.

To configure additional block read groups, click the Add ("+" sign) button to start filling in a new group. To delete a row from a list, select the row and then click the Delete ("X" sign) button.

To add attributes to the Associated attributes list, select a block read group and click either the Copy Attributes from Primary or Copy Attributes from Backup button. All configured attributes from the respective DIObject sources (specific to the selected Block Read) are added to the Associated attributes list.

To configure additional attributes for a block read group, use the Add ("+" sign) and Delete ("X" sign) buttons.

Valid characters for block read group and attribute names include all alphabetic characters (A-Z, a-z), and/or numeric digits (0-9), and/or the following special characters: the underscore (_), the dollar sign ($), and the pound sign (#). Spaces are not allowed.

Runtime object attributes allow you to monitor transaction errors and other diagnostic information.

Note: Although block reads are intended to be individual transactions, the actual communication with the field device is dependent on the number and type of attributes, and it may be necessary to send and receive multiple messages to and from the field device. As a result, the values exposed after a block read operation might have been obtained at different times. You must carefully design the logic in the field device to make sure that the values do not change until the full read operation is completed.

Options are as follows. For more information about the attribute associated with each option, see the attributes table in RedundantDIObject attributes.

Available block read groups:

This list contains all of the defined block read groups.

Block Read (BlockReadList attribute)

The list of names of all configured block read groups. When a set is made with new values, it should contain a unique name for the block read group, from which data will be received. Group names should be unique across ScanGroupList, BlockReadList, and BlockWriteList.

Associated attributes for <block read group name>:

This list contains all of the attributes that are configured for the selected block read group.

Attribute (<Block Name.>ItemList attribute)

The tag name of an item in the field device.