Allen-Bradley 1756-CNB User Manual page 77

Action
2. Delete unused tags.
3. Use arrays and user-defined data types
instead of individual tags.
Details
This reduces the size of the tag database. A smaller database takes less time to crossload.
To delete unused tags:
A. Open one of the tags folders.
B. Click Edit Tags.
C. From the Show list, select Unused.
D. From the Edit menu, choose Select All.
E. Press the Delete key.
When you create a tag, the controller always sets aside at least 4 bytes (32 bits) of
memory. The controller does this even if the tag needs only 1 bit.
When you create an array or a user-defined data type, the controller packs smaller data
types into 4-byte (32-bit) words. This means the controller has less data to crossload.
This array of 32 BOOLs takes only 4-bytes.
The controller crossloads only 4 bytes.
These 3 BOOL tags take 12 bytes total (3 tags x 4 bytes/tag = 12 bytes).
The controller crossloads all 12 bytes.
Arrays and user-defined data types help you the most with BOOL tags. But also use them
for your SINT, INT, DINT, REAL, COUNTER, and TIMER tags.
Configure and Program the Controller
Publication 1756-UM523F-EN-P - December 2006
77