Specifications

Allen-Bradley ControlLogix Ethernet Driver Help
Benefits Detriments
1. Contents are retrieved on every
read.
2. Low device turnaround time
because the client/server tags
are specified in the packet with
the logical address.
3. Contains the maximum request
per multi-request packet because
each request is a fixed size.
1. Initialization overhead when uploading the project to
determine the logical addresses.
2. If the minority of Logix tags are referenced, it is slower
than Logical Non-Blocking Mode (because more data is
being accessed from the PLC than referenced in the
client/server tags).
Note: This mode is preferred when the majority of Structure tag members are referenced by a client/server.
See Also: Performance Statistics and Tuning
Symbol Instance vs. Physical Protocol
Symbol Instance reads are CIP requests wherein the CIP Instance ID is used to specify a Native tag in a read
request. In Non-Blocking Mode, the CIP Member ID may be required to fully qualify the path to structure
members and array elements. For example, the CIP Instance ID would represent the structure whereas the CIP
Member ID represents the member within the structure. Because of the addition of CIP Member IDs required to
fully qualify a client/server tag, requests can vary in size. The deeper the nesting of structures, the more CIP
Member IDS required to specify it and the fewer requests that fit in a single packet. Symbol Instance reads were
introduced in FRN V21.
Physical reads are CIP requests wherein the DMA address is used to specify a Native tag in a read request. In
Non-Blocking Mode, the byte offset may be required to fully qualify the path to structure members and array
element. For example, the starting DMA address would represent the structure whereas the byte offset
represents the member within the structure. Ultimately the start + offset is the DMA address specified in the
request: all requests are fixed in size (unlike Symbol Instance reads). No matter how deep structures are nested,
the request is the same size in the packet. Physical reads have been deprecated as of FRN V21.
Detecting a Change in the Controller Project
The Allen-Bradley ControlLogix Ethernet Driver monitors for project changes and can detect downloads in
progress, online edits, and offline edits. When the protocol is set to Logical, users have the option to synchronize
the driver's project image with that of the controller project. Synchronization ensures that the driver uses the
current logical address for each Native tag when performing reads and writes.
l Downloads in Progress: The driver monitors for both online and offline edits in every request. It detects
if a download occurs while actively reading or writing to Native tags, then follows a project-change
procedure depending on its mode. To enable this synchronization, right-click on the device and select
Properties. In the Logix Options tab, locate either Online Edits or Offline Edits and select Yes.
l Online Edits: The driver monitors for online edits in every request. It detects if an online edit occurs with
the controller on the following read or write operation, then follows a project-change procedure
depending on its mode. To enable this synchronization, right-click on the device and select Properties.
In the Logix Options tab, locate Online Edits and select Yes.
l Offline Edits:The driver monitors for offline edits in every request. It detects if an offline edit occurs
with the controller on the following read or write operation, then follows a project-change procedure
depending on its mode. To enable this synchronization, right-click on the device and select Properties.
In the Logix Options tab, locate Offline Edits and select Yes.
Project Change Procedure (Symbolic Mode)
1. A project change is detected.
2. A message is posted to the Event Log indicating that a change is detected.
3. During project change, the scenario for downloads is as follows:
www. kepware.com
121