Configurable ControlLogix Protocol Modes for Optimal Performance

General Guidelines for Selecting Logix Protocol Mode in TOP Server

Selecting the right protocol mode when using the TOP Server ControlLogix Ethernet driver is dependent on certain aspects of your project and what data you need to retrieve from your controller.

• Symbolic Mode - Most efficient when only a few tags are being read - this mode packs the entire ASCII symbol tag name in the request so tag name length is a limiting factor. This mode is recommended for best performance over telemetry networks such as cell modems/radios.
  
  
• Logical Non-Blocking Mode - Generally speaking, this is the most efficient mode. If you are accessing less than 30 percent of the tags within a structure, this is the recommended method.
  
  
• Logical Blocking Mode - This mode is most efficient when you need to access the majority of tag members within a structure since it pulls the entire structure into the driver, and allows the driver to parse the tag addresses internally.

Logical Non-Blocking Mode Details (Default)

Logical Non-Blocking mode is identical to symbolic in that all Logix tags are requested individually, utilizing the Multi-Tag Request Packet. They differ in that the Client/Server tags are specified in the packet with their physical address, not their symbolic address.

Because the physical pointer for a Logix tag is so much smaller than a symbolic tag name, more addresses can be returned in a single roundtrip request, making this logical non-blocking mode considerably faster than symbolic mode.

Logix Protocol Mode Support by Firmware Revision

The TOP Server ControlLogix Ethernet driver queries the controller when initializing communications to determine key information about the controller, including the version of firmware currently installed.

As such, for logical/physical modes, the driver can intelligently select the proper protocol to be used based on the confirmed firmware revision and what it supports.