ControlLogix Protocol Modes

• Logical Blocking makes a call to read the whole structure as one block of memory. 
• Logical Non-Blocking reads sub-structures as one block of memory. 
• Symbolic reads tags based on tag names (i.e. the CIP protocol).

In general…

Symbolic Mode is Most efficient when only a few tags are being read.

Logical Blocking Mode can either help or hurt, depending on the number of tags you are accessing within a structure in RSLogix. This mode will pull the entire structure into the driver, and allow the driver to parse the tag addresses internally. If you are referencing only a few tags within a structure, this would be inefficient. If the arrays you are accessing are all within a structure and make up most of the tags within that structure, this option would improve your performance.

Logical Non-Blocking is usually the most efficient method of communications. If you’re accessing less than 30 percent of the tags within a structure, this is the recommended method.