Allen-Bradley 2080-LC20-20QWB User Manual page 73

Rockwell Automation Publication 2080-UM005B-EN-E - March 2015
• Each program/POU can use up to 64 Kb of internal address space. It is
recommended that you split large programs into smaller programs to
improve code readability, simplify debugging and maintenance tasks.
• A User Defined Function Block (UDFB) can be executed within another
UDFB, with a limit of five nested UDFBs. Avoid creating UDFBs with
references to other UDFBs, as executing these UDFBs too many times may
result in a compile error.
Example of Five Nested UDFBs
UDFB1
UDFB2
• Structured Text (ST) is much more efficient and easier to use than Ladder
Logic, when used for equations. if you are used to using the RSLogix 500
CPT Compute instruction, ST combined with UDFB is a great
alternative.
As an example, for an Astronomical Clock Calculation, Structured Text
uses 40% less Instructions.
Display_Output LD:
Memory Usage (Code) : 3148 steps
Memory Usage (Data) : 3456 bytes
Display_Output ST:
Memory Usage (Code) : 1824 steps
Memory Usage (Data) : 3456 bytes
• You may encounter an Insufficient Reserved Memory error while
downloading and compiling a program over a certain size. One
workaround is to use arrays, especially if there are many variables.
Program Execution in Micro800 Chapter 6
UDFB3
UDFB4
UDFB5
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