Rockwell Automation Publication 2080-UM002M-EN-E - April 2022 137
Chapter 7 Program Execution in Micro800
user-defined variables, data memory also includes any constants and
temporary variables generated by the compiler at build time.
If your project is larger, it affects the power up time. Typical power up time is
10...15 seconds for all controllers. However, if your project has a lot of initial
and project values, it may cause the power up time to exceed 30 seconds. After
boot up, EtherNet/IP connections may take up to 60 seconds to establish.
The Micro800 controllers also have project memory, which stores a copy of the
entire downloaded project (including comments), as well as configuration
memory for storing plug-in setup information, and so on.
Guidelines and Limitations
for Advanced Users
Here are some guidelines and limitations to consider when programming a
Micro800 controller using Connected Components Workbench software:
• Each program/POU can use up to 64 Kb of internal address space. For all
controllers except Micro870, it is recommended that you split large
programs into smaller programs to improve code readability, simplify
debugging and maintenance tasks.
• A User Defined Function (UDF) uses significantly less memory than a
User Defined Function Block (UDFB). For example, 30% less for a typical
sized program compared to a UDFB with one instance. The savings
increases as the number of UDFB instances increases.
• 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. This also applies to UDFs.
Example of Five Nested UDFBs
• 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, a great alternative is to use ST
combined with either UDF or UDFB.
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.
UDFB1
UDFB2
UDFB3
UDFB4
UDFB5
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