Memory Allocation; Guidelines And Limitations For Advanced Users - Allen-Bradley Micro830 Manual

Memory Allocation

Guidelines and Limitations
for Advanced Users
Rockwell Automation Publication 2080-UM002K-EN-E - March 2019
Depending on base size, available memory on Micro800 controllers are shown in
the table below.
Memory Allocation for Micro800 Controllers
Attribute 10/16-poin
(Micro830)
(1)
Program steps 4 K
Data bytes 8 KB
(1) Estimated Program and Data size are "typical" – program steps and variables are created dynamically.
1 Program Step = 12 data bytes.
These specifications for instruction and data size are typical numbers. When a
project is created for Micro800, memory is dynamically allocated as either
program or data memory at build time. This means that program size can exceed
the published specifications if data size is sacrificed and vice versa. This flexibility
allows maximum usage of execution memory. In addition to the 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.
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.
Program Execution in Micro800 Chapter 6
20-point 24- and 48-points
(Micro820) (Mico830, Micro850)
10 K 10 K
20 KB 20 KB
24-point
(Micro870)
20 K
40 KB
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