120 Rockwell Automation Publication 1756-RM100F-EN-P - October 2018
Chapter 6 Instruction Execution
MCR Placement
The MCR instruction must be the last instruction on any rung. Otherwise, the
project generates an error upon verification.
Mitigation
N/A
Data Alignment and Memory Allocation Rules for User-defined
Data Types (UDTs) That Contain LINTs
LINT data types are aligned on 64-bit boundaries in Logix 5000™ controllers,
that use a Logix Designer project, version 27 or later. UDTs that contain
LINTs allocate memory in multiples of 8 bytes.
In 5570 and 5370 controllers that use a Logix Designer project, version 26 or
earlier, alignment and allocation used 4-byte boundaries. Proper alignment of
data improves data integrity and performance.
Language Affected
Ladder Logic (RLL) Yes
Structured Text (ST) No
Function Blocks (FBD) No
Sequential Function Chart (SFC) No
5580/5380 Controllers 5570/5370 Controllers
Project generates error on verification. No error is shown. However, it is difficult for
programmers to know how the MCR can affect any
instructions following it on the rung.
Language Affected
Ladder Logic (RLL) Yes
Struc tured Text (ST) Yes
Function Blocks (FBD) Yes
Sequential Function Chart (SFC) Yes
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