Mitsubishi Electric MELSEC iQ-R Series - Data Used by Process Control Instructions

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11 PROCESS CONTROL INSTRUCTIONS
11.1 Overview
Data used by process control instructions
The data used by process control instructions includes the following.
• Loop memory (Page 1186 Loop memory)
• Input data (Page 1187 Input data)
• Block memory (Page 1187 Block memory)
• Operation constant (Page 1188 Operation constant)
• Local work memory (Page 1188 Local work memory)
Loop memory
The loop memory is an area in which the data used commonly by the process control instructions specified by the loop type is
stored. The loop memory has also another area in which the data used by the CPU module system during execution of
process control instructions is stored.
The loop memory consists of loop tag memory and loop tag past value memory.
• Page 1186 Loop tag memory
• Page 1186 Loop tag past value memory
The loop memory is configured with 128 words, and therefore a device which has 128 consecutive words
should be specified when the loop memory area is allocated.
■Loop tag memory
The loop tag memory is an area (96 words) in which the control information used commonly by the process control
instructions specified by a loop type among the basic loop types ( Page 1181 Basic loop types) is stored.
For the applications of the area used by process control instructions in the loop tag memory, refer to the
following.
Page 2082 List of Loop Tag Memory Areas Used by Process Control Instructions
■Loop tag past value memory
The loop tag past value memory is an area (32 words) used by the system during execution of process control instructions. No
data can be written during operation. If data is written to the loop tag past value memory during operation, normal operation is
disabled.
When starting a process control instruction, write 0 to the loop tag past value memory.
+96
+127
+0
+95
... ...
Loop memory
Loop tag memory
Specified device number
96 words
32 words
Loop tag past value memory
(system use only)