Mitsubishi Electric MELSEC-Q00U(J)CPU User Manual page 551

Ex.
When the index register is used as a local device
Even when program A overwrites the index register Z0 with a value of 30000, no change is made to the index
register Z0 used by program B. No error occurs as long as X10Z0 does not exceed the X device range.
Program A
Program B
Ex.
When the index register is not used as a local device
When program A overwrites the index register Z0 with a value of 30000, the value of the index register Z0 used by
program B is also changed. An error occurs when X10Z0 exceeds the X device range.
Program A
Program B
4) Use the CJ instruction.
When the CJ instruction is used as shown below and the previous condition (denoted as "(1) LD M0" in the figure
below) is off, avoid the execution of a contact instruction that uses the index register (denoted as "(2) LD X10Z0"
in the figure below). When condition (1) is off, instruction (2) is not executed and the value of the device used as a
contact is not read. Thus, the device range check processing does not detect "OPERATION ERROR" (error
code: 4101).
Note that the use of the CJ instruction increases the scan time.
(1)
(2)
Standard RAM/memory card (SRAM)
Device memory
Internal device
Z0
Program
For program A
Internal device
Z0
30000
For program B
Internal device
Z0
1000
30000
APPENDICES
A
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