3. INSTRUCTION STRUCTURE
3 − 19
MELSEC-A
Cautions when a PLS instruction with Index / Startup execution instruction is used in
a FOR-NEXT.
When a device which functions as a conditions for execution of the PLS instruction /
Startup execution command starts up, the PLS command / Startup execution
instruction is executed.
M1Z SET F1Z F1Z
FOR instruction
Device No. ON/OFF state
Execution
condition
Execution/no
execution state
Device No. ON/OFF state
1st M1 ON *2 *2 F1 *2
2nd M2 ON
ON → ON
(not established)
No execution F2 OFF
3rd M3 OFF
ON → OFF
(not established)
No execution F3 OFF
4th M4 ON
OFF → ON
(established)
Execution F4 ON
REMARKS
1) *1: Execution/no execution is determined by comparing the device states between the
present states and that of one scan before/previous time.
Present device Device of one scan before/previous time
M1 M4
M2 M1
M3 M2
M4 M3
2) *2: Varies according to the M4 ON/OFF state of one scan before.
SET F1Z F1Z
M4 state of one
scan before
Execution
condition
Execution/no
execution state
Device No. ON/OFF state
OFF
OFF → ON
(established)
Execution ON
ON
ON → ON
(not established)
No execution
F1
OFF
3) *3: Device state changes in the order of M1, M2, M3 and M4 in 4 scans, and returns to M1
in the 5th scan.
*1
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