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MELSEC-Q
4 SEQUENCE PROGRAM CONFIGURATION AND EXECUTION
CONDITIONS
(5) Program creation restrictions
(a) A device which is switched ON by a PLS instruction in an interrupt program
will remain ON until that interrupt program is executed again.
X0
OFF
ON
M0
OFF
ON
END 0
IO
IRET END 0 END 0 IO IRET END 0
PLS M0
X0
PLS M0
X0
Switched OFF by PLS M0 instruction
Switched ON by PLS M0 instruction at X0 leading edge (OFF to ON)
(b) A DI status (interruption prohibited) is established during execution of an
interrupt program.
Do not execute EI/DI instructions in the interrupt program.
(c) Timers cannot be used in interrupt programs.
As timers are used at OUT T
instructions to update present values and
switch contacts ON and OFF, the use of a timer in the interrupt program
would make a normal time count impossible.
(d) The following commands cannot be used in the interrupt program.
• COM
• ZCOM
• EI
• DI
(e) When the interrupt program/fixed scan execution type program is executed
at a measuring time such as the scan time or execution time, the values of
the interrupt program/fixed scan execution type program are added to the
measured time.
Thus, if the interrupt program/ fixed scan execution type program is
executed, the values stored in the following special registers and
GX Developer monitor values will be longer than when the interrupt
program/ fixed scan execution type program is not executed.
1) Special registers
• SD520, SD521: Current scan time
• SD522, SD523: Initial scan time
• SD524, SD525: Minimum scan time
• SD526, SD527: Maximum scan time
• SD528, SD529: Current scan time for low speed
• SD532, SD533: Minimum scan time for low speed
• SD534, SD535: Maximum scan time for low speed
• SD540, SD541: END processing time
• SD542, SD543: Constant scan wait time
• SD544, SD545: Cumulative execution time for low speed execution
type programs
• SD546, SD547: Execution time for low speed execution type
programs
• SD548, SD549: Scan program execution time
• SD551, SD552: Service interval time
2) GX Developer monitor values
• Execution time measurement
• Scan time measurement
• Constant scan
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