Mitsubishi Electric melsec q00ujcpu User Manual page 374

1) Precautions for resetting the counter
Execution of the RST C
If the execution condition for the OUT C
instruction, turn on the coil of C
value (count value + 1).
[Ladder example]
Figure 9.32 Counter resetting ladder example
In the above ladder example, when M0 turns on from off, the coil of C0 turns on, updating the
current value.
When C0 reaches the preset value finally, the contact of C0 turns on, and execution of the RST C0
instruction clears the current value of C0. At this time, the coil of C0 also turns off.
If M0 is still on in the next scan, the current value is updated since the coil of C0 turns on from off
at execution of the OUT C0 instruction. (The current value is changed to 1.)
END
Sequence
program
ON
M0 OFF
Coil of C0
OFF
Current value
update, turning on
the contact
RST C0 OFF
Count value cleared, the contact turned off
To prevent the above, it is recommended to add a normally closed contact of the OUT C0
instruction execution to the condition for the RST C0 instruction execution so that the coil of C0
does not turn off while the execution condition (M0) of the OUT C0 instruction is on.
[Modified ladder example]
Figure 9.34 Counter resetting ladder example (recommended)
instruction also turns off the coil of C .
instruction is still ON after execution of the RST C
at execution of the OUT C
M0
C0
END
OUT C0 RST C0
ON
Turning off the
coil of C0
Figure 9.33 Current value update timing
M0
C0 M0
instruction and update the current
K10
C0
RST C0
END
OUT C0 RST C0
Current value is
updated since the coil
of C0 turns on from off.
K10
C0
RST C0
CHAPTER9 DEVICES
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