Mitsubishi MELSEC QS Series Programming Manual page 45

(2) SET/RST instructions using the same device
(a) The SET instruction turns ON the specified device when the execution command is ON
and performs nothing when the execution command is OFF.
For this reason, when SET instructions using the same device are executed two or
more times in one scan, the specified device will be ON if any one of the execution
commands is ON.
(b) The RST instruction turns OFF the specified device when the execution command is
ON and performs nothing when the execution command is OFF.
For this reason, when RST instructions using the same device are executed two or
more times in one scan, the specified device will be OFF if any one of the execution
commands is ON.
(c) When the SET instruction and RST instruction using the same device are programmed
in one scan, the SET instruction turns ON the specified device when the SET execution
command is ON and the RST instruction turns OFF the specified device when the RST
execution command is ON.
When both the SET and RST execution commands are OFF, the ON/OFF status of the
specified device will not be changed.
[Circuit]
X0
X1
[Timing Chart]
END
ON
OFF
X0
X1
OFF
OFF
M0
When specifying output (Y) in SET/RST instruction, the ON/OFF status of the device at the
execution of the last instruction in the scan is returned as the output (Y).
3.7 Operation when OUT, SET/RST, or PLS/PLF Instructions Use the Same Device
SET M0
RST M0
X0
SET M0
X1
RST
END
ON
ON
RST M0 is not executed
because X1 is OFF.
(M0 remains ON.)
M0 is turned ON
because X0 is ON.
X0
SET
X1
M0
END
M0 is turned
OFF because X1 is ON.
SET M0 is not executed
because X0 is OFF.
(M0 remains ON.)
3
M0
RST M0
3-15