5. SEQUENCE INSTRUCTIONS
5 − 31
MELSEC-A
Functions MC
(1) MC is master control start instruction. When the ON/OFF command for the MC
is on, operation results from MC to MCR remain unchanged.
(2) Scanning between the MC and MCR instructions is executed even when the
ON/OFF command for the MC instruction is OFF. Scan time does not therefore
become shorter.
When ON/OFF command for the MC is off, the operation result of MC to MCR is
as indicated below.
100 msec and 10 msec timers Count value becomes 0. Coil and contact turn OFF.
100 msec retentive timer and counter Coil turns OFF. Count value and contact hold present status.
Devices in the OUT instruction All turn OFF.
Devices in the SET, RST and SFT
instructions (basic and application)
Hold present status.
POINT
If an instruction which does not need a contact instruction immediately before
it (FOR to NEXT, EI, DI, etc.) is contained in the circuit in which the MC
instruction is used, the PC executes the instruction regardless of the status of
the ON/OFF command for the MC instruction.
(3) The MC instruction can use the same nesting N number repeatedly by changing
the (D) device.
(4) When the MC instruction is ON, the coil of device specified at (D) turns ON. If a
device is used twice for the OUT instruction, it is treated as a duplicate coil. To
avoid this, do not use a device specified at (D) in other instructions.
MCR
(1) This is the instruction for recovery from the master control, and indicates the
end of the master control range of operation.
(2) Do not place contact instructions before the MCR instruction.
(3) Use the MC instruction and MCR instruction of the same nesting number as a
set.
However, when the MCR instructions are nested in one place, all master
controls can be terminated with the lowest nesting (N) number.
(Refer to the "Precautions for nesting" in the program example.)
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