Mitsubishi MELSEC-Q/L Programming Manual page 164

MC, MCR
Cautions when Using Nesting Architecture
(1) Nesting can be used up to 15 times (N0 to N14)
When using nesting, nests should be inserted from the lower to higher nesting number (N) with the MC instruction, and
from the higher to the lower order with the MCR instruction.
If this order is reversed, there will be no nesting architecture, and the CPU module will not be capable of performing
correct operations. For example, if nesting is designated in the order N1 to N0 by the MC instruction, and also
designated in the N1 to N0 order by the MCR instruction, the vertical bus will intersect and a correct master control
ladder will not be produced.
[Ladder as displayed in the GPP ladder mode]
A
N1 M15
N0 M16
(2) If the nesting architecture results in MCR instructions concentrated in one location, all master controls can be terminated
by use of just the lowest nesting number (N).
X1
NO M15
X2
N1 M16
X3
N2 M17
162
MC N1 M15
N1
MC N0 M16
N0
MCR N1
MCR N0
MC NO M15
NO M15
MC N1 M16
N1
MC N2 M17
N2
MCR N2
MCR N1
MCR N0
[Ladder as it actually operates]
A
M15
B
M16
X1
X2
M16
X3
M17
MC N1 M15
MC N0 M16
MCR N1
MCR N0
MC NO M15
MC N1 M16
MC N2 M17
MCR N0