Mitsubishi MELSEC QS Series Programming Manual page 93

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 safety 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 displayed in the GX Developer
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
N0 M15
X2
N1 M16
X3
N2 M17
[Ladder of actual operation]
MC N1 M15
N1
MC N0 M16
N0
MCR N1
MCR N0
MC N0 M15
N0
MC N1 M16
N1
MC N2 M17
N2
MCR N2
MCR N1
MCR N0
5.4 Master Control Instructions
5.4.1 Setting and resetting the master control (MC, MCR)
A
M15
B
M16
X1
M15
X2
M16
X3
M17
MC, MCR
MC N1 M15
MC N0 M16
MCR N1
5
MCR N0
MC N0 M15
MC N1 M16
MC N2 M17
MCR N0
5-41