Mitsubishi Melsec-Q Series User Manual page 246

(2) Precautions for setting the extension base numbers
(a) Setting order
Set the extension base number consecutively.
In Auto mode, when any extension base number is skipped, no slots will be allocated to an empty extension
base so that the slots cannot be reserved.
For details of the base mode, refer to the follwoing.
Manuals for the CPU module used (Function Explanation, Program Fundamentals)
Main base unit
Q312B
Power supply
module
Extension base unit
Q68B
Q68B
Q68B
10 - 32
CPU 0 1 2 3
CPU module
12 13 14 15 16 17
0 0 0 0 0 0
20 21 22 23 24 25
Figure 10.32 The number of slots when a extension base number is skipped
4 5 6 7 8 9 10
Extension 1
18 19
0 0 Extension 2
Skipped
stage number
Extension 3
26 27
11
Slot number