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I/O Allocations Section 8-1
8-1-2 I/O Allocation
If I/O tables are not registered in a CJ-series CPU Unit, the CPU Unit will
automatically allocate I/O words to the Basic I/O Units that are mounted each
time the power supply is turned ON and then operation will start. This is called
automatic I/O allocation at startup (see note). This is the default setting for the
CJ-series CPU Units and it results in the allocations described in this section.
Note When using automatic I/O allocation at startup, the words allocated to Units
may disagree with the words used for them in the program if a Unit is added or
removed from the PLC. Be sure not to add or remove Units without checking
the program and be sure to always replace Units with the same type of Unit
and with the same number of I/O.
I/O Allocation to Basic I/O
Units
CJ-series Basic I/O Units are allocated words in the I/O Area (CIO 0000 to
CIO 0079) and can be mounted to the CPU Rack or Expansion Racks.
Refer to
2-4 I/O Units for more details on the available Basic I/O Units.
■ Word Allocations
Basic I/O Units on the CPU Rack
Basic I/O Units on the CPU Rack are allocated words from left to right starting
with the Unit closest to the CPU Unit. Each Unit is allocated as many words as
it requires.
Note Units that have 1 to 16 I/O points are allocated16 bits and Units that have 17
to 32 I/O points are allocated 32 bits. For example, an 8-point Unit is allocated
16 bits (1 word) and bits 00 to 07 of that word are allocated to the Unit’s 8
points.
Example 1
The following example shows the I/O allocation to 5 Basic I/O Units in the
CPU Rack.
Basic I/O Units in Expansion Racks
I/O allocation to Basic I/O Units continues from the CJ-series CPU Rack to the
CJ-series Expansion Rack connected to the CJ-series CPU Rack. Words are
allocated from left to right and each Unit is allocated as many words as it
requires, just like Units in the CJ-series CPU Rack.
CIO
0000
←
→
End Cover
10 I/O Units max.
CPU Unit
Power Supply Unit
CPU Rack
IN
16 pt
0000
IN
16 pt
0001
IN
32 pt
0002
0003
OUT
32 pt
0004
0005
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