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Allocating First Words to Racks Section 8-4
Precautions in Setting First Slot Words
When the I/O tables are edited, the CX-Programmer checks for any duplica-
tions in word allocations caused by first word settings. It is conceivable, how-
ever, that duplications in word allocations could occur after the I/O tables have
been registered, e.g., as the result of replacing a 1-word Unit with a 2-word
Unit. In this case the extra word needed by the new Unit would still also be
allocated to the next Unit.
When the PLC is turned ON, the CPU Unit checks the registered I/O tables
against the actual Units mounted to the PLC. If there are any duplications, and
error will occur and it will be no longer possible to edit the I/O tables. If this
happens, the I/O tables will have to be deleted and recreated or retransferred
from a Programming Devices.
8-4 Allocating First Words to Racks
In the CJ-series PLCs, the first word allocated to each Rack can be set with
the CX-Programmer’s I/O table edit operation. For example, the CPU Rack
can be set to be allocated words starting with CIO 0000; the next Rack, words
starting with CIO 0100; the next Rack, words starting with CIO 0200; etc. This
can make it easier to check word allocations to Units without calculating all the
way from the CPU Rack.
Note The first words for Racks cannot be set at the same time as the first words for
slots.
Word Allocations
For Racks in which the first word address has been set, words are allocated to
Units in the order that the Units are mounted (from left to right) beginning with
the specified first word. Words are not allocated to empty slots.
For Racks in which the first word address has not been set, words are allo-
cated in rack-number order (lowest to highest) continuing from the last word
allocated to the previous rack and starting with CIO 0000 on the first Rack for
which the first word is not set.
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