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5 Understanding Programming
CJ2 CPU Unit Software User’s Manual
5-5 Symbols
5
5-5-8 Automatic Address Allocation to Symbols
When programming, you can automatically allocate addresses to symbols. Select Memory Allocation
−
Automatic Address Allocation from the PLC Menu in the CX-Programmer and then set the range
and data type for automatic allocation. With CJ2 CPU Units, addresses in the CIO Area, Auxiliary Area,
Holding Area, Work Area, DM Area, or EM Area can be allocated.
When automatically allocating symbol addresses in the EM Area, we recommend used the required
number of banks starting backward from the highest EM Area bank.
The following example shows the settings to automatically allocate symbol addresses in banks 17 and
18 hex of a CJ2H-CPU68-EIP CPU Unit (which has EM Area banks from 00 to 18 hex).
Refer to the CX-Programmer Operation Manual (Cat. No. W446) for details on the area settings for
automatic address allocation.
Additional Information
• With CJ2H CPU Units, bits in EM Area banks that are set for automatic address allocation can
be force-set/reset. Refer to 6-15 Extended Data Memory Area for the banks in which bits can
be force-set/reset.
• Automatic address allocation is not possible for structure variables.
Precautions for Safe Use
Data in the EM Area is backed up when the power supply is turned OFF or the operating mode is
changed. Be careful when using output bits specified as BOOL data. If necessary, including pro-
gramming to clear memory as required.
Example: The following instructions can be used to clear bank 18 hex to all zeros when power is
turned ON when EM Area bank 18 hex is set for automatic address allocation.
5-5-8 Automatic Address Allocation to Symbols
#0000
E18_0
E18_32767
BSET(071)
First Cycle Flag
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