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114 Publication LOGIX-AP008B-EN-P - June 2008
Chapter 4 Conversion of Typical Program Structures
The Add-On Instruction can be called from any routine.
Note that with Add-On Instructions, you will need to create a tag of type
Add-On Instruction in a data area that is visible to the routine. This is called a
backing tag.
Before you write an Add-On Instruction, check through the Instruction Help
in RSLogix 5000 software. You might find that there is an existing instruction
that will do the job. The following section will illustrate this.
Block Copy, COP and CPS
In STEP 7, it is common to use the system function SFC20 “BLKMOV” to
copy a block of data between locations.
The instruction copies the string from the fifth location in an array of strings
to a destination string.
Often we want to copy the i-th element from an array, where “i” can vary as
the program executes. “BLKMOV” cannot do this.
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