Allen-Bradley MicroLogix 1400 Instruction Manual page 96

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94 Programming Instructions Overview
Publication 1766-RM001A-EN-P - October 2008
Indirect Addressing
Indirect addressing allows components within the address to be used as
pointers to other data locations within the controller. This functionality
can be especially useful for certain types of applications, recipe
management, batch processing and many others. Indirect addressing can
also be difficult to understand and troubleshoot. It is recommended that
you only use indirect addressing when it is required by the application
being developed.
The MicroLogix 1400 supports indirection (indirect addressing) for Files,
Words and Bits. To define which components of an address are to be
indirected, a closed bracket "[ ]" is used. The following examples illustrate
how to use indirect addressing.
Indirect Addressing of a Word
B3:0
0000
0
• Address: N7:[N10:1]
• In this example, the element number to be used for source A in the
ADD instruction is defined by the number located in N10:1. If the
value of location N10:1 = 15, the ADD instruction operates as
"N7:15 + Source B".
• In this example, the element specified by N10:1 must be between 0
and 255, because all data files have a maximum individual size of
256 elements.
If a number larger than the number of elements in the data file is
TIP
placed in N10:1 (in this example), data integrity cannot be
guaranteed, because a file boundary will be crossed. This may not
generate a controller fault, but the data location is invalid/unknown.
Indirect Addressing of a File
LIM LIM
Limit Test
0001
Low Lim
Test
High Lim
ADD ADD
Add
Source A N7:[N10:1]
Source B
Dest
B3:0 COP COP
Copy File
10 0 Source #N[N50:100]:10
10< Dest
N50:100 Length
10<
25
25<
0<
1234
1234<
N11:33
0<
#N7:0
15