Allen-Bradley PLC-5 User Manual page 63

When you specify indirect addresses, follow these guidelines:
You can indirectly address the file number, word number, or bit number.
The substitute address must be one of the following types: N, T, C, R,
B, I, O, or S. Any T, C, or R address must be a word-length sub-member
address, such as T4:0.ACC.
Enter the pointer address in brackets [ ].
Example Variable
N[N7:0]:0 File number
N7:[C5:7.ACC] Structure number
B3/[I:017] Bit number
N[N7:0]:[N9:1] File and word number The file number is stored in integer address
If you indirectly address the input or output image table,
ATTENTION
the value you specify in the integer file that you use for the
indirection (the pointer) is converted to octal when
executed by the instruction.
For example, if you enter O:[N7:0] and N7:0 contains the value 10, the value at
N7:0 is converted to octal and the resulting address is O:012, not O:010.
To monitor for invalid indirect addresses, condition the rung with the indirect
address with a limit test of the indirect address to ensure that the address stays
within the intended range. This is especially advisable if the PLC-5 controller
has no control over the indirect address, such as the value is determined by
values from an I/O module or a peer controller.
Addressing I/O and Controller Memory
Explanation
The file number is stored in integer address
N7:0.
The word number is the accumulated value
of counter 7 in file 5.
The bit number is stored in input word 17.
N7:0 and the word number in integer
address N9:1.
Publication 1785-UM012D-EN-P - July 2005
4-19