Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 79)

Advanced Instruction Set
Chapter 6
6Ć22
Another characteristic of the internally indexed file instruction is that it has a
done bit and an enable bit. The done bit is bit 15 and the enable bit is bit 17.
These two bits are automatically entered from the counter address. The enable
bit is set when the rung logic goes from a false to true transition; the done bit is
set when the file instruction is completed.
There are three modes of operation based on the rate per scan. They are:
Complete
Distributed
complete
Incremental
We will discuss each mode of operation.
Complete Mode
In the complete mode, the rate per scan is equal to the file length value and the
entire file is operated upon in one scan. For example, if there are 12 words in
your file and your rate per scan value is 12 then all 12 words will be operated
upon during one scan.
For each false-to-true transition of the rung condition, the instruction is enabled,
the accumulated value of the file counter is internally indexed from the first to
the last word of the file. As the accumulated value points to each word, the
operation defined by the file instruction is performed. After the instruction has
operated on the last word, the done bit (bit 15) is set. When the rung condition
goes false, both the done and enable bits are reset and the counter resets to
position 001. If the rung was enabled for only one scan, the done bit would
come on during the scan and remain set for one additional scan.
Distributed Complete Mode
In the distributed complete mode, the rate per scan is less than the file length
value and the entire file is operated over several program scans. For example, if
there are 12 words in your file and your rate per scan value is 3, then 3 words
will be operated upon during each scan. Therefore, it would take 4 scans to
execute the entire file instruction operation.
For each true rung condition, the instruction is enabled. The number of words
equal to the rate per scan is operated upon during one scan. The process is
repeated over a number of scans until the entire file has been operated upon.
Once the file instruction is enabled it remains enabled for the number of scans
necessary to complete the operation. The rung could become repeatedly false
and true during this time without interrupting the operation of the instruction.
At the time of completion, if the rung is true, the enable bit (bit 17) and the
done bit (bit 15) are both set. If the rung is false, the enable bit is reset after the
Modes of Operation