Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 111)

Data Transfer File Instructions
Chapter 11
11-2
Figure 11.1
Types of Counter Indexing
DM
WordĆtoĆFile Move
Counter Addr:
Position:
FIle Length:
Word Addr:
File R:
001
007
110
500Ć 506
200
200
15
DM
FileĆtoĆWord Move
Counter Addr:
Position:
FIle Length:
Word Addr:
File A:
001
007
110
400Ć 406
200
200
15
EN
FileĆtoĆFile Move
Counter Addr:
Position:
FIle Length:
File R:
File A:
001
007
500Ć 506
400Ć 406
200
200
17
Rate Per Scan 007
DM
200
15
externally indexed
file instructions
internally indexed
file instructions
Externally Indexed
An externally indexed counter must be controlled by other rungs of your
program. The counter address is used to identify the file instruction. The
counter address holds the accumulated value. The accumulated value of
the counter points to the file’s position value. The position value is the
accumulated value and it represents the specific word location within the
file. The preset value of the counter represents the length of the file.
Another characteristic of the externally indexed file instruction is that it
only has a done bit. This is bit 15. The done bit is automatically entered
from the counter address. It is set when the operation is complete and
remains set as long as the rung condition is true.
Internally Indexed
Internally indexed means that the counter is internally incremented by the
instruction itself. No outside control is required. You assign an address to
the counter.
In Figure 11.1 notice that a value for rate per scan is needed. The rate per
scan defines the number of words which are operated upon during one
scan. For example, suppose you have a file that contains twelve words. If
you assign the value of 004 for the rate per scan that means that the
instruction executes four words per scan at a time. Therefore, the entire
operation is completed in three consecutive scans.