Publication 1747-RM001G-EN-P - November 2008
Application Specific Instructions 7-19
After the instruction compares the last bit in two files, the done bit (bit 13 DN
on the compare control element) is set. Then, when the rung goes false, the
instruction resets the:
• enable bit.
• found bit (if set).
• compare done bit.
• result done bit (if set).
The control position counters are reset on the next false-to-true rung
transition. To enable this mode of operation, set the inhibit bit (IN=1) either
by ladder program or manually before program execution.
All Per Scan
After a false-to-true rung transition, the instruction searches for all mismatches
between the input and reference files in one program scan. Upon finding
mismatches, the instruction enters the position numbers of mismatched bits
into the result file in the order it finds them. After reaching the end of the
input and reference files, the instruction sets the FD bit if it finds at least one
mismatch. Then the instruction sets the DN bit.
If you use a result file that cannot hold all detected mismatches (if the result
file fills), the instruction stops and requires another false-to-true rung
transition to continue operation. The instruction wraps the new mismatched
bit positions into the beginning of the result file writing over the old.
After completing the comparison and when the rung goes false, the instruction
resets the:
• enable bit.
• found bit (if set).
• compare done bit.
• result done bit (if set).
The control position counters are reset on the next false-to-true rung
transition. To enable this mode of operation, reset the inhibit bit (IN=0) by
ladder program or manually before program execution.
TIP
To detect one mismatch at a time, set the result
length value to one.
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