Rockwell Automation 1771-IE,D17716.5.7 ANAL.INPUT MOD. - Manual (Page 38)

Appendix
B
BĆ1
Single Channel Transfer for PLC Processors
Programming techniques used in this example program (Figure B.1) for
the PLC processor include:
I/O scan counter
conditional ignore zone
I/O Scan Counter
The I/O scan counter (rungs 1-3) controls the transfer sequence and gives
the module sufficient time to respond to channel byte and update select
commands.
The scan counter increments only when a program scan and I/O scan have
occurred. It does this by manipulating a specially chosen bit. The bit
must be in the input image table, and must have an input module
associated with it. The terminal corresponding to this bit must NOT have
an input device wired to it so it can be turned OFF each I/O scan. Choose
a bit which satisfies these conditions:
It has an input address with the same assigned rack number as the input
module.
The input terminal associated with that bit address should be in a
module group with a higher module group number than the one the
input module is in.
The input terminal associated with that bit address must be unused.
Wire it to DC COMMON or L2 (AC Low) to guard against wiring it to
an input device.
Conditional Ignore Zone
The conditional ignore zone controls multiple output instructions based on
a set of overriding conditions. When these conditions are true, the outputs
within the zone are controlled by the conditions in their individual rungs.
When false, the zone outputs are held in their last state, whether ON or
OFF.
Example Program