Rockwell Automation 1772-LP3 PLC - 2/30 Programmable Controller Programming and Operations Manual - Manual (Page 192)

Block Transfer
Chapter 10
10Ć9
WARNING: When programming multiple writes (or reads) to
the same module, it is possible that a desired transfer will not
take place or the number of words transferred will not be the
number intended. Invalid data could be sent to an analog
output device (or could be operated upon in subsequent scans)
resulting in unpredictable and/or hazardous machine operation.
Refer to the module user’s manual for any information unique to that
module.
The programming example shown in Figure 10.5 illustrates how multiple
reads of different block lengths from one module can be programmed.
When any one of the input switches is closed, the rung is enabled and
the block length is established. The last rung enables the block transfer
instruction regardless of the previous changes in status of the enable bit.
The examine off instructions prevent more than one of the the block
transfer instructions from being energized in the same scan.