Rockwell Automation 1771-IE,D17716.5.7 ANAL.INPUT MOD. - Manual (Page 25)

Programming the Analog Input Module
Chapter 4
4Ć6
PLCĆ3 Family
If your application requires many block transfer modules, distribute the
modules over as many I/O chassis as possible to optimize transfer time
for the system as a whole.
Where allowed by your application, program block transfers to occur
less often than once per program scan.
Buffer incoming (BTR) data. Be sure it is valid before using it.
Examine the BTR done bit and any other status bit that monitors its
validity.
PLCĆ5/15
Incoming (BTR) data is buffered automatically by the processor.