Rockwell Automation 1772-LP3 PLC - 2/30 Programmable Controller Programming and Operations Manual - Manual (Page 36)

Data Table
Chapter 3
3Ć9
Each bit in the input image table may have a corresponding real hardware
terminal on the I/O rack associated with it, although this may not always
be the case, since a corresponding input module may not actually be placed
in an I/O rack slot. If it does, the terminal address is the same as the bit
address. The correspondence between the two is illustrated in Figure 3.4.
CAUTION: Bit and/or word storage is not possible in the
input image table. Input bits which do not have an actual input
module in the I/O rack corresponding to address are cleared to
zero during each I/O scan.