Rockwell Automation 1771-IS 5V DC INPUT MOD - Manual (Page 25)

Programming and Operation
Chapter 3
3-6
Important: The 16-bit data position (switch #2 ON) should be selected
when 4-digit thumbwheel switches or discrete contact switches are used.
Otherwise switch status data from these devices can become scrambled
when transferred to the data table.
Discrete Contact Switch Data (16-Bit storage)
Data is loaded into memory on the basis of whether you have selected the
maintained or momentary switch contact mode (switch #4).
Momentary Contact Mode
When up to 72 discrete contact switches are wired as switch banks,
Figure 3.4a, the settings are stored automatically in the data table after a
block transfer as shown in Figure 3.4b. The first word is reserved for
diagnostic data. Each remaining word stores the status of two switch
banks. The settings of a switch bank are represented by S7, S6, S5, S4,
S3, S2, S1, S0.
Data of odd-numbered switch banks appears in the lower byte, and data of
even-numbered switch banks appears in the upper byte, of their respective
data table words. For example, observe how the ON/OFF settings of
switch banks 5 and 6 are loaded into the data table in Figure 3.4b.