Rockwell Automation 1771-IS 5V DC INPUT MOD - Manual (Page 17)

Module Preparation, Wiring, and
Installation
Chapter 2
2-10
Diode Decoupling
Decoupling diodes prevent unwanted currents from circulating through
the switch circuits and causing the false appearance of switch closures.
Use decoupling diodes when the application calls for more than 8 switch
contacts. Some thumbwheel switches have provision at the switch
terminals for wiring the diodes. Otherwise, a separate terminal strip
should be used for wiring a diode to each switch terminal. Be sure that all
diodes are wired with the same polarity as shown in Figure 2.4, Figure 2.5
or Figure 2.6.
The following information will be helpful when selecting the cable and
components, and when wiring the switches and decoupling diodes to the
module.
Low - TRUE Logic
Module operation is based on a low = TRUE logic. Enable lines, A
through I, ground the inputs connected to them through the switch
contacts. This low = TRUE condition is interpreted as a logic “1” (or
contact closed) by the module.
No External Power
The switches connected to the module are powered by the module enable
lines. Any additional power source must NOT be used.
CAUTION: Damage to the module will result if any external
power source is connected to the module field wiring arm
terminals.
Switch Selection
Any contact closure switch than can successfully handle 8 to 14mA of
current at 5V DC can be used. The minimum OFF resistance can be 10 K
ohms. The maximum ON resistance can be 10 ohms including the cable
resistance.
Additional Considerations