Rockwell Automation 1771-IS 5V DC INPUT MOD - Manual (Page 18)

Module Preparation, Wiring and
Installation
Chapter 2
2-11
CAUTION: This module is not compatible with TTL
switching. The external power source will damage the module.
When selecting BCD thumbwheel switches, be sure that they are equipped
with decoupling diodes or that terminals are available on the thumbwheel
switch so that the diodes can be wired directly to the switch assembly.
The diode polarity must be set for low = TRUE operation. Cathodes must
be connected to the switch contacts and anodes to the module inputs (lines
8, 4, 2, 1).
When selection thumbwheel switches, be sure to select a BCD type.
Decimal thumbwheel switches should be avoided because the 10 discrete
connections for each digit would not be compatible with the 4 BCD coded
input terminals for each digit on the module swingarm.
Diode Selection
Any diode can be used for diode decoupling that has a forward voltage
drop of approximately 0.7 volts at 14 mA forward current. A 1N914 is a
typical diode that can be used.
Cable Selection
The maximum cable capacitance can be .039 microfarad. The wire size
can be 20 gauge or larger for cables shorter than 100 feet; and 18 gauge
for up to 400 feet. The cable should be shielded and should not exceed
400 feet in length.
The backplane connector should be keyed to accept only this module after
its position in the I/O rack has been determined. The module can be
placed in any I/O slot except for the left-most slot. Th slot is reserved for
the processor module in a single rack system or the I/O adapter module in
a multi-rack system.
Plastic keying bands shipped with the I/O chassis should be used. The
position of the keying bands on the upper backplane connector must
correspond to the mating slots on the module connector.
Keying