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

Table of Contents
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The module reads the status of switch contacts by enabling and reading a
“bank” of 8 contacts at a time. This requires that the contacts be grouped
and that diode decoupling be used to prevent the appearance of a
“phantom” contact closure. Up to 9 banks of 8 contacts per bank can be
handled by the module. Power to the switch banks is provided by the
module.
Contact scanning occurs until the module is interrupted by a read
instruction from the PC processor. Contact status is stored in on-board
RAM memory until the module outputs the contact status to the
processor. Therefore switch scanning by the module is totally
independent of I/O scanning by the processor. Module scanning is
user-selectable at a normal or fast rate with contact de-bouncing.
In many applications, it is necessary to set or change the preset values of
timers or counters or the values of process variables. It is convenient to
do this using BCD thumbwheel switches (Figure 1.2). Applications that
require the use of multiple thumbwheel switches include, but are not
limited, to the following:
control of chemical processes
production-part adjustments used in the automatic balancing of tires
control of pallets in materials handling
cycle time adjusments in production machines and processes
Figure 1.2
Typical 3-digit Thumbwheel Switch
+
–
6
–
9
+
–
2
+
17928
The DC (5V) Multiplexer Input Module saves I/O space and user
program. It can handle the switch input from up to six 3-digit or four
4-digit BCD thumbwheel switches. It can also handle up to 72 discrete
contact switches.
Typical Applications