Rockwell Automation 2711 PANELBUILDER SOFTWARE USER MANUAL - Manual (Page 361)

The Objects
Chapter 10
10-96
IMPORTANT: All PLC input addresses can be preset except Time and
Date Transfer, Screen Number Transfer, Alarm Window Address, Set Bit
Cursor Point, Normally Open Push Button, Normally Closed Push Button,
and Latched Push Button. Since addresses can overlap, it is possible to
preset even these addresses, by sharing them with a presettable address.
Safety Considerations for Retentive Objects
Instead of using a Retentive Object to start a machine or process, use a
Momentary Input Object such as a Momentary Push Button. Also, make
sure that the PLC controller is programmed to stop any machines or
processes whenever the remote I/O communication is interrupted, so that a
machine or process can only be restarted by an operator.
ATTENTION: Never use a Retentive Object to initiate a
process or turn on a machine. Here’s why: Let’s say your PLC
controller was programmed to turn a machine on whenever a
Maintained Push Button was set to one. If remote I/O
communication were temporarily cut while the Maintained Push
Button was set to one, the machine would automatically restart
as soon as communication resumed. Similarly, since the
Retentive Object’s value is retained even after power is
removed, the machine could start up automatically when you
re-applied power to the terminal, if the Maintained Push Button
had been set to 1 when the terminal was powered down. In other
words, the machine could start up automatically, without the
operator being aware of it.