Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 23)

An Introduction to
Programmable Controllers
Chapter 2
2Ć9
Important: Figure 2.1 is for demonstration purposes only. We do not show the
associated wiring, a motor starter, or an emergency stop button.
Since the limit switch is wired normally-closed, the conveyor motor will run
until the arriving part opens the switch. At that time, the condition for
energizing the motor is not longer met. Therefore, the motor is de-energized.
When the condition is met, we say it is true. When the condition is not met, we
say it is false. There may be more than one condition which must be met before
an action is executed. When all the conditions are met, the action is executed
and we say the statement is true. When one or more of the conditions are false,
the action is not executed and we say the statement is false.
On power up, the processor begins the scan sequence (Figure 2.2) with the
I/O scan. During the I/O scan, data from input modules is transferred to the
input image table. Data from output image table is transferred to the
output modules.
Scan Sequence