5
and valves; affect the controlled system directly. Others; such as the indicator
lights, buzzers, and alarms; provide output to notify personnel.
Solenoid
Servomotor
Stepping motor
1-3 How Does a PC Work?
PCs operate by monitoring input signals and providing output signals. When
changes are detected in the signals, the PC reacts, through the user-pro-
grammed internal logic, to produce output signals. The PC continually scans the
program in its memory to achieve this control.
Block Diagram of PC
Power Supply
Input Output
CPU
Memory
Programming
Device
Signals
from
switches,
sensors,
etc.
Signals to
Solenoids,
motors,
etc.
A program for your applications must be designed, and stored in the PC. This
program is then executed as part of the cycle of internal operations of the PC.
How Does a PC Work? Section 1-3
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