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lines of the program at a time and can be used to observe the operation of the

circuit as it’s operating.

Secondary Storage Unit

• This unit related to CPU where all programand information were kept

VDU Unit

• Secondary storage data usually resides on devices with non-volatile memory

(NVM), such as hard disk drives (HDDs), solid-state drives (SSDs), tape

drives,optical media and cloud storage

Power Supply Unit

• Supply DC power to CPU, Input Unit and Output Unit.

• The most PLC works with power 24VDC or 220VAC

• The big PLC has the separate power supply and the smallPLC has power

supply which is one.

Printer Unit

• Used to print control system programming that controlled by PLC whether

graphicallyor text.

2.2 PLC Selection

Input and Output Capacity

❖ Capacity means the number of connection terminals available on the Input

unit and Output unit.

❖ Need to choose the value of Input and Output capacity in accordance with

thework to be done by the PLC.

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