Siemens S7-200 User Manual download pdf (Page 9)

Here are the Bits

The smallest unit to be processed is the bit!

The bit can assume two states:

1) "1" meaning "bit set" or state is "true",

2) "0" meaning "bit not set " or state is "untrue",

In a method familiar to you, the two binary states "1" and "0" can be represented as

electrical circuits, that is, they can be represented by switches.

A closed switch:

Current flows so bit state = "1"

and an open switch:

No current flows so bit state = "0".

From here it requires only a short step to the

representation of logic operations as circuits,

e.g. series connection of two contacts.

The AND operation of inputs I0.0 and I0.1

is represented as shown on the right.

This is represented as follows in LAD:

Finally, a small convention.

The following applies for positive logic:

24V = high-level = "1" und

0V = low-level = "0".

The following applies for negative logic:

0V = low-levgel = "1"

24V = high-level = "0".

"1" ="true" =

Current flows

"0" = "untrue" =

No current

flows

AND operation

positive logic

negative logic

Revision

What you know already...

- A Few Words of Revision

- Here are the Bits

- Current Flow in the Ladder Diagram

- The PLC Cycle

Latching Revision

Pulse-Oper-

ated Switch

Off-Delay

Timer

Sequencer Appendix

1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 73 74

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Siemens S7-200 User Manual Page 9

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