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8-4

Ladder Logic (LAD) for S7-300 and S7-400

C79000-G7076-C504-02

8.3 Normally Closed Contact

You can use the Normally Closed Contact (Address) instruction to check the

signal state of a contact at a specified address. If the signal state at the

specified address is 0, the contact is closed and the instruction produces a

result of 1. If the signal state at the specified address is 1, the contact is open

and the instruction produces a result of 0.

When Normally Closed Contact (Address) is the first instruction in a logic

string, this instruction stores the result of its signal check in the result of logic

operation (RLO) bit.

Any Normally Closed Contact (Address) instruction that is not the first

instruction in a logic string combines the result of its signal state check with

the value that is stored in the RLO bit. The instruction makes the

combination in one of the two following ways:

S If the instruction is used in series, it combines the result of its signal state

check according to the And truth table.

S If the instruction is used in parallel, it combines the result of its signal

state check according to the Or truth table.

Table 8-2 Normally Closed Contact (Address) Element and Parameter

LAD Element Parameter Data Type Memory Area Description

BOOL

TIMER

COUNTER

I, Q, M, T, C,

D, L

The address indicates the bit whose

signal state is checked.

I 0.0

I 0.2

Status Word Bits

I 0.1

BR CC 1 CC 0 OV OS OR STA RLO FC

Write – – – – – x x x 1

Power flows if one of the following conditions exists:

S The signal state is 1 at inputs I 0.0 and I 0.1

S Or the signal state is 0 at input I 0.2

Figure 8-2 Normally Closed Contact (Address)

Description

Bit Logic Instructions

1 2 ... 97 98 99 100 101 102 103 104 105 106 107 ... 317 318

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