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8-2

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

C79000-G7076-C504-02

8.1 Overview

Bit logic instructions work with two digits, 1 and 0. These two digits form

the base of a number system called the binary system. The two digits 1 and 0

are called binary digits or bits. In the world of contacts and coils, a 1

indicates activated or energized, and a 0 indicates not activated or not

energized.

The bit logic instructions interpret signal states of 1 and 0 and combine them

according to Boolean logic. These combinations produce a result of 1 or 0

that is called the “result of logic operation” (RLO, see Section 6.3). The logic

operations that are triggered by the bit logic instructions perform a variety of

functions.

There are bit logic instructions to perform the following functions:

S Normally Open Contact and Normally Closed Contact each check the

signal state of a contact and produce a result that is either copied to the

result of logic operation (RLO) bit or is combined with the RLO. If these

contacts are connected in series, they combine the result of their signal

state check according to the And truth table (see Table 6-8); if they are

connected in parallel, they combine their result according to the Or truth

table (see Table 6-9).

S Output Coil and Midline Output assign the RLO or store it temporarily.

S The following instructions react to an RLO of 1:

– Set Coil and Reset Coil

– Set Reset and Reset Set Flipflops

S Other instructions react to a positive or negative edge transition to

perform the following functions:

– Increment or decrement the value of a counter

– Start a timer

– Produce an output of 1

S The remaining instructions affect the RLO directly in the following ways:

– Negate (invert) the RLO

– Save the RLO to the binary result bit of the status word

In this chapter, the counter and timer coils are shown in their international

and SIMATIC forms.

Explanation

Functions

Bit Logic Instructions

1 2 ... 95 96 97 98 99 100 101 102 103 104 105 ... 317 318

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