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6-3

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

C79000-G7076-C504-02

STEP 7 represents some ladder logic instructions as boxes with lines

indicating inputs and outputs (see Table 6-4). The inputs are on the left side

of the box; the outputs are on the right side of the box. You fill in the input

parameters. For the output parameters, you fill in locations where the STEP 7

software can place output information for you. You must use the specific

notation of the individual data types for the parameters.

The principle of the enable in (EN) and enable out (ENO) parameters is

explained below. For more information on input and output parameters, see

the description of each instruction in this manual.

Table 6-4 Ladder Logic Instruction as Box with Inputs and Outputs

Box Name Section in This Manual

DIV_R

IN1

IN2 OUT

ENO

Divide Real 12.5

Passing power to (activating) the enable input (EN) of a ladder logic box

causes the box to carry out a specific function. If the box is able to execute

its function without error, the enable output (ENO) passes power along the

circuit. The ladder logic box parameters EN and ENO are of data type BOOL

and can be in memory area I, Q, M, D, or L (see Tables 6-5 and 6-6).

EN and ENO function according to the following principles:

S If EN is not activated (that is, if it has a signal state of 0), the box does

not carry out its function and ENO is not activated (that is, it also has a

signal state of 0).

S If EN is activated (that is, if it has a signal state of 1) and the box to

which EN belongs executes its function without error, ENO is also

activated (that is, it also has a signal state of 1).

S If EN is activated (that is, if it has a signal state of 1) and an error occurs

while the box to which EN belongs is executing its function, ENO is not

activated (that is, its signal state is 0).

You cannot place a box or an inline coil in a ladder logic rung which does not

start at the left power rail. The Compare instructions are an exception.

Most of the addresses in LAD relate to memory areas. The following table

shows the types and their functions.

Instructions as

Boxes with

Parameters

Enable In and

Enable Out

Parameters

Restrictions for

Boxes and Inline

Coils

Memory Areas and

Their Functions

Configuration and Elements of Ladder Logic

1 2 ... 72 73 74 75 76 77 78 79 80 81 82 ... 317 318

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