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20-6

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

C79000-G7076-C504-02

The parameters that have been defined in the VAR section of the block will

be displayed in the ladder box. Supplying parameters differs depending on

the type of block as follows:

S For a function (FC), you must supply actual parameters for all of the

formal parameters.

S The entry of actual parameters is optional with function blocks (FBs).

You must, however, attach an instance data block (instance DB) to the

FB. If an actual parameter has not been attached to a formal parameter,

the FB works with the values that exist in its instance DB.

S With multiple instances, you do not need to specify the instance DB since

the box that is called has already been assigned the DB number (for more

information about declaring multiple instances, refer to Section 3.5).

For structured IN/OUT parameters and parameters of the types “Pointer” and

“Array”, you must make an actual parameter available (at least during the

first call).

Every actual parameter that you make available when calling a function

block must have the same data type as its formal parameter.

For information on how to program a function or how to work with its

parameters, see the Programming Manual /234/.

Table 20-2 shows a box for calling FBs, FCs, SFBs, SFCs, and multiple

instances and describes the parameters common to the box for all these

blocks. When you call your block from the Instruction Browser, the block

number appears automatically at the top of the block (number of the FB, FC,

SFB, or SFC, for example, FC10).

Table 20-2 Box and Parameters for Calling FBs, FCs, SFBs, SFCs, and Multiple Instances

LAD Box Parameter Data Type Memory Area Description

Block no.

EN ENO

DB No.

DB No. BLOCK_DB –

Instance data block number. You need to

supply this information for calling FBs

only.

EN ENO

OUT

IN/OUT

EN BOOL I, Q, M, D, L Enable input

IN/OUT

ENO BOOL I, Q, M, D, L Enable output

DB13

Start

Stop

Length

Run

ENO

Calls FB10 (using

instance DB13)

I 1.0

I 1.1

MW20

M2.1

FB10

Actual addresses,

the values of which

are copied into

instance data block

DB13 before

processing FB10.

Formal parameters of the FB

The value of this parameter is

copied from DB13 into M 2.1 after

processing FB10.

Figure 20-3 Call FB from Box

Parameters

Program Control Instructions

1 2 ... 235 236 237 238 239 240 241 242 243 244 245 ... 317 318

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