Siemens NAN 67 Series Manual de Serviço descarregar pdf (Página 238)

20-4

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

C79000-G7076-C504-02

20.2 Calling FBs, FCs, SFBs, SFCs, and Multiple Instances

You can call function blocks (FBs), functions (FCs), system function blocks

(SFBs), and system functions (SFCs), and multiple instances by selecting

them from the “Program Elements” list box. They are at the end of the list of

instruction families under the following names:

S FB Blocks

S FC Blocks

S SFB Blocks

S SFC Blocks

S Multiple Instances

S Libraries

When you select one of these blocks, a box appears on your screen with the

number or symbolic name of the function or function block and the

parameters that belong to it.

The block that you call must have been compiled and must already exist in

your program file, in the library, or on the CPU.

If the call FB, FC, SFB, SFC, and multiple instances instruction is executed,

it performs the following functions:

S Saves the address that it needs to return to the calling block

S Saves the selectors of both current data blocks (DB and DI)

S Changes the previous local data range to the current local data range

S Pushes the MA bit (MCR Active bit) to the block stack (BSTACK)

S Creates the new local data range for the called FC or SFC

Note

When the DB and DI registers are saved, they may not point to the data

blocks that you opened. Because of the copy-in and copy-out mechanism for

passing parameters, especially where function blocks are concerned, the

compiler sometimes overwrites the DB register. See the Programming

Manual /234/ for more details.

After this, program processing continues in the called block.

Description

Program Control Instructions

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