Siemens S7-400 Service Manual download pdf (Page 123)

Program Control Instructions

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

A5E00706949-01

10-9

Example

MCRA

Q 4.0

OPN

DB10

SFB 8

EN ENO

REQ DONE

ID ERROR

R_ID STATUS

SD_1

SD_2

SD_3

SD_4

M11.0

READY

M10.0

DB 8

CODE

DW12

DW14

DW16

OPN

DB10

The Ladder rungs shown above are program sections from a function block written

by a user. In this FB, DB10 is opened and MCR functionality is activated. If the

unconditional call of SFB8 is executed, the following occurs:

The return address of the calling FB plus selection data for DB10 and for the

instance data block for the calling FB are saved. The MA bit, set to "1" in the

MCRA instruction, is pushed to the B stack and then set to "0" for the called block

(SFB8). Program processing continues in SFB8. When SFB8 is finished, program

processing returns to the calling FB. The MA bit is restored and the instance data

block of the user-written FB becomes the current instance DB. If the SFB8 is

processed correctly, ENO = "1" and therefore Q4.0 = "1".

Note

When opening an FB or SFB, the number of the previously opened DB is lost. The

required DB has to be reopened.

1 2 ... 118 119 120 121 122 123 124 125 126 127 128 ... 227 228

No comments

Siemens S7-400 Service Manual Page 123