Programming FCs (Functions) and FBs for S7 Ethernet CPs

6.4FCs for Access Coordination with FETCH/WRITE

Overview

The following FCs are available for FETCH/WRITE function to coordinate access:

FC

can be used with:

Meaning

 

 

 

 

 

S7 – 300

S7 - 400

 

 

 

 

 

AG_LOCK (FC7)

x

x

Locks external data access

 

 

 

with FETCH/WRITE.

 

 

 

 

AG_UNLOCK (FC8)

x

x

Releases external data

 

 

 

access with FETCH/WRITE.

 

 

 

 

Caution when Configuring

If you use FCs AG_LOCK and AG_UNLOCK, you must specify the following information for S7-400 stations in the configuration:

Sin HW Config

In the “Addresses” tab, the option “Address setting for LOCK/UNLOCK” must be selected.

How the Block Works

With these FCs, you can coordinate access to system memory areas so that no inconsistent data are created and transferred. The control is from the user program in the S7 CPU that can, if necessary disable an external FETCH/WRITE access using an AG_LOCK call. After a certain time or after the local write/read access is completed, an AG_UNLOCK job can be used to enable external access again.

Another advantages is that this access lock only applies to the FETCH/WRITE connection specified in the call. If more than one FETCH/WRITE connections are configured, these can, for example, be used for certain specific system areas and a selective access coordination can be implemented.

The following diagram illustrates the usual chronological sequence of memory access coordination controlled in the user program with AG_LOCK and AG_UNLOCK.

SIMATIC NET NCM S7 for Industrial Ethernet

191

Release 6/2003

C79000–G8976–C129–07

Page 191
Image 191
Siemens NCM S7 appendix FCs for Access Coordination with FETCH/WRITE, Locks external data access, With FETCH/WRITE

NCM S7 specifications

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