Siemens S7 1.6 FETCH/WRITE Services (Server)

Communication via Ethernet CPs in S7 Stations
30 SIMATIC NET NCM S7 for Industrial Ethernet
C79000-G8976-C129–06
1.6 FETCH/WRITE Services (Server)
Application
In addition to the SEND/RECEIVE interface, the FETCH/WRITE functionality
provides further services for S5-compatible communication on configured transport
connections.
The FETCH/WRITE interface is used primarily to attach SIMATIC S7 to SIMATIC
S5 and to other non-S7 stations (for example PCs).
SFETCH
The partner on the connection (SIMATIC S5 or non-S7 station) can read
system data on the SIMATIC S7 PLC.
SWRITE
The partner on the connection (SIMATIC S5 or non-S7 station) can write
system data on the SIMATIC S7 PLC.
From the point of view of the SIMATIC S7 PLC, this is a passive communication
function; the communications partner initiates the connection establishment.
For further information, refer to the system documentation of the SIMATIC S5 PLC
or the non-S7 station you are using.
Connection Types
To access a station with FETCH or WRITE functions, a FETCH passive or WRITE
passive connection must be configured. The following types are possible:
SISO Transport
SISO-on-TCP
STCP
Coordinating Access Using the User Program
To coordinate access, you can use the FCs AG_LOCK and AG_UNLOCK.
With these FCs, you can coordinate access to system memory areas so that no
inconsistent data are created and transferred.
SIMATIC S5
On the SIMATIC S5 station, the FETCH/WRITE services are configured and
started by READ ACTIVE/PASSIVE and WRITE ACTIVE/PASSIVE.