Siemens S7-300 Configuration Manual page 112

Configuring communications connections
5.8 FETCH/WRITE mode
● SIMATIC S7 station:
– SEND / RECV
– SSEND / SRECV
– FETCH PASSIVE / WRITE PASSIVE
If you select the FETCH PASSIVE or WRITE PASSIVE mode for the ISO transport
connection, you can access the system areas on a SIMATIC S7 PLC from a SIMATIC S5
station or other third-party station (unspecified connection).
The connection can be used only for this mode. Sending or receiving using the FCs
AG_SEND/AG_LSEND/AG_SSEND or AG_RECV/AG_LRECV/AG_SRECV is then no
longer possible.
The connection is established passively; in other words, only the partner station
(SIMATIC S5 station, a PC station, or a non-SIMATIC station) can establish the
connection. The setting is made automatically in the "General" tab and cannot be
changed.
Note
With the S7-300 series, remember that this configuration uses one connection resource
(free connection for S7 functions) on the S7-300 CPU. CPU connection resources are
also used, for example, by S7-300 CPs, in the FMS mode or by PGs and OPs. For more
detailed information about the maximum number of connection resources, refer to /1/
(Page 227).
● SIMATIC PC station: FETCH ACTIVE / WRITE ACTIVE
If you select the FETCH ACTIVE or WRITE ACTIVE mode for the ISO transport
connection, you can access the system areas on a SIMATIC S7 PLC or a SIMATIC S5
station from the PC station.
The connection establishment is active; in other words, the partner station must wait for
connection establishment (passive connection establishment on the partner).
"S7 Addressing Mode" option
When you configure the FETCH ACTIVE / WRITE ACTIVE modes, you can select the
addressing mode. This specifies how the addresses will be interpreted in the FETCH/WRITE
call in the SIMATIC S7 station when accessing DBs:
● S7 addressing mode: byte address
● S5 addressing mode: word address
This makes it possible for applications to access S5 or S7 stations without adapting the
addresses. This is, for example, interesting for existing S5 applications that can now be used
unchanged to access S7 stations.
As default, the addressing mode for access to SIMATIC S7 is set (option selected).
112
Configuring and commissioning S7 CPs for Industrial Ethernet
Configuration Manual, 09/2013, C79000-G8976-C182-13