Siemens SIMATIC NET S7-300 Manual page 156

5 Configuring Communication Connections
"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:
S S7 addressing mode: byte address
S S5 addressing mode: word address
This makes it possible for applications to access S5 or S7 stations without needing
to adapt the addresses. This is particularly interesting for existing S5 applications
than can be used unchanged to access S7 stations.
As default, the addressing mode for access to SIMATIC S7 is set (option selected).
System Memory
You can access the following address areas in the system memory on the
SIMATIC S7 PLC using FETCH or WRITE:
S Data blocks (DB)
(When accessing DBs, remember that the highest DB number is 255.)
S Bit memory (M, MB, MW, MD)
S Process image input table (I, IB, IW, ID)
S Process image output table (Q, QB, QW, QD)
S I/O area inputs (PIW, PID, PIB)
S I/O area outputs (PQW, PQD, PQB)
S Counters (C)
S Timers (T)
Links to Other Systems
The FETCH and WRITE modes supported on ISO transport connections and
ISO-on-TCP or TCP connections can be used with any other device to access the
S7 system memory areas.
To be able to use this type of access, for example for PC applications, you need to
know the PDU structure of the jobs. The required S7 or S5 headers for request
and response frames are 16 bytes long and their structure is described in the
Appendix.
A -156
S7-CPs for Industrial Ethernet Configuring and Commissioning
Release 01/2007
C79000-G8976-C182-07