Siemens CP 243-1 Operating Instructions Manual page 18

Application and properties
1.5 S7 communication via Industrial Ethernet
Note
Autonegotiation mode only works when all connected network components support this
mode.
Industrial Ethernet and TCP/IP do not allow time-deterministic data flows. There is no way to
know when a remote CPU will execute the requests. The responses of the remote CPU are
asynchronous to the CPU cycle of the local S7-200 CPU. This is why TCP/IP-based
communication is not ideally suitable for use in distributed applications with strict time
requirements (for example control circuits, cyclic precisely timed sampling).
S7 communication
The XPUT and XGET S7 services are used to exchange data between two controllers. The
CP 243-1 can be used both as client and as server.
Communication between a CP 243-1 and an OPC server running on a PC/PG is based on
the READ and WRITE S7 services. In this case, the CP 243-1 always functions as the
server. Other S7 services, for example the service for automatic querying of objects currently
on an S7-200 (DBs, ...) are not supported here.
The following data types or data areas are supported by the CP 243-1:
● CP 243-1 as client
● CP 243-1 as server
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Read and write access:
– Data type is always BYTE
– Only variables can be accessed on the local system.
– Accessible memory areas on the partner system are inputs, outputs, bit memory and
variables when an S7-200 is the partner.
– Accessible memory areas on the partner system are inputs, outputs, bit memory and
data areas when an S7-300 or an S7-400 is the partner.
Write access:
– Data type is BOOL, BYTE, WORD or DWORD
– The use of the data types CHAR, INT, DINT and REAL depends on the firmware
version of the S7-200 CPU being used.
– Accessible memory areas on the local system are inputs, outputs, variables, bit
memory and status bits.
Read access:
Operating Instructions, 03/2012, C79000-G8976-C244-02
CP 243-1