SIEMENS Communication SIMATIC S7-300 CP 343-5 Product Information

CP 343-5

Connection of SIMATIC S7-300 to PROFIBUS at up to 12 Mbit/s (including 45.45 Kbit/s)

  • Communication services:
    • PG/OP communication
    • S7 communication
    • Open communication (SEND/RECEIVE)
  • Easy configuration and programming over PROFIBUS
  • Can be easily integrated into the S7-300 system
  • Cross-network programming device communication through S7 routing
  • Modules can be replaced without the need for a PG
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  • Simple integration of the SIMATIC S7 into a multi-vendor automation group by means of PROFIBUS FMS
  • Extensive reduction of workload for the user of PROFIBUS FMS specification due to simple configuration and independent data conversion of data on the CP
  • Sub-process-oriented design of an automation solution through the use of several CPs
  • Integration of the SIMATIC S7-300 into existing systems by means of open communication
  • Universal application of the CP due to the parallel use of different communication services on one CP

ApplicationCP 343-5

The CP 343-5 communications processor is the module required for SIMATIC S7-300 and SIMATIC C7 for the PROFIBUS bus system.

It offloads communication tasks from the CPU.

S7-300 communication options using communication modules:

  • FMS communication with PROFIBUS FMS stations through PROFIBUS
  • Communication with programming devices, human machine interface devices
  • Communication with other SIMATIC S7 systems
  • Communication with SIMATIC S5 PLCs
  • The number of CPs that can be operated depends on the performance range of the CPU and the communication services used.


The CP 343-5 offers all the advantages of the SIMATIC S7-300 design:

  • Compact construction;
    single standard width of the SIMATIC S7-300 SM modules
  • If the adjacent module cannot be aligned without a gap when replacing earlier versions of modules, a dummy module must be used
  • 9-pin Sub-D socket for the bus interface to PROFIBUS
  • 4-pin terminal strip for connection of the 24 V DC external supply voltage
  • Easy installation;
    the CP 343-5 is mounted on the rail of the S7-300 and connected to the adjacent modules by means of the bus connectors. For the CP 343-5 the slots 4 through 11 in module racks 0 through 3 (linked via IM 360/361) are permissible
  • The CP 343-5 can also be operated in the expansion rack (ER) in conjunction with the IM 360/361
  • User-friendly wiring.
    Sub-D socket and terminal strip are easily accessible
  • The CP 343-5 can be operated without a fan. A back-up battery or memory module are not required.

The CP 343-5 provides the user with various communication services of the PROFIBUS bus system:

  • PG/OP communication
  • S7 communication (PG, OP, S7 controllers)
  • Open communication (SEND/RECEIVE)
  • PROFIBUS FMS (to IEC 61158/61784)

PG/OP communication

PG/OP communication allows all S7 stations connected to the network to be remotely programmed.

  • S7 routing
    With the aid of routing it is possible to use programming device communication across networks.

S7 communication

S7 communication is used for the coupling

  • between SIMATIC S7 automation systems (CP 343-5 server only)
  • to HMI devices (OPs).
  • to SIMATIC 505
  • to PCs, e.g. with CP 5512, CP 5611 A2, CP 5621 and SOFTNET-PB S7 or CP 5613 A2, CP 5613 FO, CP 5614 A2, CP 5623, CP 5624 and HARDNET-PB S7.

Communication with PG and OP takes place without further configuration. In addition, the central controller can also be programmed and configured on a distributed basis via the CP 343-5.

Open communication (SEND/RECEIVE)

Based on Layer 2 (FDL) of PROFIBUS (IEC 61158/61784), the CP 343-5 offers a simple, optimized interface for process or field communication.

This interface offers integrated, high-performance communication between SIMATIC S5, SIMATIC S7, SIMATIC 505 and PC. SEND/RECEIVE provides not only the SDA service (PLC/PLC connections) but also the SDN service (broadcast, multicast).

The communication partners are the automation systems:

    with CP 342-5, CP 343-5, CP 443-5 Extended and Basic
    with S5-95U with PROFIBUS interface, S5-115U/H, S5-135U, S5-155U/H with CP 5431 FMS/DP,
  • SIMATIC 505 with CP 5434-FMS
  • PCs with CP 5512, CP 5611 A2, CP 5621, CP 5613 A2, CP 5613 FO, CP 5614 A2, CP 5623, CP 5624
  • Non-Siemens systems that are equipped with an FDL interface.

To use SEND/RECEIVE, function calls are required (PLC-SEND/PLC-RECEIVE), which must be linked into the STEP 7 user program.


PROFIBUS FMS, according to PROFIBUS IEC 61158/61784, permits the transmission of messages via various FMS services:

    for read or write access to variables of the communication partner from the user program (by means of a variable index or variable name),
    for the transfer of its own variable values to the communication partner. Partial access to variable values is supported. The communication is processed over acyclic connections (master/master, master/slave), over acyclic connections with a slave initiative and cyclic connections.
    (Report) permits unconfirmed transmission of variables by an FMS server. This job type is used particularly for transmission on broadcast FMS connections.
    for requesting the identification features of the communication partner
    for requesting the partner status


Extensive diagnostic options are available via STEP 7, including:

  • Status of the CP
  • General diagnostics and statistics functions
  • Connection diagnostics
  • Bus statistics
  • Message buffer


STEP 7 V5.1 SP2 or higher is required for configuring the full functional scope of the CP 343-5. In Version V5 or higher of STEP 7, the configuration data of the CP can also optionally be stored on the CPU and is retained even if there is a power failure. A module can therefore be replaced without having to reload the configuration data from a programming device. The CPU transfers the configuration data to the CP during start-up. Attention should therefore be paid to the memory capacity of the S7-CPU.

Configuration and programming of all SIMATIC S7 controllers connected to the network is possible over the network.

The function blocks for using the open communication (SEND/RECEIVE) and FMS can be found in the SIMATIC NET library following installation of STEP 7.