SIEMENS Communication SIMATIC S7-300 CP 342-5 FO

Product No. / Product DescriptionSIMATIC S7-300 CP 342-5 FO Ordering data


  • PROFIBUS DP master or slave with optical interface for connecting the SIMATIC S7-300 to PROFIBUS at up to 12 Mbit/s (including 45.45 Kbit/s)
  • Direct connection to the optical PROFIBUS network over the integrated fiber-optic interface for plastic and PCF fiber-optic cables
  • Communication services:
    • PG/OP communication (OP multiplexing)
    • S7 communication (client, server)
    • Open communication (SEND/RECEIVE)
  • Easy configuration and programming over PROFIBUS
  • Cross-network programming device communication through S7 routing
  • Modules can be replaced without the need for a PG


The CP 342-5 FO is the communications processor of the SIMATIC S7-300 for the PROFIBUS DP optical bus system.

The CP 342-5 FO has a fiber optic interface that facilitates interference-immune connections even in environments with severe levels of radio interference.

It relieves the CPU of communications tasks.

Communication of the SIMATIC S7-300 with:

  • the distributed I/O system ET 200 with integral optical interface
  • SIMATIC S7-400 with IM 467 FO and CP 342-5 FO
  • PC with CP 5613 FO
  • Remaining PROFIBUS nodes via the optical bus terminal (OBT)

The number of CPs that can be used is dependent on the performance range of the CPU and on the communications services used.


  • The fiber-optic technology is used when
    • the environment is subject to strong EMC interference,
    • strong potential differences exist and
    • high transmission rates are required.
  • The CP 342-5 FO is connected directly to the optical PROFIBUS and is therefore specially suited to harsh industrial environments
  • Expansion of the process I/O at SIMATIC S7-300 by several PROFIBUS DP interfaces
  • Optimization of applications and many application options through sending of data with S7 communication
  • Comprehensive control and monitoring through multiplex function with OP communication
  • Suitable for closed loop control tasks due to SYNC and FREEZE.


The CP 342-5 FO offers all the advantages of SIMATIC S7-300 system design:

  • Compact design;
    single standard width of the SM modules of the SIMATIC S7-300
  • Integrated fiber-optic cable interface;
    2 female duplex connectors for direct connection to the optical PROFIBUS over 2 x 2 male simplex connectors and 2 plug-in adapters
  • 4-pin terminal block for connecting the external supply voltage of 24 V DC
  • Easy installation;
    the CP 342-5 FO is snap-mounted on the S7-300 DIN rail and connected to adjacent modules through the bus connectors. There are no slot rules.
  • In combination with IM 360/361, the CP 342-5 FO can also be used in an expansion rack (ER).
  • User-friendly wiring;
    female FOC connector and the terminal block are easily accessible.
  • The CP 342-5 FO can be operated without a fan; a back-up battery or a memory module are not required.

CP 342-5 FO

The CP 342-5 FO provides access to different communication services of the PROFIBUS bus system:

  • PROFIBUS DP (according to IEC 61 158/61784, master or slave)
  • PG/OP communication
  • S7 communication
  • Open communication (SEND/RECEIVE)


The CP 342-5 FO operates as a DP-V0 Master according to IEC 61 158/EN 50 170 Volume 2 and processes the data transfer completely independently. It supports the services of the Master Classes 1 and 2.

The data areas of the distributed I/Os are transferred consistently between CP and CPU. This applies to the use of the CP as DP Master and as DP Slave. As DP Master, it permits connections to:

  • The distributed IO system ET 200 with integral optical interface (incorporate as DP-V0 Slave)
  • SIMATIC S7-300 with CP 342-5 FO as slave
  • The remaining DP-V0 slaves via the optical bus terminal (OBT).

The CP 342-5 FO also offers the SYNC, FREEZE and shared input/output functions, as well as the activation/deactivation of slaves.


The CP 342-5 FO as a DP-V0 Slave allows the SIMATIC S7-300 to exchange data with the SIMATIC S7-400 and with other PROFIBUS DP masters via the OBT. which allows a hybrid setup between SIMATIC S5/S7, PCs, ET 200 and other field devices to PROFIBUS DP. Function calls are required for DP communication, both as master and as slave. These (DP-SEND/DP-RECV) are shipped with STEP 7 and must be integrated in the user program.

PG/OP communication

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

  • S7 routing:
    With the aid of S7 routing it is possible to use programming device communication across networks.
    Via the CP 342-5 FO as many as 16 TD/OPs can be merged into one S7-300 station. This requires only one connection resource in the S7-CPU (multiplex channel). The multiplex channel supports the acyclic HMI services.

S7 communication

S7 communication is used for the coupling

  • between SIMATIC S7 automation systems
  • to HMI devices (OPs).
  • to PCs, e.g. CP 5711 with SOFTNET-PB S7, CP 5623 etc.

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 342-5 FO.

The client functionality is provided by means of loadable communication blocks.

Open communication (SEND/RECEIVE)

Based on Layer 2 (FDL) of PROFIBUS (IEC 61158/EN 50170), the CP 342-5 FO 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
    CP 5512, CP 5611 A2, CP 5621, CP 5613 A3, CP 5613 FO, CP 5614 A3, CP 5623, CP 5624
  • Systems of other makes 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.


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, or STEP 7 Professional V12 (TIA Portal) or higher, is required for configuring the full functional scope of the CP 342-5 FO. 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 PROFIBUS DP are included in the standard library of STEP 7. The function blocks for using the open communication (SEND/RECEIVE) and the S7 communication (S7 client) can be found in the SIMATIC NET library following installation of STEP 7.

System configuration of optical PROFIBUS DP with CP 342-5 FO