Applies To:
  • CitectSCADA 5.xx

The Siemens S7 Series of PLCs support a number of different protocols. What are these protocols, and does Citect support them? If so, how? 


S7 protocol
The S7 protocol is offered on numerous different physical media including the MPI network, Profibus Network, and Industrial Ethernet network. In all cases, the S7 protocol is supported with the use of the SSEVEN driver, however the exact hardware and software requirements for Citect to establish communications will differ.

S7 protocol on MPI: The MPI (multiport interface) protocol is primarily used by programming packages. It has a data transfer rate of 187.5 kbps, and can support up to 32 stations. The Siemens CP5412A2 card and Siemens S7-5412/WinNT software is presently recommended by Ci Technologies in this instance. Although MPI is based on an RS485 network, normal RS485 cards cannot be used with MPI.

S7 protocol on Profibus: It has a data transfer rate of up to 1.5 Mbps. The Siemens CP5412A2 card and Siemens S7-5412/WinNT software is presently recommended by Ci Technologies in this instance.

S7 protocol on Industrial Ethernet: Has a communication rate of standard Ethernet (based on electrical or optical LANs). The Siemens CP1413 card and the Siemens S7-1413 software is presently recommended by Ci Technologies.

Profibus FMS (also referred to as Sinec L2-FMS)
Profibus FMS is typically used where data transfer of large blocks of information are required, for example SCADA / PLC communications. Citect supports this protocol with the use of the PROFI, PROFIB, and PROFIBD drivers. An additional driver using the SST 5136 card is under development.

Profibus DP (also referred to as Sinec L2-DP)
Profibus DP is typically used by PLCs as a field level bus, communicating to field I/O. Citect supports this protocol with the use of the APPLIC Citect driver, although additional drivers for Softing and SST products are planned.

The PPI (point-to-point interface) protocol is used for communications to the S7-200 Series. Citect supports this protocol with the use of the APPLIC and PPI Citect drivers. The APPLIC driver requires additional hardware from Applicom International. The PPI driver is currently developed by a third party and support for this driver may be limited. The S7-200 also supports a mode that allows MODBUS communications using and function block and Citect's MODBUS driver. The function block is available from Ci Technologies, but sample code for Modbus communications is listed in Siemens manuals.

An enhanced version of the PPI protocol. Supported by the APPLIC Citect driver.

The 3964R is a transport layer protocol only, and must be used in conjunction with a application layer protocol. The S7 series communications processors CP340, CP441-1, and CP441-2 support the 3964R protocol. PLC support of the application layer protocols using these CPs is usually performed using function blocks. An exception to this case is the CP441-2, which supports the RK512 protocol with no function block required.

The most well known application layer protocol in relation to the 3964R transport protocol is the RK512 protocol. Citect supports the RK512/3964R combination using the SIEMENS driver. In the case where the RK512 protocol is not supported by the CP, a RK512 protocol can be purchased from:

Supplier - RK512 Driver for Step 7, FB10:
MESTRON Mess- und Regeltechnik GmbH
D-74321 Bleitigheim-Bissingen
Pleidelsheimer Strasse 9
Tel.  +49 7142 9551 0 
Fax. +49 7142 9551 49
Contact: R. Kästner.

Alternatively, a proprietary application layer protocol for use with the 3964R protocol has been developed by Ci Technologies. The S7PTP Citect driver has been developed for use with this protocol. The function blocks required can be obtained from Ci Technologies free of charge.