Applies To:
  • CitectSCADA 5.xx

How do I configure a serial connection from Citect to the Siemens S7 PLCs using the S7 Drivers?

What software and hardware are required for this connection?


It is possible to communicate serially to the Siemens S7 PLCs using the S7 drivers via MPI and Profibus-DP protocols.  To use the serial connection, a "PC Adapter" cable is required from Siemens.  This cable has a built-in MPI/DP to RS232C converter (P/N 6ES7 972-0CA22-0XA0) and is capable of transmission speeds of 19200 or 38400 Baud rates.

Note: The older version of the Adapter Cable (P/N 6ES7 972-0CA20-0XA0) can only support 19200 Baud.

The protocols which can be used for serial connections are MPI and Profibus-DP.  Though only the MPI-serial connection has been tesed, the Profibus-DP to serial connection should work as well.  For this test, STEP7 V5 + Spk3 and the Simatic NET CD (November 1999) were used.

Software Requirements:

Siemens COML S7 program. This software is required as per "normal" operation of the S7 driver using for example, a CP5412A2 card.

Setup procedure for the S7-PLC:

There is no special setup required on the S7 PLC side except to define an MPI or Profibus-DP network at the appropriate baud rate.

Setup procedure for the PC:

The setup procedure is as per "normal" operation of the S7 driver using for example, a CP5412A2 card except for the following:

i. Run the Siemens "Setting PG/PC Interface" program in Control Panel.

ii. Select the required Access Point then select the "PC Adapter(MPI)" or "PC Adapter(Profibus)" as the Interface Parameter


iii. Click on Properties tab -> Local Connection to set the COM port and baud rate. (To use 38.4KBaud, make sure the switch on the PC Adapter cable is set at the right setting. It is default to 19.2K)

iv. Click SAPI S7 tab to enter the path for the database generated by the COML S7 program.