Cartele S7


The new dummymodule from the Systeme Helmholz GmbH is for reserving slots for unparameterized signal modules.
The structure and address assignment is retained when it is eventually replaced by a signal module.
For 20-way or 40-way front connectors.

Meaning of the 8/9-Bit display of the placeholder module
There are two different methods of transmitting data on the backplane bus of the S7-3001):

- without parity Bit

Only the data bytes (8 Bits) are transmitted. This method is obsolete because errors during transmission cannot be detected and the I/Os may be incorrectly switched.

- with parity Bit

The new safe method transmits a parity bit in addition to the useful data (9 Bits per byte). That way transmission errors can be detected and incorrect connections avoided.

The CPUs known to us are capable of both transmission methods. Due to reasons of downward compatibility all I/O modules that are capable of the 9-Bit method can also be switched back to the 8-Bit method. This occurs when at least one module is plugged into the system that is only capable of the 9-Bit method.

The 8/9-Bit LEDs indicate which method the complete system is using.
If an 8-Bit module is used, all 9-Bit modules on the backplane will only use 8-Bit transmission.
The 9-bit method was introduced shortly after the market launch of the S7-3001).
However, to ensure downward compatibility, new CPUs are still capable of the 8-Bit method.
Systeme Helmholz modules all use the reliable 9-Bit method when possible.
However, there are modules possessing just the 8-Bit method on the market. To ensure reliable data transmission on the backplane bus and avoid incorrect switching, we advise against using such modules. The presence of 8-Bit modules can be seen by the shining of the red 8-Bit LED of the placeholder module.

1) S7-300 is a registered trademark of Siemens AG


  • Dummymodule, 20-way
  • Dummymodule, 40-way