Distributed I/O in SIMATIC S7

The SIMATIC S7 continues the trend towards greater decentralization through the integration of distributed I/O in the programmable controller.

This development is shifting from "distributed automation" to "open system distributed automation". Open system distributed automation splits the overall system into functional units, which process subtasks autonomously and interchange data. The functional units are controlled by devices that have "intelligence" - in other words, they can be programmed. This includes, for example, the I/O stations SIMATIC ET 200S and ET 200X.

The degree of system integration of the programmable controller and distributed I/O become apparent to the user in the:

• Uniform configuring;
  both the central and the distributed I/Os are configured with STEP 7. For the user, this means a uniform configuration tool independent of the type of configuration of the automation solution
• Centralized and distributed programming;
  the automation system is programmed with STEP 7 independently of the configuration type. This allows programs to be created without taking account of later hardware configuration.
• Centralized and distributed full system performance;
  SIMATIC S7 provides powerful system support including software-parameterizable I/Os, a wide range of diagnostics options and simple connection of function modules.
• Uniform diagnostics principle;
  from installation to start-up, and all the way through to regular operation; using the BT 200 bus tester or the diagnostic functions of STEP 7 or the I/O devices
• Programming, testing and startup via PROFIBUS DP;
  distributed automation structures require distributed start-up options. With STEP 7, programming, diagnosis and start-up of the central controller can be performed from the field in exactly the same manner as via the central programming interface of the CPU
• Integral PROFIBUS DP interface;
  the DP master interface is already integrated into many of the central modules. This saves on slots and costs and enables optimum performance.
• Uniform operation and monitoring;
  the SIMATIC S7 and SIMATIC Operator Panel work together ideally during configuration and operation. It is of no consequence here whether the bus stations are connected to the central programming interface (MPI) or to PROFIBUS DP
• Signalling of control diagnostics in the form of system events from the PLC to higher-level HMI devices ("signal system error" in STEP 7)

PROFIBUS demonstrates its system-wide integration in particular by its direct connection of field devices to PROFIBUS PA in process engineering applications. The process data can be passed on by DP/PA couplers directly to PROFIBUS DP and from there to the control level.

PROFIBUS DP V1

The following tables show the standardized extensions for a DP slave of DP master conforming to DP V1 as opposed to devices conforming to PROFIBUS DP: