How-To Guide  ·  Siemens SIMATIC ET 200SP  ·  Distributed I/O System

ET 200SP: System Architecture, Module Selection, Configuration, and Migration Guide

Platform: SIMATIC ET 200SP  ·  Up to 32 I/O modules  ·  PROFINET IO / PROFIBUS DP  ·  TIA Portal / STEP 7

1. What Is the ET 200SP?

The ET 200SP is Siemens’ distributed I/O platform within the SIMATIC product family. It connects to the higher-level controller over PROFINET IO or PROFIBUS DP (depending on the interface module) and provides field-level signal conditioning for digital inputs, digital outputs, analog inputs, analog outputs, and specialty modules (communication, technology, motor starters). Siemens describes the design as scalable, so a station can be sized to local requirements, from a few modules up to the maximum configuration of the interface module (32 I/O modules with the IM 155-6 PN ST).

The ET 200SP is designed for cabinet-mounted distributed I/O applications where field devices (sensors, actuators, valves, motor starters) need to be connected close to the process rather than wired back to a central controller. Typical installations include:

• Manufacturing lines — conveyor I/O, packaging stations, assembly cells
• Process automation — valve terminal control, analog measurement, temperature monitoring
• Building automation — HVAC control, lighting, energy monitoring
• Water/wastewater — pump stations, remote valve control, level measurement

Key Platform Advantages

2. System Architecture

Every ET 200SP station is assembled from four component types, mounted left to right on a 35 mm DIN rail. The interface module connects to the controller network, BaseUnits provide field wiring terminals and power distribution, I/O modules process field signals, and a server module terminates the backplane bus at the right end.

Four-Component Breakdown

Station Assembly Order

1. Interface Module (leftmost). Mount the IM 155-6 on the DIN rail. Connect the PROFINET cable via the BusAdapter (RJ45 or M12) and supply 24 V DC power.
2. BaseUnit + I/O Module pairs. Slide BaseUnits onto the DIN rail to the right of the interface module, one per I/O slot. The first 24 V DC I/O module must sit on a light-colored BaseUnit so its potential group has a supply infeed. Subsequent BaseUnits can be dark-colored (same potential group) or light-colored (new potential group).
3. Snap I/O modules into BaseUnits. Each I/O module clicks into its BaseUnit, engaging the backplane connector automatically. The modules are self-coding: the first time a module is plugged in, part of its coding element clicks into the BaseUnit, so a different module type cannot be plugged into that slot afterward.
4. Server Module (rightmost). Install the server module at the last position to terminate the backplane bus. A missing server module causes a station stop.

3. Interface Modules

The interface module is the head of every ET 200SP station. It provides the network connection (PROFINET IO or PROFIBUS DP), distributes power from the 24 V DC supply to the backplane, and handles all communication with the upstream controller. Two PROFINET interface modules are compared below: the IM 155-6 PN ST (Standard, 6ES7155-6AU01-0BN0, also sold as the bundle 6ES7155-6AA01-0BN0) and the IM 155-6 PN/2 HF (High Feature, 6ES7155-6AU01-0CN0). Note that 6ES7155-6AA01-0BN0 is an ST module, not an HF module.

IM 155-6 PN ST vs. IM 155-6 PN/2 HF

BusAdapter Selection

The IM 155-6 PN ST uses a selectable BusAdapter that plugs into the front of the interface module. This allows you to choose the PROFINET connection independently from the interface module itself. The ET 200SP is an IP20 system intended for installation in a control cabinet, whichever BusAdapter is used.

4. BaseUnit Selection

Every I/O module in the ET 200SP requires a BaseUnit. The BaseUnit mounts to the DIN rail, provides push-in wiring terminals for field connections, and carries the self-assembling backplane bus (P1, P2, and AUX voltage rails) that distributes power across the station. Choosing the correct BaseUnit is critical — the width, color, terminal type, and AUX configuration must match the I/O module being installed.

BaseUnit Widths

Light vs. Dark BaseUnits

The ET 200SP uses a color-coded system to manage potential (voltage) groups within a station. This is one of the most important concepts in ET 200SP system design:

AUX Terminals

Some BaseUnit variants include AUX (auxiliary) terminals that provide additional potential distribution points. On the BU15 type A0 with AUX terminals these are 10 internally bridged terminals for individual use up to 24 V DC/10 A, or as protective-conductor terminals. BaseUnits are available with and without AUX terminals — select based on your wiring requirements.

BaseUnit and BusAdapter Part Numbers

5. I/O Module Overview

The ET 200SP platform offers a wide range of I/O modules for every application. Modules snap into BaseUnits and are organized by function: digital input (DI), digital output (DQ), analog input (AI), analog output (AQ), and specialty modules. The I/O modules are self-coding: on first insertion part of the module’s coding element clicks into the BaseUnit, so a different module type cannot be plugged into that slot afterward.

Digital Input Modules (DI)

For a detailed guide on the DI 16x24VDC ST module including wiring diagrams, TIA Portal configuration, and LED diagnostics, see our ET 200SP DI 16x24VDC Installation Guide.

Digital Output Modules (DQ)

Analog Input Modules (AI)

Analog Output Modules (AQ)

6. ET 200S vs. ET 200SP — Migration Guide

If you are searching for ET 200S part numbers such as 6ES7193-4CD30-0AA0, 6ES7151-3BA23-0AB0, or 6ES7138-4FB04-0AB0, you are looking at the older ET 200S platform. The ET 200S has been superseded by the ET 200SP, which is the current Siemens distributed I/O system. While the ET 200S is still supported, Siemens is actively directing new projects to the ET 200SP.

Platform Comparison

Common ET 200S to ET 200SP Part Number Mapping

Migration Considerations

1. Hardware is not interchangeable. ET 200S terminal modules and electronic modules cannot be used in an ET 200SP station, and vice versa. Migration requires replacing the entire station: interface module, BaseUnits, I/O modules, and server module.
2. Wiring is different. ET 200S uses screw or spring-clamp terminal modules. ET 200SP uses push-in BaseUnits. All field wiring must be re-terminated during migration.
3. Software migration. If your existing project uses STEP 7 V5.x, the IM 155-6 PN ST (6ES7155-6AU01-0BN0) can be configured with STEP 7 V5.5 SP4 or higher with HSP 0241 V4, or with TIA Portal V14 or higher (HSP 205). Some functions need newer engineering versions; check the interface module manual.
4. Address mapping. I/O addresses will change during migration. Update all PLC program references (inputs, outputs, diagnostics) to match the new module address assignments.
5. Potential groups. ET 200S uses PM-E power modules to start potential groups. ET 200SP uses light-colored BaseUnits. Map your existing power module positions to light-colored BaseUnit positions in the new layout.

7. Technical Specifications

Interface Module IM 155-6 PN ST (6ES7155-6AU01-0BN0)

BaseUnit Specifications

General Station Limits

8. Power Supply & Wiring

The ET 200SP requires 24 V DC power (SELV/PELV) for both the interface module (backplane electronics) and the field-side I/O modules. Power enters the station at two points: the interface module power terminals and each light-colored BaseUnit that starts a potential group.

Power Supply Requirements

Voltage Group Concept

A potential group (also called a voltage group) consists of all directly adjacent I/O modules that share a common field supply voltage. The potential group:

1. Begins at a light-colored BaseUnit, which interrupts the P1, P2, and AUX voltage buses from the left and requires its own L+ and M infeed.
2. Continues through consecutive dark-colored BaseUnits, which pass the P1, P2, and AUX buses through from the left neighbor.
3. Ends at the last dark-colored BaseUnit before the next light-colored BaseUnit or server module.

Wiring Best Practices

9. PROFINET Configuration

The ET 200SP station appears as a PROFINET IO device on the network. The upstream controller (S7-1500, S7-1200, etc.) acts as the PROFINET IO controller and manages the ET 200SP station. Configuration is performed in TIA Portal (STEP 7).

Basic TIA Portal Setup

1. Create a new project in TIA Portal and add your controller (e.g., S7-1500 CPU).
2. Open Devices & Networks view. The controller appears with its PROFINET interface.
3. Add the ET 200SP station. From the Hardware Catalog, expand Distributed I/O → ET 200SP → Interface modules. Drag the IM 155-6 PN ST (or HF) onto the network view.
4. Connect to the controller. Draw a PROFINET connection from the controller’s PROFINET port to the ET 200SP interface module. TIA Portal automatically assigns an IP address and device name.
5. Open the Device View of the ET 200SP station by double-clicking the interface module. This shows the station rack with empty slots.
6. Add I/O modules. From the Hardware Catalog, drag digital, analog, or specialty modules into the station slots. TIA Portal automatically assigns I/O addresses.
7. Configure module parameters. Select each module and configure its properties (input delays, diagnostics, channel activation) in the Properties panel.
8. Assign the PROFINET device name. Each ET 200SP station needs a unique PROFINET device name. Set this in the IM properties, then assign it to the physical device using Online → Assign PROFINET device name.
9. Download to the controller. Compile the project and download to the CPU. The controller will establish the PROFINET connection to the ET 200SP station.

PROFINET Device Name Assignment

Before the controller can communicate with the ET 200SP station, the physical interface module must be assigned a PROFINET device name that matches the name configured in the TIA Portal project. This is done once during commissioning:

10. Installation & Mounting

The ET 200SP mounts on standard 35 mm DIN rail per EN 50022. The station is assembled left to right and requires proper mechanical assembly before power-up.

Installation Steps

1. Mount the DIN rail. Use a 35 × 7.5 mm or 35 × 15 mm rail to EN 60715 (or a SIMATIC system rail). Ground the rail separately unless it is mounted on grounded, zinc-plated mounting plates. Where the station sees increased vibration and shock, fasten the rail about every 200 mm. Keep at least 20 mm free above the station and 10 mm at the left and right ends for installing and removing modules.
2. Install the interface module. With the supply voltage off, hook the IM 155-6 onto the rail and swivel it back until the rail release clicks into place. Screw the BusAdapter onto the front of the interface module (3 to 3.5 mm screwdriver).
3. Install BaseUnits. Mount each BaseUnit on the rail to the right of the interface module (or the previous BaseUnit) and slide it left until it latches. Place a light-colored BaseUnit at the start of each potential group.
4. Install the server module. Hook the server module (6ES7193-6PA00-0AA0) onto the rail to the right of the last BaseUnit, swivel it back, and slide it left until it latches onto the last BaseUnit. It completes the station and also holds 3 spare fuses.
5. Wire field connections. Connect field wiring to the BaseUnit push-in terminals. Wire the L+ and M supply at each light-colored BaseUnit.
6. Plug in I/O modules. Insert each I/O module parallel into its BaseUnit until both latches click. Coding is automatic: the coding element on each I/O module transfers to the BaseUnit the first time the module is plugged in, so the slot then only accepts a matching module.
7. Apply color identification labels (optional). The module-specific color identification labels are ordered as accessories; the color code printed on each module tells you which label it takes.
8. Connect PROFINET and power. Connect the PROFINET cable to the BusAdapter and plug the 24 V DC connector into the interface module.

Mounting Orientation

11. Troubleshooting

Interface Module LED Indicators

I/O Module LED Indicators

Common Problems and Solutions

12. Related Guides & Resources

Related PLC Exchange How-To Guides

Siemens Reference Documentation