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Running all your I/O in one central rack works until the cable runs get long. A machine 50 meters from the control cabinet means 50 meters of wire per sensor — expensive copper, voltage drop on analog signals, and a wiring nightmare during commissioning. ET 200SP solves this by putting the I/O where the field devices are and connecting back to the S7-1500 CPU over a single PROFINET cable.
Below: how ET 200SP works with S7-1500, which modules are available, how to select BaseUnits, and when distributed I/O makes more sense than centralized S7-1500 racks.
What is ET 200SP?
ET 200SP is Siemens' compact distributed I/O system. It connects to an S7-1500 CPU (or any PROFINET controller) over standard Ethernet. Each ET 200SP station consists of:
- Interface module (IM 155-6): The PROFINET head unit. It handles communication with the CPU and manages the local I/O modules.
- I/O modules: Digital input, digital output, analog input, analog output, safety, motor starters, IO-Link masters, and more.
- BaseUnits: Mounting bases that snap onto the DIN rail. Each I/O module plugs into a BaseUnit. The BaseUnit carries the backplane bus and provides terminal connections for field wiring.
- BusAdapter: A small component that plugs into the left side of the interface module. It defines the PROFINET connection type (RJ45, fiber, etc.).
- Server module: An end cap that terminates the station. Every ET 200SP station needs one at the right end.
From the S7-1500 CPU's perspective, the ET 200SP I/O modules appear in TIA Portal exactly like centralized I/O — you address them the same way. The PROFINET communication is transparent to your program.
Interface module options: IM 155-6
The interface module is the first component in every ET 200SP station. Siemens offers three main variants:
| Variant | Part Number Prefix | Key Feature | Best For |
|---|---|---|---|
| IM 155-6 PN ST | 6ES7155-6AU01-0BN0 | Standard performance, 1 PROFINET port | Cost-optimized stations, star topology |
| IM 155-6 PN HF | 6ES7155-6AU01-0CN0 | High Feature — media redundancy, prioritized startup, I-device | Production lines requiring network redundancy (MRP) |
| IM 155-6 PN HA | 6ES7155-6AU30-0CN0 | High Availability — system redundancy (S2), seamless failover | Continuous processes (chemical, power, water treatment) |
For most machine-building applications, the IM 155-6 PN ST is sufficient. It supports up to 64 modules per station and handles the full range of ET 200SP I/O modules including safety modules.
The HF variant adds media redundancy protocol (MRP) for ring topologies — important in production lines where a single cable break should not take down the entire network. The HA variant is for process automation with S7-400H or S7-1500R redundancy controllers.
BusAdapter: the PROFINET connection
Every IM 155-6 requires a BusAdapter plugged into its left side. The BusAdapter determines the physical PROFINET connection type:
| BusAdapter Type | Connection | Use Case |
|---|---|---|
| BA 2xRJ45 | Two RJ45 ports (integrated switch) | Standard Ethernet cabling, daisy-chain or star |
| BA 2xFC | Two FastConnect ports | Siemens FastConnect (tool-free) cable system |
| BA 2xSCRJ | Two SC-RJ fiber ports | Long distances, EMI-heavy environments |
| BA Send/Receive | Two LC fiber ports | Single-mode fiber for very long runs |
The 2xRJ45 BusAdapter is the default choice. The two ports allow daisy-chaining — connect one port to the upstream switch or CPU, and the second port to the next ET 200SP station or PROFINET device.
I/O module categories
ET 200SP supports a wide range of I/O modules. Here are the main categories.
Digital input modules (DI)
Available in 4, 8, 16, and 32-channel variants. Standard voltage is 24 VDC. High-feature (HF) versions support individual channel diagnostics (wire break, short circuit) — useful for critical sensors where you need to know immediately if a wire breaks.
Digital output modules (DQ)
We stock ET 200SP DQ modules including:
- 4-channel DQ module (6ES7132-6BF01-0BA0) — for applications needing per-channel isolation or higher current capacity
- 16-channel DQ module (6ES7132-6BH01-0BA0) — high-density output for solenoid banks, indicator lights, and relay coils
Transistor outputs switch 24 VDC loads directly. For AC loads or higher-power DC loads, use relay output modules or wire the transistor output to an external relay.
Analog input modules (AI)
Available in 2, 4, and 8-channel configurations. Support voltage (0-10V), current (4-20 mA), RTD (Pt100/Pt1000), and thermocouple measurements. High-speed variants offer update times as fast as 62.5 microseconds per channel — fast enough for vibration monitoring or dynamic pressure measurement.
Analog output modules (AQ)
Available in 2 and 4-channel variants. Output voltage (0-10V) or current (4-20 mA) signals to control valves, variable-speed drives, or proportional actuators.
Safety modules (F-DI / F-DQ)
Fail-safe I/O modules for SIL 3 / PL e safety applications. These communicate with S7-1500 F-CPUs over PROFIsafe. Use them for E-stop monitoring, safety door switches, safety light curtains, and safe motion inputs at remote stations.
Motor starters
Direct-on-line and reversing motor starter modules fit directly into the ET 200SP station. They replace the traditional contactor + overload relay combination with a compact electronic module that includes diagnostics, current monitoring, and parameterization via TIA Portal.
IO-Link master modules
IO-Link master modules bring smart sensors and actuators into the ET 200SP ecosystem. Each port connects one IO-Link device (smart sensor, valve terminal, RFID reader), allowing parameterization and diagnostics at the sensor level through TIA Portal.
BaseUnit types: a selection step you cannot skip
Every ET 200SP I/O module requires a BaseUnit. The BaseUnit determines the wiring type (screw or push-in terminals) and the electrical configuration (with or without auxiliary power bus). Choosing the wrong BaseUnit causes configuration errors in TIA Portal.
BaseUnit type codes
| Type Code | Meaning | When to Use |
|---|---|---|
| A0 | No AUX power bus connection | Analog modules, communication modules, any module that does not need the auxiliary power bus |
| A1 | AUX power bus connected (light-colored contacts) | Digital I/O modules where you want to distribute 24 VDC load power through the BaseUnit bus |
| B0 | New power group starts, no AUX connection | First module after an interface module, or to start a new isolated power group |
| B1 | New power group starts, AUX connected | First digital I/O module in a station or a new power group |
Rule of thumb: Start with a B1 or B0 BaseUnit (to begin the power group), then use A1 or A0 BaseUnits for subsequent modules in the same group. Use A0 for analog modules and A1 for digital modules.
Terminal types
- Screw terminals: Traditional screw-clamp connections. More familiar to electricians. Slightly slower to wire but easier to re-terminate.
- Push-in terminals: Spring-loaded connections — insert the wire and it locks. Faster wiring, vibration-resistant. Preferred for new installations.
Both terminal types accept the same wire gauges (0.14–1.5 mm2). Choose based on your team's preference and plant standards. A single station can mix screw and push-in BaseUnits.
Configuration in TIA Portal
Adding an ET 200SP station to your S7-1500 project in TIA Portal follows these steps:
- Add the IM 155-6 to the network view. Drag the correct IM variant from the hardware catalog. Assign it a PROFINET device name and IP address.
- Insert I/O modules. Drag modules into the ET 200SP rack slots in the device view. TIA Portal automatically validates module compatibility and BaseUnit requirements.
- Assign I/O addresses. Each module gets a start address for its inputs or outputs. You can accept TIA Portal's auto-assignment or set addresses manually to match your program structure.
- Configure module parameters. Set channel-specific options like input filter times, diagnostic enables, measurement ranges (for analog), and failsafe parameters (for F-modules).
- Download and assign device name. Compile the hardware configuration and download it to the CPU. Then assign the PROFINET device name to the IM 155-6 using "Online → Assign device name."
Once configured, the ET 200SP I/O addresses work identically to centralized S7-1500 I/O in your program. You can use the same I/O access instructions (A, =, L, T) regardless of whether the module is local or remote.
Station limits
| Parameter | Limit |
|---|---|
| Max modules per station | 64 |
| Max station width | ~1 meter (depending on module widths) |
| Max ET 200SP stations per S7-1500 CPU | Depends on CPU (32–256 PROFINET devices) |
| Max I/O data per station | 1024 bytes input + 1024 bytes output |
The 64-module limit is rarely reached in practice. A typical station has 8–20 modules. If you need more I/O in one area, use multiple ET 200SP stations on the same PROFINET network segment.
Centralized S7-1500 I/O vs. distributed ET 200SP
Both approaches work. The decision depends on your plant layout and project requirements.
| Factor | Centralized S7-1500 Rack | Distributed ET 200SP |
|---|---|---|
| Cable cost | High — individual cables from each sensor/actuator to the central panel | Low — one Ethernet cable per station, short field wiring at each station |
| Installation labor | Higher — long cable runs, large cable trays | Lower — small local junction boxes, short runs |
| Panel size | Large central panel with many terminal blocks | Smaller central panel + small distributed enclosures |
| Signal quality (analog) | Longer cable runs degrade analog signal accuracy | Short runs preserve signal quality; A/D conversion happens locally |
| Troubleshooting | All wiring in one place — easier to trace | Wiring distributed across the plant — but PROFINET diagnostics pinpoint faults remotely |
| Network dependency | No network required for I/O | I/O depends on PROFINET — network failure loses the station's I/O |
| Scalability | Limited by rack slots (32 modules max) | Add stations anywhere on the PROFINET network |
When to use centralized I/O
- All field devices are within 10 meters of the control panel
- I/O count is under 100 points
- You want the simplest possible architecture (no network for I/O)
When to use ET 200SP
- Field devices are spread across a large machine or multiple areas
- Cable runs would exceed 20 meters
- You need I/O in hazardous or space-constrained locations where a full S7-1500 rack will not fit
- You want hot-swap capability for individual I/O modules (ET 200SP supports this when configured)
- The total I/O count exceeds what one S7-1500 rack can handle
Many systems use both: centralized S7-1500 I/O for modules near the main panel, and ET 200SP stations for I/O that is physically distant.
Wiring an ET 200SP station
The physical wiring sequence for a new ET 200SP station:
- Mount the DIN rail in the local enclosure.
- Snap on BaseUnits in order: one per I/O module, starting from the left after the interface module position.
- Install the interface module on the leftmost BaseUnit. Plug in the BusAdapter on the left side.
- Install I/O modules onto their BaseUnits.
- Install the server module (end cap) on the rightmost BaseUnit.
- Wire field connections to the BaseUnit terminals — sensors, actuators, power feeds.
- Connect PROFINET via the BusAdapter ports.
- Connect 24 VDC power to the interface module and to the BaseUnit power group terminals.
One advantage of ET 200SP's design: the wiring stays on the BaseUnit. If a module fails, you pull the module off the BaseUnit and snap a replacement on — no rewiring needed. This is why ET 200SP supports in-service module swap.
Frequently asked questions
Can I mix ET 200SP and centralized S7-1500 I/O in the same project?
Yes. This is a common architecture. The S7-1500 CPU handles centralized I/O modules in its local rack and simultaneously acts as PROFINET I/O controller for one or more ET 200SP stations. In TIA Portal, both appear in the same project. Your user program accesses local and remote I/O with the same instructions — just different addresses.
What happens if the PROFINET cable to an ET 200SP station is disconnected?
The S7-1500 CPU detects the communication loss and sets the station's I/O to substitute values (configurable per module — typically 0 or last value). The CPU's BF (Bus Fault) LED turns on, and a diagnostic entry is written to the buffer. The rest of the system — including other ET 200SP stations — continues operating. When the cable is reconnected, the station automatically re-synchronizes.
Can I hot-swap a single ET 200SP I/O module while the station is running?
Yes, if the module and its BaseUnit are configured for hot-swap in TIA Portal. When you pull a module, the station continues operating — only the removed module's channels go to substitute values. Snap the replacement module (same type) onto the BaseUnit, and it automatically initializes with the configured parameters. No download or restart is needed. This is one of ET 200SP's key advantages over centralized S7-1500 I/O, which does not support hot-swap.
What is the maximum distance between the S7-1500 CPU and an ET 200SP station?
Using standard copper Ethernet (Cat5e/Cat6), the maximum distance is 100 meters per segment. With managed switches, you can extend this by adding switch hops — each hop adds another 100 meters. For longer distances without switches, use fiber optic BusAdapters: multimode fiber supports up to 3 km, and single-mode fiber supports up to 26 km. In practice, most industrial installations use copper within a building and fiber between buildings.
Build your distributed I/O system
We stock ET 200SP interface modules, I/O modules, BaseUnits, and BusAdapters. Browse our Siemens PLC Systems collection or view all Siemens products. Need help specifying a distributed I/O layout? Contact us with your I/O list and we will recommend the right configuration.