Overview
The SIMATIC ET 200MP is a modular, scalable distributed I/O system designed to connect process signals to a higher-level controller (typically a SIMATIC S7-1500 or S7-1200 CPU) over PROFINET or PROFIBUS. ET 200MP shares its I/O module catalog with the S7-1500 central rack, which means any signal module qualified for the S7-1500 can be installed in an ET 200MP station using a compatible interface module (IM).
Selection of an ET 200MP station involves four recurring decisions:
- Which interface module (IM 155-5 PN ST, IM 155-5 PN HF, IM 155-5 DP ST) to use.
- Which power option to install (system power supply PS, power module PM, or third-party 24 VDC).
- Which digital, analog, and special function modules to populate the slots with.
- How many U connectors are required to mechanically and electrically link the modules and the PS/IM.
This reference consolidates the official Siemens guidance on each of these decisions, including the digital output relay modules that are frequently missed in catalog searches dominated by 24 VDC transistor outputs.
ET 200MP Architecture and Topology
According to the Siemens product description, the ET 200MP distributed I/O system is a scalable and flexible distributed I/O system for connection of process signals to a central controller via a field bus (SIMATIC ET 200MP - Siemens product page). An ET 200MP station consists of:
- An Interface Module (IM) terminating the PROFINET or PROFIBUS subnet.
- Optional System Power Supply (PS) modules (e.g., PS 25W 24VDC, PS 60W 24/48/60VDC) that provide the backplane with 5 VDC and 24 VDC for the I/O modules.
- I/O modules from the S7-1500 catalog, mounted on a shared DIN rail and connected by U connectors.
- A load current supply (typically 24 VDC from a SITOP or third-party power supply) for the field-side actuator and sensor power.
The interface module and the I/O modules communicate over the integrated backplane bus. In ET 200MP, the backplane bus is implemented through U connectors that bridge adjacent modules, not through a fixed active backplane like ET 200M with active backplanes.
Power Options: PS, PM, and Third-Party 24 VDC
Three power scenarios are commonly considered for an ET 200MP station:
| Option | Function | U Connector Required | Typical MLFB |
|---|---|---|---|
| System Power Supply (PS 25W / 60W / 60W 24/48/60VDC) | Provides internal backplane voltages (5 VDC, 24 VDC) to power I/O module electronics. | Yes - 1 x 6ES7590-8AA00-0AA0 on the left side of the PS |
6ES7505-0KA00-0AB0, 6ES7505-0RA00-0AB0, 6ES7505-0RB00-0AB0 |
| Power Module (PM 70W 120/230VAC, PM 190W 120/230VAC) | Diagnostic-capable feed-in for 24 VDC load current only; does not inject power into the backplane. | No - the PM sits in the I/O row but does not require a U connector | 6ES7505-0CA00-0AB0, 6ES7505-0DA00-0AB0 |
| Third-party 24 VDC power supply | Replaces the PS/PM at the system level. Supplies the backplane via the I/O modules' 24 VDC terminals or via a PM if a clean diagnostic point is required. | Depends on whether a PS-equivalent is in the slot | SITOP PSU100M/PSU200M, Phoenix Contact, Puls, etc. |
A common configuration mistake is treating PS and PM as interchangeable. They are not:
- PS modules regenerate and monitor the backplane. Removing a PS disconnects downstream modules from the backplane bus.
- PM modules are simply 24 VDC feed-in / diagnostic points for the load voltage. They do not break the backplane bus when removed, and they do not require a U connector on the left side.
A third-party 24 VDC supply can substitute for a Siemens PS provided the supply meets the ET 200MP tolerance window (typically 19.2 V to 28.8 V at the module terminals, SELV/PELV, and adequate inrush/hold-up margin for the I/O module current budget). The official ET 200MP / S7-1500 system manual (SIMATIC S7-1500 / ET 200MP System Manual, entry ID 86140384) lists the electrical and mechanical requirements for the load-voltage source.
U Connectors: Quantity, MLFB, and Placement
The U connector is the mechanical and electrical bridge between two adjacent ET 200MP/S7-1500 modules. It carries the backplane bus contacts and is inserted into the left side of every I/O module that needs to communicate with the IM or PS on its left.
| U Connector Variant | MLFB | Used On |
|---|---|---|
| Standard U connector, 5 units | 6ES7590-0AA00-0AA0 | All standard I/O modules (DI, DQ, AI, AQ, F-modules, technology modules, communications modules). Also used on the PS. |
| U connector for PS (left-side slot, may be referenced separately in older catalogs) | 6ES7590-8AA00-0AA0 | Left side of a System Power Supply module. |
Quantity rule:
- One U connector ships inside the packaging of every S7-1500 / ET 200MP I/O module sold through the Siemens catalog.
- The first slot to the right of the IM uses the U connector that arrived with that first I/O module. The U connector plugs into the left side of the module and engages the backplane contacts of the previous device (IM or PS).
- Every additional I/O module in the row reuses the U connector from its own packaging. It plugs in on the left side and bridges to the previous module.
- The last I/O module in the row does not need a U connector on its right side. It is intentionally open.
- The interface module does not ship with a U connector; the first U connector comes from the first I/O module or the PS (if present).
- PM modules do not consume a U connector slot.
Digital Output Relay Modules Available for ET 200MP
ET 200MP does offer relay output modules, although they are not surfaced by every catalog filter that defaults to "24 VDC transistor." The two production modules qualified for the S7-1500 / ET 200MP catalog are:
| Module | MLFB | Channels | Contact Rating | Diagnostic / Function Class |
|---|---|---|---|---|
| DQ 16x230VAC/2A ST Relay | 6ES7522-5HH00-0AB0 | 16 relay outputs, isolated in groups | 230 VAC / 2 A per channel, 8 A per group | ST (Standard) - per-channel diagnostic, value status |
| DQ 8x230VAC/5A ST Relay | 6ES7522-5HF00-0AB0 | 8 relay outputs, isolated | 230 VAC / 5 A per channel, 8 A per group | ST (Standard) - per-channel diagnostic, value status |
Documentation:
- SIMATIC S7-1500/ET 200MP DQ 16x230VAC/2A ST Relay - manual, entry ID 109475445
- SIMATIC S7-1500/ET 200MP DQ 8x230VAC/5A ST - manual, entry ID 59192915
Both modules use the same mechanical form factor as the standard 24 VDC DQ modules. They are inserted into the ET 200MP backplane using a U connector on the left side, exactly like a transistor DQ module. They differ only in the field wiring (230 VAC switching versus 24 VDC switching) and in the absence of a high-side driver; instead each channel is a dry-form-A (normally open) contact.
BA vs ST vs HF Module Classes
S7-1500 / ET 200MP signal modules are graded by their function scope. The three suffixes encountered in MLFBs are BA, ST, and HF. The same convention applies to the interface modules (IM 155-5 PN ST vs. PN HF) and to the CPUs (CPU 1511-1 PN vs. CPU 1515-2 PN vs. CPU 1518-... PN/DP).
| Class | Name | Function Scope | Typical Use |
|---|---|---|---|
| BA | Basic | Minimum feature set. No value status (QI), no extended diagnostics, no isochronous mode, no oversampling, no channel-granular parameter reassignment. Lowest price point per channel. | Cost-optimized digital and analog I/O for standard PLC tasks. |
| ST | Standard | Adds value status (QI), per-channel diagnostics, isochronous mode support on most ST modules, hardware interrupts on rising/falling edges, and (for analog) extended measurement ranges, scaling, and basic diagnostics. | Default choice for most ET 200MP stations. Covers >80% of mainstream applications. |
| HF | High Feature | Full feature set. Adds fast oversampling, nanosecond-stamped interrupts where supported, full isochronous capability, value status, advanced diagnostics, and additional functions such as frequency measurement, PWM, pulse generation on DQ HF modules, and high-resolution analog conversion. | Motion, high-speed counting, precision measurement, and applications needing oversampling or sub-millisecond deterministic I/O. |
Examples of HF modules in the S7-1500/ET 200MP catalog include:
- DI 32x24VDC HF (6ES7521-1BL00-0AB0)
- DQ 16x24VDC/0.5A HF (6ES7522-1BH00-0AB0)
- AI 8xU/I/RTD/TC ST (6ES7531-7KF00-0AB0) - the analog ST module is the typical "value-status-capable" analog module, while the AI 8xU/I/RTD/TC HF (6ES7531-7PF00-0AB0) adds 1 ppm precision, oversampling, and value status.
Step-by-Step: Building an ET 200MP Station with an S7-1200 Controller
The following procedure applies the selection rules above to a small ET 200MP station controlled by an S7-1200 CPU (e.g., CPU 1215C) over PROFINET. The S7-1200 is the controller; the ET 200MP is the distributed I/O island.
- Pick the interface module. Use the IM 155-5 PN ST (6ES7155-5AA00-0AB0) for most S7-1200-coupled stations. The IM 155-5 PN HF (6ES7155-5BA00-0AB0) is only required if the application needs isochronous PROFINET, more than the ST port count, or media redundancy (MRP) as a client.
- Decide on the power option. For a small station with 4 to 8 I/O modules, a single PS 25W 24VDC (6ES7505-0KA00-0AB0) is typically sufficient. Drop the PS and rely on a SITOP or third-party 24 VDC at the module terminals if the field-side supply is already conditioned and the backplane current budget is within the IM's own feed-in capability.
- Choose I/O modules. For mixed I/O, a common minimal build is: DI 16x24VDC ST (6ES7521-1BH00-0AB0), DQ 16x24VDC/0.5A ST (6ES7522-1BH00-0AB0), and AI 4xU/I/RTD ST (6ES7531-7QD00-0AB0) for thermocouple or 4-20 mA inputs. Add a DQ 8x230VAC/5A ST relay (6ES7522-5HF00-0AB0) if any 230 VAC load must be switched.
-
Count U connectors. Count the I/O modules plus the PS (if used) and confirm that the same number of
6ES7590-0AA00-0AA0connectors are in inventory. Each module ships with its own. Do not order the connector separately unless a spare is required. - Configure in TIA Portal. In the TIA Selection Tool or the TIA Portal device configuration, insert the IM from "ET 200MP" > "Interface modules" and then drag the S7-1500 signal modules into the slots. The TIA Portal will warn if an incompatible module is dragged in (e.g., a CPU into a distributed I/O slot).
- Assign PROFINET device name and IP. From the TIA Portal "Online > Accessible devices" or via PRONETA, assign the device name to match the configured name in the PROFINET topology editor.
- Wire the station. Connect the IM's PROFINET ports to the S7-1200's PROFINET port. Wire 24 VDC to the PS (or directly to the load-current terminals of the I/O modules if no PS is used). Wire the field-side I/O to the appropriate channel terminals.
- Download and verify. Compile the S7-1200 project, download to the CPU, and watch the IM's DIAG LED transition from red to green. In the TIA Portal "Online > Diagnostics," confirm that all modules appear with green status and that the configured value status (QI) bits toggle when the inputs are forced.
Verification Checklist
| Check | Expected Result |
|---|---|
| IM SF/DIAG LED after power-up | Green (steady) - no SF, no BF, no maintenance demand. |
| PROFINET connection (S7-1200 to IM 155-5 PN) | PROFINET device name resolved, AR established, no BF (bus fault) LED on the IM. |
| U connector seating | All U connectors fully inserted; no red "module not recognized" diagnostic in TIA Portal online view. |
| PS load current margin | Total I/O module 5 VDC / 24 VDC backplane current demand < 80% of PS rated output (per the System Manual, entry ID 86140384). |
| Relay output contact wear budget | For inductive loads, fit an RC snubber or varistor across the contact; estimate electrical life from the module's datasheet curves (operations vs. load current at 230 VAC). |
| Value status (QI) bits | For ST/HF modules, QI = 1 indicates the channel is configured and healthy. QI = 0 indicates a channel-level fault, wire break, or short circuit (where supported). |
Troubleshooting Matrix
| Symptom | Likely Cause | Action |
|---|---|---|
| IM SF LED red, "Station failure" diagnostic | Missing or improperly seated U connector between IM and the first I/O module | Power down, remove first I/O module, reinsert the U connector on its left side, remount. |
| IM recognizes only the first few modules | A U connector between two modules is missing or damaged | Re-seat the U connector at the boundary between the last-recognized and first-unrecognized module. |
| PS reported as "fault" but backplane is alive | Third-party 24 VDC supply out of tolerance or PS/PM confused in the slot | Verify 24 VDC at PS input terminals. Confirm the slot in TIA Portal matches a PS MLFB, not a PM MLFB (PMs do not inject backplane power). |
| Relay output does not switch under program control | Module is not a relay module (e.g., 24 VDC transistor selected by mistake) or value status is 0 | Confirm the MLFB ends in ...5HH00-0AB0 (16x230VAC/2A) or ...5HF00-0AB0 (8x230VAC/5A). Check QI in the TIA Portal watch table. |
| PROFINET station goes into "station stop" intermittently | PROFINET name conflict, duplicate IP, or MRP misconfiguration | Use PRONETA to scan and reassign. Disable MRP on HF IM if the S7-1200 controller does not support MRP. |
Frequently Asked Questions
Does ET 200MP have relay digital output modules?
Yes. The two production relay modules qualified for ET 200MP are the DQ 16x230VAC/2A ST (MLFB 6ES7522-5HH00-0AB0) and the DQ 8x230VAC/5A ST (MLFB 6ES7522-5HF00-0AB0). They are part of the S7-1500 I/O catalog and slot directly into the ET 200MP backplane with a U connector.
How many U connectors are needed for an ET 200MP station?
One U connector (6ES7590-0AA00-0AA0) per I/O module plus one for the left side of any PS module. Every I/O module and PS ships with its own U connector, so the count for a normal build equals the number of I/O modules plus PS units. PM modules and the IM do not consume U connector slots.
Can a third-party 24 VDC power supply replace the Siemens PS?
Yes, provided the supply delivers 19.2 to 28.8 VDC at the module terminals (SELV/PELV) and can source the I/O module backplane and load-current budget. A Siemens PM (6ES7505-0CA00-0AB0 or 6ES7505-0DA00-0AB0) can be retained in the slot as a diagnostic feed-in even when a third-party supply is the primary source.
What is the difference between BA, ST, and HF signal modules?
BA (Basic) is the minimum-feature, lowest-cost option. ST (Standard) adds value status (QI), per-channel diagnostics, isochronous mode, and edge-triggered hardware interrupts. HF (High Feature) further adds oversampling, high-precision analog conversion, and full isochronous support, and is used for motion and high-speed applications.
Does the ET 200MP interface module ship with a U connector?
No. The IM 155-5 PN ST or HF interface module does not include a U connector. The first U connector in the row comes from the packaging of the first I/O module (or from the PS, if a PS is the first device in the row).