Configuring S7-1500H Redundant System with ET200SP Stations

1. Overview: S7-1500H Redundant System Architecture

The SIMATIC S7-1500H is a high-availability redundant controller platform built on two identical CPUs operating in parallel as a primary/backup pair. Unlike the S7-1500R (which uses PROFINET system redundancy S2 only), the S7-1500H extends support to PROFINET system redundancy R1 devices beginning with firmware V3.0 and adds switched S1 device capability for non-redundant IO. This makes the H-system the most flexible target when migrating from three conventional S7-1500 CPUs with shared ET200SP stations to a fully redundant controller pair.

The S7-1500H backplane (UR2-H or UR2-HF aluminum mounting rail) hosts two CPUs of the same type (e.g., CPU 1517H-3 PN, CPU 1518H-4 PN/DP). Both CPUs run identical user programs synchronized via a fiber-optic redundancy link (Sync-Link 1 and Sync-Link 2). Each CPU maintains an independent PROFINET interface (X1) for IO communication and an additional interface for the sync cable.

2. PROFINET System Redundancy Modes Supported by S7-1500H

The S7-1500H controller pair operates as a single PROFINET IO controller from the perspective of the IO device. The IO device communicates with only one of the two CPUs at any given moment, while the backup CPU remains hot-standby with up-to-date IO image thanks to the MRP/MRPD redundancy mechanism. The available IO-device categories are:

Per the official SIMATIC S7-1500 S7-1500R/H redundant system manual, section 4.3.2 "Redundancy", the H-CPU supports S2 devices, R1 devices (FW V3.0 and higher), and standard IO devices via the switched S1 mechanism. The S2 and R1 modes tolerate errors in the direct IO-controller-to-IO-device communication path, whereas the switched S1 mode does NOT tolerate an interruption; the S1 device will fail and require re-establishment after a CPU switchover.

3. Hardware Prerequisites for S7-1500H with ET200SP

3.1 CPU Selection

Verify the firmware version actually installed using TIA Portal (Online > Accessible Devices > Read diagnostic information) before commissioning; field upgrades to FW V3.x should follow Siemens' firmware update guidelines and require both CPUs to be updated identically.

3.2 ET200SP Interface Module IM155-6PN HF

The interface module referenced in the source (6ES7 155-6AU01-0BN0) is the IM155-6PN HF (High Feature) for ET200SP. This IM is S2-capable as of firmware V3.0 and remains the recommended IO-device partner for the S7-1500H.

For PROFINET system redundancy R1 on ET200SP, an R1-capable IO device must be used. The IM155-6PN HF itself supports S2 (preferred) but R1 is generally reserved for compact IO devices such as ET200AL IM157-1 PN or specific field devices. Confirm R1 support in the device GSD file or via the official ET200SP IM155-6 PN HF manual.

4. Migration Path: From Three Conventional S7-1500 CPUs to One S7-1500H Pair

The original installation uses three standard S7-1500 CPUs with several ET200SP remote stations. Replacing the three CPU pair with one S7-1500H pair preserves the ET200SP stations provided they are S2-capable. The migration sequence is:

1. Inventory all existing ET200SP interface modules and verify that the IM order numbers are 6ES7 155-6AU0x-0BN0 (HF variants). Update any 6ES7 155-6AA00-0BN0 (ST) or older IMs to the HF variant.
2. Verify each IM is running FW V3.0 or higher. Older firmware versions (V1.x, V2.x) do not support PROFINET S2 system redundancy.
3. Verify the existing PROFINET topology. ET200SP HF IMs include a 2-port integrated switch which permits line topology; for S7-1500H, both CPUs must reach the IO device through independent paths. If the existing topology is a single line, you must restructure into a ring (MRP) or a dual-star to provide two separate PROFINET paths.
4. Replace the three S7-1500 CPUs with two S7-1500H CPUs of identical MLFB and FW on the UR2-H/UR2-HF mounting rail.
5. Configure both CPUs as a redundant pair in TIA Portal under Devices & Networks; assign the Sync-Link cable ports and configure the redundancy parameters.
6. Re-download the project to both CPUs.

5. PROFINET Topology: Configuring H-CPUs with PROFINET Rings and R1 Devices

The official Siemens application guide Configuring H-CPUs with PROFINET rings and R1 devices provides the canonical procedure for deploying R1 devices in a ring topology attached to an S7-1500H pair. The high-level architecture is:

• Both H-CPUs connect to a ring of managed PROFINET switches (e.g., SCALANCE XC/XR/XB series).
• The ring is configured as an MRP master / MRP client domain. One switch is the MRP manager; the remaining nodes are MRP clients.
• R1 IO devices sit on the ring; each R1 device has a single PROFINET port that connects to the ring.
• MRPD (Media Redundancy with Duplicate Frame) ensures both CPUs can send frames to the R1 device simultaneously. The device processes only the first-arriving valid frame.
• When the primary CPU fails, the backup CPU takes over the IO controller role. Because MRPD was already delivering duplicate frames, no re-parameterization is required - the R1 device continues operation seamlessly.

5.1 Topology Diagram (Inline SVG)

5.2 Step-by-Step Ring Configuration

1. In the TIA Portal project, open Devices & Networks and place the two H-CPUs on the UR2-H rail.
2. Add managed PROFINET switches (e.g., SCALANCE XC208) to the project and connect each H-CPU's X1 port to a switch in the ring.
3. Open the topology view and interconnect the switches into a closed ring. Right-click the ring nodes > Assign MRP Domain > configure one switch as MRP Manager, the others as MRP Client.
4. Place the R1 IO devices on the ring nodes. In the IO device properties, set the "PROFINET system redundancy" dropdown to R1. This is only available for H-CPUs with FW V3.0 or higher.
5. Assign IO modules to the R1 device and configure update times. The recommended update time for R1 is 1 ms (RT class 1 / IRT).
6. Compile and download. Both H-CPUs will send duplicate IRT frames to the R1 device simultaneously; the device accepts the first valid frame.

6. Switched S1 Device Function for Legacy ET200SP Stations

When ET200SP IMs without S2 capability must be retained (for example, ST-series IMs in legacy installations), the S7-1500H provides the switched S1 device function. The CPU temporarily activates the S1 IO device, acquires its IO, then releases it; on switchover, the device drops out and must re-attach.

Configuration in TIA Portal:

1. In Devices & Networks, drag the legacy ET200SP IM into the project.
2. Open the IM properties > PROFINET interface > "IO redundancy" tab.
3. Select "Switched S1 device" from the redundancy mode dropdown.
4. Assign the IM to one of the H-CPU's PROFINET interfaces. Only the active CPU owns the device; the standby CPU does not maintain a permanent AR (Application Relationship) to the S1 device.
5. Compile and download. The IM will cycle through STOP/RUN transitions during a CPU switchover. Expect a 1-3 second process IO update gap depending on PROFINET update time.

7. TIA Portal Project Configuration

7.1 Project Setup

• Open TIA Portal V17 or later (V18 recommended for FW V3.1 H-CPUs).
• Create a new project and add the two H-CPUs from the Hardware Catalog > SIMATIC S7-1500 > CPU > S7-1500H.
• Both CPUs are placed on the same UR2-H mounting rail. The two sync-link ports (X3 for CPU 1517H) must be connected with a fiber-optic cable (LC duplex, OM2/OM3 multimode).

7.2 Redundancy Parameters

In the H-CPU properties, configure the following redundancy-relevant parameters:

8. Program Synchronization and Organization Blocks

On the S7-1500H, the user program runs identically on both CPUs. The firmware keeps code, data blocks, and process image aligned through the sync-link. Special OBs to implement for redundancy-aware behavior:

Sample ST code (in OB 72) to log redundancy state changes:

IF #EV_CLASS = 16#13C0 THEN  // redundancy lost
    "logDB".redundancyState := 0;
    "logDB".lastEvent := 'REDUNDANCY_LOST';
ELSIF #EV_CLASS = 16#13C1 THEN  // redundancy restored
    "logDB".redundancyState := 1;
    "logDB".lastEvent := 'REDUNDANCY_OK';
END_IF;

9. Commissioning and Verification

1. Power up both CPUs; observe both LED states. STATUS LED should be solid green; REDUNF LED should be off once pairing is established.
2. Check the online diagnostic view in TIA Portal: both CPUs should report "RUN, redundancy OK".
3. Force a CPU switchover test: from TIA Portal, right-click the standby CPU > "Switch to master" (or use the SIMATIC Automation Tool). Verify that process IO remains live with no step change in process values.
4. Pull the sync-link fiber cable. Both CPUs should transition to STOP after the configured sync-link loss timeout (default 500 ms). Reconnect; verify redundancy is re-established.
5. Pull an S2 IO device's PROFINET cable. The active CPU should log an OB 86 (rack failure); the IO device should reconnect when the cable is restored.
6. For R1 ring testing, break a single ring segment. MRP should reconfigure within <200 ms; R1 IO devices should remain online via the alternate path.

10. Troubleshooting Matrix

11. Key Field-Engineering Constraints and Best Practices

• Identical pairing: Both H-CPUs must have identical MLFB, identical firmware, and identical configuration. Any mismatch forces the system to enter STOP with diagnostic buffer entry "Redundancy pairing not possible".
• Sync-Link cable length: Maximum sync-link length is 10 m with standard LC-LC multimode fiber. For greater distances, use the sync-link extender (6ES7 656-7DX00-0XX0) which supports up to 40 km via dark fiber.
• Mixing R1 and S2: You can mix S2 and R1 devices on the same H-CPU; however, R1-capable IMs must be deployed in a ring topology while S2 devices can be in line or star.
• OB execution: OB 1 (main), OB 82, OB 83, OB 86 run identically on both CPUs. OB 72 fires only on the CPU that owns the redundancy event. Avoid non-deterministic code in OB 1 (no time-of-day functions, no ASIO calls) to maintain cycle determinism.
• Stop behavior: If only one CPU enters STOP, the partner CPU continues running as a single CPU (without redundancy). The process continues without interruption but at reduced availability. Restart the failed CPU as soon as possible to restore redundancy.
• Firmware updates: Update both CPUs in sequence, one at a time, while the partner CPU continues to run. Never attempt simultaneous firmware updates.
• GSD files: Always import the latest GSD/GSDML for IO devices. Siemens typically releases GSD updates coincident with firmware releases that enable new redundancy features.
• Diagnostic buffer hygiene: Keep OB 72 short - heavy logic in OB 72 will lengthen redundancy switchover time and could violate the configured sync-loss watchdog.

12. Related Siemens Manuals and References

• SIMATIC S7-1500 S7-1500R/H redundant system system manual - authoritative reference for redundancy modes, sync-link behavior, and OB semantics.
• Configuring H-CPUs with PROFINET rings and R1 devices - official TIA Portal step-by-step procedure for ring topology with R1 IO.
• ET200SP IM155-6 PN HF manual - reference for the 6ES7 155-6AU01-0BN0 interface module, including S2 capability and firmware history.
• PROFINET System Redundancy S2 application manual - extended application guide for S2 device integration.

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