Configuring Siemens Y-Link with ET 200S in PCS 7 H Systems

Overview

A Siemens Y-Link is a redundant PROFIBUS DP gateway that allows remote I/O stations equipped with a single PROFIBUS interface to communicate with a redundant PCS 7 H station (AS). In the typical configuration, an engineer has multiple ET 200S distributed I/O stations — each fitted with an IM 151-1 interface module that exposes a single DP slave port — and must connect them to a SIMATIC PCS 7 automation system configured as a fault-tolerant H station. Because the H station exposes two redundant DP master interfaces and the ET 200S cannot itself terminate two PROFIBUS segments, a Y-Link built from two IM 153-2 interface modules in a shared ET 200M rack is inserted between the H system and the lower-level PROFIBUS segment that carries the ET 200S stations. The Y-Link presents one logical DP master to the ET 200S stations and two redundant DP slaves to the H system. This is the standard architecture recommended by Siemens for integrating single-interface PROFIBUS devices into H systems, as documented in Siemens Support entry 43688632 – How is the Y-Link structured?.

Y-Link Architecture and Operating Principle

The Y-Link consists of two IM 153-2 High Feature interface modules mounted in the same ET 200M rack. The two modules are joined through the backplane bus of the rack, and one of them acts as the active gateway (DP master toward the lower PROFIBUS segment) while the other remains in standby. The H station addresses both IM 153-2 modules as a single, redundant DP slave. The active IM 153-2 forwards all process data, diagnostics, and acyclic services to and from the lower PROFIBUS segment.

The key behavioral points of the Y-Link are:

• Both H-CPU DP masters continuously poll both IM 153-2 modules; only the active IM 153-2 returns valid process data and acyclic responses.
• Standby IM 153-2 is hot; on failure of the active module, the standby becomes the new active gateway within the configured monitoring time (default 100 ms, range 10 ms – 65535 ms).
• The lower PROFIBUS segment connected to the active IM 153-2 is a classic DP master segment. All ET 200S stations on this segment see a single DP master and exchange I/O data with the AS through the Y-Link.
• Diagnostic data from any ET 200S station is forwarded through the Y-Link to the H system and from there to the PCS 7 OS.
• The Y-Link itself supports PROFIBUS DP-V1 acyclic services; the ET 200S behind the Y-Link can be diagnosed using SFB 52 / SFB 53 (RDREC / WRREC) from the H-CPU through the Y-Link.

Hardware Requirements and Order Numbers

The Y-Link is built from standard ET 200M components. The recommended parts are:

For the ET 200S stations on the lower segment, the standard components are:

• IM 151-1 Standard (DP-V0) or IM 151-1 High Feature (DP-V1) — order numbers in the 6ES7151-1Axx or 6ES7151-1BAxx series. DP-V1 modules are recommended for full diagnostic support through the Y-Link.
• PM-E power module to feed the ET 200S backplane.
• Digital, analog, technology, and (optionally) F-modules from the ET 200S catalog.

Prerequisites for Configuration

Before starting the HW Config / PCS 7 engineering, ensure the following:

1. PCS 7 engineering station with SIMATIC Manager (PCS 7 V8.x or V9.x) or PCS 7 V10 in the TIA Portal. The Y-Link is part of the standard PCS 7 hardware catalog and is also available in STEP 7 HW Config.
2. H station type is configured for the AS. The two H-CPUs must be of an H-type (e.g., CPU 417-4H, CPU 412-5H, CPU 414-5H, CPU 416-5H, or current successors). Single CPUs cannot address a Y-Link redundantly.
3. PROFIBUS addresses for the H-CPU DP master interfaces are pre-planned. Typical H-CPU DP master 1 = PROFIBUS address 2, DP master 2 = PROFIBUS address 3.
4. Unique DP addresses for both Y-Link IM 153-2 modules (e.g., 4 and 5) and for each ET 200S station on the lower segment (e.g., 6, 7, 8). No two stations on the same physical PROFIBUS segment may share an address.
5. GSD file for IM 151-1 (ET 200S) installed in the engineering tool if using third-party GSD; Siemens ET 200S modules use the integrated catalog.
6. Bus parameters consistent across all PROFIBUS segments: 1.5 Mbps is the safe default for a Y-Link with three ET 200S stations. 12 Mbps is possible but tighten the slot time and reduce retries to avoid diagnostic nuisance.
7. Bus termination powered on at the first and last physical node on every PROFIBUS segment. The Y-Link's two IM 153-2 modules occupy slots that act as the start of the upper segments; the ET 200S at the end of the lower segment must have termination enabled.
8. Shielding and equipotential bonding in place; PROFIBUS cable shield clamped at every cabinet entry with the Siemens shielding bar (e.g., 6ES7390-5AA00-0AA0).

Configuring the Y-Link in HW Config (Step-by-Step)

The procedure below uses SIMATIC Manager / HW Config. The PCS 7 V10 in the TIA Portal uses the same logic, although the dialog titles differ slightly.

1. Open the PCS 7 project and the AS H station in HW Config.
2. Insert the H-CPUs (CPU 4xx-5H) in slots 3 and 4 of the AS rack. Connect PROFIBUS DP master interface 1 (X1) of CPU 1 to a DP master system, and PROFIBUS DP master interface 1 of CPU 2 to a second DP master system. These are the two upper PROFIBUS segments that the Y-Link will sit on.
3. In the hardware catalog, expand PROFIBUS DP > Network Components > Y Link. Drag the Y-Link onto each of the two DP master systems. You will be prompted to assign a DP address to each IM 153-2 — assign 4 to the left one and 5 to the right one (or as planned).
4. When prompted, set the redundancy role of the two IM 153-2 modules: usually the one on PROFIBUS master 1 of the first H-CPU is the left (active by default), and the one on PROFIBUS master 2 of the second H-CPU is the right (standby by default). The pairing is automatic once both Y-Link objects are inserted in the same project tree.
5. Open Object Properties > Y-Link on the active IM 153-2 and configure:
   • Diagnostic address: e.g., 16384 (use an address range outside the I/O address space).
   • Monitoring time: 100 ms (range 10–65535 ms). Shorter values detect failures faster but increase the risk of nuisance switches on temporary interference.
   • Behavior on lower-segment failure: Choose whether the H system should switch to the standby Y-Link or maintain the active one based on the configured criterion.
6. Compile the AS station and download the hardware configuration to both H-CPUs. The CPUs must be in STOP for the first download or use H-CiR / CiR if available.
7. On the lower PROFIBUS segment, the active IM 153-2 acts as a DP master. Drag each ET 200S station from the catalog onto this segment. Assign DP addresses 6, 7, 8 in order.
8. For each ET 200S, double-click the IM 151-1 to open its slot table and insert the actual I/O modules in the same order as the physical mounting (PM-E, then DI, DO, AI, AO, etc.). HW Config calculates the I and Q addresses automatically based on the slot.
9. Verify that the total process data on the lower segment does not exceed 255 bytes input and 255 bytes output (see section on the 255-byte limit).
10. Save, compile, and download to the H system.

Configuring ET 200S Stations on the Lower PROFIBUS Segment

Each ET 200S station must be configured as a DP slave on the lower segment of the Y-Link. The following parameters are field-proven starting points:

ET 200S vs ET 200M for Redundant PROFIBUS Integration

The question that often arises is whether ET 200M can be used in place of ET 200S to achieve the same redundancy goal. The answer depends on the application:

If the application needs direct redundant PROFIBUS without the Y-Link as an extra failure point, ET 200M with two IM 153-2 is the appropriate choice. If the application needs the bit-level density, F-modules, and the specific ET 200S module catalog (e.g., motor starters, technology modules), the Y-Link solution is the only practical way to integrate into an H system.

255-Byte Data Exchange Limit

The Y-Link limits the total process data exchanged between the lower PROFIBUS segment and the H station to 255 bytes of inputs and 255 bytes of outputs per Y-Link. This limit comes from the maximum payload of a single PROFIBUS DP cycle and is documented in Siemens Support entry 43688632.

To check whether three ET 200S stations fit, sum the input and output bytes of every module across the three stations:

Total_IN  = SUM (bytes_IN of all modules in ET 200S #1) +
            SUM (bytes_IN of all modules in ET 200S #2) +
            SUM (bytes_IN of all modules in ET 200S #3)

Total_OUT = SUM (bytes_OUT of all modules in ET 200S #1) +
            SUM (bytes_OUT of all modules in ET 200S #2) +
            SUM (bytes_OUT of all modules in ET 200S #3)

Constraint: Total_IN  <= 255 bytes
            Total_OUT <= 255 bytes

Typical module byte counts for ET 200S:

If the 255-byte limit is exceeded, the H station reports a configuration error and the Y-Link does not enter the active role. The HW Config log under Station > Consistency Check flags the overflow before download.

Redundancy Switching Behavior

Redundancy on the Y-Link is governed by the configured monitoring time and the diagnostic traffic on both upper PROFIBUS segments. The states and transitions are:

The H-CPU monitors the Y-Link through the configured diagnostic address. A Y-Link switchover is signalled to the application via OB 82 / OB 86 and via the standard diagnostic DB if the Y-Link is named in HW Config.

Diagnostics and Fault Handling

The Y-Link exposes diagnostics through the standard SIMATIC mechanisms. From the H-CPU and the PCS 7 OS, the following diagnostic paths are available:

1. PROFIBUS DP standard diagnostics on the H-CPU side. A station failure on either IM 153-2 raises OB 86 with the configured diagnostic address of the failed module.
2. Y-Link internal diagnostics on the lower segment. Each ET 200S station's diagnostic interrupt is forwarded to the H-CPU and surfaced in the PCS 7 OS as a module-level fault.
3. Module-level diagnostics using SFB 52 (RDREC) on the H-CPU. The diagnostic index 0x000A returns the IM 151-1 diagnostic record; the index 0x8000 series returns module-specific data.
4. Web server / FC of the H-CPU (CPU 4xx-5H with Ethernet PN interface): the integrated web server shows the redundancy status of the Y-Link under Module Information > Redundancy.
5. LEDs on the IM 153-2: SF (red) for group fault, BF (red) for bus fault on the upper segment, ACT (green) for active role, and a DC24V indicator for power supply health.

For a robust application, add the following blocks to the H-CPU user program:

• OB 82 – Diagnostic interrupt for module diagnostics (e.g., ET 200S module removed).
• OB 83 – Module insert/remove interrupt.
• OB 85 – Program execution error (e.g., I/O access to a failed station).
• OB 86 – Rack / station failure (Y-Link IM 153-2 lost or ET 200S station lost).
• SFB 52 RDREC and SFB 53 WRREC – Acyclic read/write of ET 200S module parameters (e.g., analog scaling, substitution values).

Commissioning and Verification

After HW Config is downloaded, walk through the following verification steps in order:

1. Power-on check: Both IM 153-2 power up. The ACT LED on the active module is on; the standby ACT LED is off or blinking (firmware-dependent). SF and BF LEDs are off on both.
2. PROFIBUS online: In HW Config, right-click the upper DP master system of each H-CPU and select PROFIBUS > Diagnostics > Node Status. Both Y-Link IM 153-2 modules appear with status OK; the active one shows the role Active.
3. Lower segment check: Open the active IM 153-2 properties and select PROFIBUS > Diagnostics for the lower segment. Each ET 200S station appears with its DP address and a green status indicator.
4. Process data test: Force a known value in the H-CPU and verify that it appears on the corresponding output of each ET 200S. Force a known input at the ET 200S terminal block and verify that the H-CPU process image updates.
5. Switchover test (planned downtime): Disconnect the upper PROFIBUS connector of the active IM 153-2. Within 100 ms (or the configured monitoring time), the standby becomes active. The H-CPU logs OB 86 for the lost module and OB 86 for the new active; the lower segment continues to run without interruption of process data.
6. Switchover restoration: Reconnect the upper PROFIBUS. The original IM 153-2 returns as standby. No further OB 86 events fire on the lower segment.
7. Failure test on lower segment: Disconnect one ET 200S from the lower PROFIBUS. The H-CPU logs OB 86 for that station; the Y-Link remains active. The other two ET 200S stations continue to run.
8. OS verification: In the PCS 7 OS, open the area picture for the Y-Link and verify that the redundancy status field shows Y-Link: redundant and that the three ET 200S stations show a green status.

Troubleshooting Matrix

Field-Proven Engineering Notes

• Use the diagnostic repeater (6ES7972-0AB01-0XA0) between the Y-Link active IM 153-2 and the lower segment. It isolates a cable break on one drop so that the other two ET 200S stations continue to run.
• Set the Y-Link monitoring time to at least 3× the configured PROFIBUS cycle on the upper segments. A 1.5 Mbps bus with one H station and one Y-Link on each side typically runs at 5–10 ms cycle; 100 ms is a comfortable monitoring time.
• For failsafe ET 200S modules, use the F-variant IM 151-1 F (PROFIsafe over PROFIBUS). The PROFINET/PROFIsafe address must be assigned in HW Config and cannot be changed at the device. PROFIsafe over the Y-Link is supported but adds ~30 ms to the fail-safe time; verify against the SIL calculation.
• When migrating a Y-Link configuration to a newer PCS 7 version, recompile the H station first. Do not mix compiled HW Config from a previous version with a current PCS 7 OS — diagnostic block version mismatches surface as transient OB 85 events.
• Always name the Y-Link in HW Config (right-click > Object Properties > Comment) with its physical location, e.g. Y-LINK_MARSHALLING_CABINET_A1. This name appears in the diagnostic buffer and on the OS, which is essential for fast field troubleshooting.

References to Official Documentation

For deeper reading, the following official Siemens documents apply:

• Siemens Support entry 43688632 – How is the Y-Link structured? — primary reference for Y-Link architecture and 255-byte limit.
• SIMATIC ET 200M Signal Modules / Interface Module IM 153-2 manual (Siemens Support, search 6ES7153-2BA10).
• SIMATIC ET 200S Distributed I/O System manual (Siemens Support, search 6ES7151-1Axx).
• SIMATIC PCS 7 Process Control System Engineering manual (current version on Siemens Support).
• PROFIBUS standard IEC 61158 / IEC 61784 for DP-V0 / DP-V1 / DP-V2 service definitions referenced by the Y-Link.