Problem Overview
On PCS 7 V8.2 (non-SP1) plants built around a redundant SIMATIC S7-410-5H automation station with firmware V8.2.2, performing an online Connections and Gateways download from NetPro (SIMATIC Manager / STEP 7 V5.5 SPx) drops every Ethernet connection that traverses the CP 443-1 communications processor for approximately 5–10 seconds. OS servers using ISO transport, plus remote S7 connections and Modbus TCP slaves addressed over IP, all report a simultaneous outage while the download is committed. Communications self-recover once the download finishes; no manual intervention is required. The behavior has been observed to be deterministic (3 of 3 attempts produced the same fault).
The CPU diagnostic buffer remains empty during the event. Only the CP 443-1 diagnostic buffer records the disruption, producing three repeating entries that correspond to teardown and re-establishment of the module's internal system connection to the CPU backplane. Because the plant bus is entirely concentrated on the CP — no devices are attached to the CPU's integrated PROFINET/IE port — every AS-OS link, every remote S7 put/get, and every Modbus TCP exchange is impacted at once.
Affected System Configuration
The reference configuration that triggers the fault is summarized below. Any field installation matching more than two of these criteria is likely to reproduce the symptom.
| Parameter | Value |
|---|---|
| PCS 7 version | V8.2 (no Service Pack applied) |
| SIMATIC Manager / STEP 7 | V5.5 + SP4/K5.5.0.x (PCS 7 V8.2 baseline) |
| AS hardware | 6ES7 410-5H08-0AB0 (CPU 410-5H, firmware V8.2.2) |
| CP module | 1 × 6GK7 443-1EX30-0XE0 (CP 443-1) per AS rack, in slot configured for plant bus |
| Plant-bus topology | All Ethernet devices (OS servers, S7 partners, Modbus TCP slaves) terminated on the CP 443-1, none on CPU PN/IE port |
| OS-AS transport | ISO-on-TCP (RFC 1006) via the CP |
| Remote S7 partner count | 5 configured S7 connections |
| Modbus TCP partner count | 9 configured TCP connections (CP acting as Modbus server or as gateway) |
| Data volume per connection | 10–20 registers / 10–20 bytes payload each |
Symptom Analysis — CP 443-1 Event ID Decoding
Three diagnostic events appear in sequence inside the CP 443-1 information log during the 5–10 second outage. The IDs map to the CP 443-1 internal status/state machine described in the Siemens SIMATIC NET CP 443-1 manual (entry ID 59185238 in the Siemens Industry Online Support).
| Event ID (hex) | Plain-language meaning | Category | Direction |
|---|---|---|---|
| 16#F9C1-261D | System connection from CP to CPU was terminated actively by the module (internal info 1 = external error, incoming event) | Status / Link | Incoming (reported by CP) |
| 16#F9C1-2615 | System connection between CP and CPU was closed (external error, incoming event) | Status / Link | Incoming (reported by CP) |
| 16#F9C1-2614 | System connection between CP and CPU was established (external error, incoming event) | Status / Link | Incoming (reported by CP) |
The fact that the CP, not the CPU, logs the event is itself diagnostic: it tells you that the CP released its backplane channel first. When a CPU-initiated STOP/RUN transition causes the same symptom, the CPU diagnostic buffer (not the CP buffer) carries the corresponding entry. An empty CPU buffer combined with the trio above isolates the cause to CP-side restart of the system channel — exactly what happens when CP configuration data is overwritten by a NetPro download.
Root Cause Analysis
The NetPro Connections and Gateways download pushes the entire S7 connection table to the CPU. The CPU then re-distributes the relevant slices of that table to every CP whose configuration depends on it. On CP 443-1 firmware versions shipped with PCS 7 V8.2 (firmware V3.x of the EX30 module), receiving a new connection table forces the CP to:
- Close every active ISO and TCP socket the CP holds on behalf of plant-bus partners.
- Tear down its internal backplane channel to the CPU (event F9C1-261D).
- Reload its connection block from the CPU (event F9C1-2615).
- Re-open the backplane channel (event F9C1-2614).
- Re-establish each external socket against the new connection table.
Steps 1 through 4 are unavoidable on the EX30 at firmware V3.x; the runtime reserves no "delta" mode that would allow hot patching of individual connections. This is consistent with the wording used in Siemens PCS 7 V8.2 — Service & Commissioning documentation that warns of short plant-bus interruptions during a connection download only when all plant-bus traffic is concentrated on a single CP and the connections in question are downloaded in a single NetPro transaction.
Three architectural factors amplify the symptom:
- Single CP per rack: with one CP 443-1 carrying the entire plant bus, there is no redundant path that could absorb the interruption.
- No CPU PN/IE traffic: nothing is connected to the integrated Ethernet port of the 410-5H, so there is no independent subnet to survive the CP restart.
- Mixed ISO + IP partners: ISO transport re-handshakes faster than IP sockets, which is why the OS gray screen clears within seconds while Modbus TCP partners may show longer recovery times on partners that don't aggressively retry.
Architecture Considerations — CPU PN/IE vs CP 443-1
The CPU 410-5H integrates two PROFINET interfaces (X1, X2) that are full members of the AS backplane and can carry S7 connections, ISO-on-TCP, TCP, and PROFINET IO independently of any CP. Using the integrated port for some classes of traffic is the standard Siemens recommendation for PCS 7 V8.2 plants where bumpless connection edits matter. The table below shows the recommended assignment.
| Traffic class | Recommended interface | Reason |
|---|---|---|
| OS-AS (WinCC redundancy) | CPU 410-5H PN/IE (X1) or CP 443-1, but not both in the same AS | OS license and PCS 7 standard AS-OS coupling assume a single, deterministic path |
| Remote S7 put/get (cross-plant, partner PLCs) | CPU PN/IE (X1) preferred | Survives CP 443-1 download events |
| Modbus TCP gateway / Modbus pool | CP 443-1 (EX30) preferred | CP 443-1 holds the Modbus/TCP license stamp; routing via PN requires the Modbus TCP PN-CPU option |
| PROFINET IO to ET 200M / ET 200SP | CPU PN/IE (X1 or X2, separate subnet) | PROFINET IO controller is the CPU; CP 443-1 does not support PROFINET IO |
| Field-level HMI panels | CP 443-1 or PN, per panel count | CPU PN has stricter connection limits per port |
If you must keep all traffic on a single CP, see Workarounds and Mitigations below.
Workarounds and Mitigations
Apply mitigations in the order listed; each one is independently sufficient for many sites, and stacking them gives the strongest guarantee.
Workaround 1 — Split traffic across CPU PN/IE and CP 443-1
- In HW Config, configure the CPU 410-5H PROFINET interface X1 with an IP address on a dedicated subnet (for example 192.168.10.0/24) reserved for the OS pair.
- Configure the CP 443-1 on a separate subnet (for example 192.168.20.0/24) used by remote S7 and Modbus TCP.
- Recreate the OS connections to point at the CPU PN IP rather than the CP IP.
- Recreate the S7 put/get partner connections to point at the CPU PN IP.
- Leave Modbus TCP on the CP (CP holds the Modbus TCP license stamp).
- Download Connections and Gateways. Only the Modbus TCP partners on the CP will experience the 5–10 second outage; OS and remote S7 connections stay up.
Workaround 2 — Apply CP 443-1 firmware update
Newer CP 443-1 EX30 firmware (V3.2.7 and later, depending on the order number suffix) improved the hot-reload behavior of the connection table. Confirm the article ID with Siemens Industry Online Support; the entry is referenced in the CP 443-1 Firmware V3.2 release notes (search entry ID 109750304). Upgrading the CP firmware requires:
- Download the new firmware from Siemens Industry Online Support (entry ID listed in your hardware's manual under "Firmware").
- Use SIMATIC Manager > Options > Install Firmware to flash the CP.
- Perform the upgrade during a planned maintenance window — the CP will reboot and disconnect for up to 60 seconds.
- Re-test the connection download; the 5–10 second outage typically shortens to <2 s, or disappears entirely for ISO-only partners.
Workaround 3 — Apply PCS 7 V8.2 SP1 or later
PCS 7 V8.2 SP1 (and the cumulative update packages that followed) contained several corrections to NetPro download behavior on H-CPUs and to CP 443-1 re-initialization timing. Where the operating environment permits, upgrade the engineering station and the AS to PCS 7 V8.2 SP2 or later. See Siemens entry ID 109751604 for the V8.2 SP2 readme and entry ID 109769245 for the SP3 readme.
Workaround 4 — Sequential, partner-by-partner connection download
If architecture changes are forbidden and firmware upgrades are blocked, perform the connection download one connection at a time. Each individual connection download still triggers a CP reload, but the gap between teardown and re-establishment is shorter (typically 1–2 s), and the OS retry logic absorbs the brief outage without generating an alarm storm.
- In NetPro, select a single connection.
- Right-click > Download to Target System > Connections and Gateways.
- Wait 30 seconds for the OS partner to confirm re-establishment.
- Repeat for the next connection.
Workaround 5 — Suppress OS alarm storm during the window
Even when the underlying outage cannot be eliminated, you can prevent the OS from paging on every connection loss:
- In WinCC Explorer > Computer properties > Startup, increase the connection monitoring timeout.
- On the OS server, raise the OPC / channel retry interval for the S7 channel to 5 seconds.
- Enable the "Suppress connection-loss messages" bit in the AS-OS alarm mask (in CFC, the @PCS7_OS_ALARM block parameter
Suppress).
This does not fix the underlying outage — it only prevents it from being observable. Use it only as a temporary measure.
Step-by-Step: Reproducing the Fault in a Lab Setting
- Build a 410-5H rack with one CP 443-1 EX30 and one OS server on the plant bus.
- Configure 5 S7 connections and 9 Modbus TCP connections, mirroring the production connection count.
- Confirm all OS partner connections are in "established" state (check the WinCC channel diagnostics).
- Open NetPro, select PLC > Download to Target System > Connections and Gateways.
- Target the rack 0 CPU.
- Watch the CP 443-1 information log in SIMATIC Manager > PLC > Diagnose Hardware; expect the F9C1-261D/2615/2614 triplet within 1 second of download start.
- Observe the WinCC channel status; expect "disconnected" for ~5–10 s, then automatic recovery.
Verification and Monitoring
After applying any mitigation, verify the outcome using the following checks:
| Check | Method | Pass criterion |
|---|---|---|
| OS-AS link | WinCC channel diagnosis > S7 channel status | No "disconnected" transitions during download |
| Remote S7 put/get | Partner PLC diagnostic buffer / partner CP log | No F9C1 / FC11 disconnect events during download |
| Modbus TCP | Wireshark capture on plant-bus switch port | No FIN/ACK on Modbus sockets during the download window |
| CP 443-1 info log | SIMATIC Manager > PLC > Diagnose Hardware > Information Log | No F9C1-261D entries during the download |
| CPU 410-5H diagnostic buffer | SIMATIC Manager > PLC > Diagnose Hardware > Diagnostic Buffer | No STOP/RUN transitions, no mode changes |
| WinCC alarm log | Alarm logging archive | Zero "connection failure" alarms during the download window |
Troubleshooting Matrix
| Symptom | Likely cause | First action |
|---|---|---|
| OS goes gray for 5–10 s during connection download | CP 443-1 system-connection reset (this article) | Confirm F9C1-261D/2615/2614 in CP log; apply Workaround 1 (split to CPU PN) |
| OS goes gray AND CPU STOP/RUN transition appears in CPU diagnostic buffer | CPU STOP triggered by download | Verify the download target is the AS-OS connection block, not the S7 program; do not download the entire station |
| Intermittent gray screens unrelated to downloads | Plant-bus network issue | Check switch port counters, CRC errors, duplex mismatch |
| CP diagnostic buffer repeatedly shows F9C1-261D even without downloads | CP backplane connector / firmware fault | Reseat the CP; if persistent, replace CP and escalate to Siemens support with the CP serial number and firmware version |
| OS gray screens only on the standby OS server | OS redundancy configuration mismatch | Re-check WinCC redundancy partner settings, not the CP |
Firmware and Release Notes Reference
Always confirm the firmware and software versions in scope against the live Siemens Industry Online Support portal before upgrading:
- CPU 410-5H firmware V8.2.2: baseline release for PCS 7 V8.2; later 410-5H firmware bundles (V8.2.3, V8.2.4, V9.0) progressively improved the CP backplane handshake.
- CP 443-1 (6GK7 443-1EX30-0XE0): firmware V3.0.x ships with PCS 7 V8.2; firmware V3.2.x and later reduce the connection-table reload interruption. Verify against the order-number-specific release notes on the Siemens support portal.
- STEP 7 / SIMATIC Manager V5.5 SPx: NetPro download logic is also affected by the SP level. Apply the latest K5.5.x.x hotfix bundle available for your installed baseline.
- PCS 7 V8.2 SP1 / SP2 / SP3: service packs bundle the CP firmware and STEP 7 hotfixes; upgrading to SP2 is the cleanest single-step mitigation when an architectural change is not possible.
For an order-number-specific firmware search, use the Siemens Industry Online Support product tree for the relevant module; the firmware download is gated behind a Siemens registration login.
FAQ
What does CP 443-1 event ID 16#F9C1-261D mean?
It means the CP 443-1 actively closed its internal system connection to the CPU backplane. In a Connections and Gateways download it is the first in a triplet (261D → 2615 → 2614) that documents the teardown, reload, and re-establishment of the CP's configuration channel. The CPU diagnostic buffer remains empty because the CPU is not the initiator of the disconnect.
Can a Connections and Gateways download be bumpless when all plant-bus traffic is on a single CP 443-1?
No. On CP 443-1 firmware versions shipped with PCS 7 V8.2 (no SP), every connection-table download forces a CP reload that closes all external sockets for approximately 5–10 seconds. To make the download bumpless for at least some traffic, split the OS-AS and remote S7 connections to the CPU 410-5H PROFINET port and keep only Modbus TCP on the CP.
How many S7 connections can a CP 443-1 hold?
CP 443-1 EX30 supports up to 64 S7 connections in total, including OS, S7 put/get, and Modbus TCP connections. 5 S7 + 9 Modbus TCP + 2 redundant OS connections is well under the limit, so the interruption is not caused by connection-count saturation; it is caused by the CP-wide reload during download.
Does upgrading to PCS 7 V8.2 SP1 or later fix the issue?
Usually, yes. SP1 and later bundles corrected the CP 443-1 reload timing for connection-table downloads, and the CP firmware shipped with the SPs further reduced the reload window. Confirm the SP readme for the exact list of CP-related corrections.
Is there a way to download only one connection without bumping the others?
On PCS 7 V8.2 with the CP 443-1 EX30 firmware V3.0.x, no — the CP reloads its entire connection table on every download, even for a single connection. Workaround 4 (sequential partner-by-partner downloads) reduces the visibility of the bump by keeping the reload window to 1–2 s instead of 5–10 s, but it does not eliminate it.