S7-400H PROFINET on CPU 414-5H vs CP443-1: When Each Interface Is Required

The recurring engineering question on the S7-400H platform is straightforward: if the redundant CPU pair already carries an integrated PROFINET interface, do the two CP 443-1 communication processors still have to be configured, ordered, and installed? The answer is conditional. For most non-safety, non-routed HMI/PG, and standard PROFINET I/O tasks the integrated PROFINET port of the CPU 414-5H PN/DP (order number 6ES7414-5HM06-0AB0) is functionally sufficient, but several production-grade scenarios in redundant H-systems still require one or two CP 443-1 modules per CPU. This reference walks through the architecture, the catalog capabilities, the redundancy topology with the IM 155-5 PN HF (6ES7155-5AA00-0AC0), and a field-ready decision matrix.

1. S7-400H System Architecture Recap

The S7-400H is Siemens' high-availability PLC platform designed for fail-safe, hot-standby operation. Two CPUs of identical type and firmware execute identical user programs and synchronize via fiber-optic sync modules (up to 10 km with the appropriate sync module). A fault on the master causes the reserve to take over bumplessly. Communication is duplicated to match the redundancy model:

• Two independent PROFINET networks, each terminating on one of the H-CPUs (or a CP).
• Two independent PROFIBUS DP networks, each terminating on the integrated DP master of the CPU or on a CP 443-5 Extended.
• Two sync-module links (fiber pair) for event-synchronous data exchange between the two halves.

Communication processors are not "nice to have"; they are part of the redundant channel plan. A single CP 443-1 on one CPU creates an asymmetric failure domain: if that CPU fails, the CP goes with it. For S7-400H the rule is that any external network required for the process must be reachable from both halves of the pair.

2. CPU 414-5H PN/DP (6ES7414-5HM06-0AB0) Integrated Interfaces

The 6ES7414-5HM06-0AB0 is the PROFINET-enabled variant of the CPU 414-5H. Its on-board interface set is the starting point of the decision:

The integrated PROFINET is a managed 2-port switch (100 Mbit/s, full duplex, auto-negotiation, auto-crossover). It supports PROFINET IO controller, IO device (I-device), and the full TCP/IP stack for S7 communication, open user communication (T-blocks), ISO-on-TCP, TCP, UDP, and the integrated web server. The number of PROFINET IO devices, S7 connections, and HMI connections is finite and CPU-specific. The CPU 414-5H PN/DP supports the lower tier of connection resources of the H family, so on dense HMI or routing projects the integrated port can saturate quickly.

3. CP 443-1 Family and Where It Is Used

CP 443-1 is the external PROFINET/Industrial Ethernet communication processor for the S7-400 and S7-400H. Variants relevant to H-systems include:

The CP 443-1 occupies one slot in the S7-400 rack and is configured in STEP 7 V5.x (and in TIA Portal for compatible variants) as a separate PROFINET IO system. It brings its own set of connection resources independent of the CPU. In S7-400H each rack hosts one CP 443-1 per CPU, and the two CPs are configured as a redundant pair using the H-system redundancy mechanism in HW Config (H-station editor).

4. Functional Comparison: Integrated PROFINET vs. CP 443-1

The following table captures the engineering-relevant differences for the S7-400H use case. "Both" indicates equivalent support on the integrated port of the CPU 414-5H PN/DP and on the CP 443-1.

The two columns are functionally similar for the standard PROFINET IO controller role. The differences become decisive for connection-resource isolation, gigabit uplinks, OPC UA, IP routing, Modbus TCP, and for separating the HMI/PG traffic from the IO traffic on a redundant network.

5. System Redundancy and the IM 155-5 PN HF

In the S7-400H the PROFINET IO field is normally built from two independent PN networks (PN1 and PN2), each connecting to a redundant IO station. The standard interface module on those stations is the IM 155-5 PN HF (6ES7155-5AA00-0AC0). The Siemens TIA Portal documentation explicitly states that when system redundancy is used, the IM 155-5 PN HF can be connected to H-CPUs with system redundancy, allowing a single IO station to be reachable from both H-CPUs simultaneously and to survive the loss of one H-CPU without reconfiguration.

From a topology perspective, two valid constructions exist:

5.1 Topology A - Integrated PROFINET only

Each H-CPU connects to one of the two PN rings. The two IM 155-5 PN HF stations of the redundant IO line are physically split: one IM is on PN1 (the integrated port of CPU A), the partner IM is on PN2 (the integrated port of CPU B). The ET 200MP station then internally couples the two IM 155-5 PN HF backplanes via the backplane bus, so the same I/O modules are visible to both H-CPUs.

This topology is valid, is documented in the IM 155-5 PN HF system-redundancy section of the ET 200MP manual, and it does not require any CP 443-1.

5.2 Topology B - Integrated PROFINET plus CP 443-1

The integrated PROFINET is dedicated to PROFINET IO (the field network). A CP 443-1 per CPU is added for HMI, PG, and external routed traffic on a separate plant network. The two CPs are configured as a redundant pair in the H-station editor; the partner CP takes over seamlessly if the active CP fails.

The redundancy model is identical: each network has two physical paths, one from each half of the H-pair. The difference is functional separation - IO traffic on the integrated ports, HMI/PG on the CPs - which is the most common production-grade pattern in S7-400H plants.

6. When the CP 443-1 Is Required

Despite the integrated PROFINET port, the following conditions make a CP 443-1 per CPU mandatory, or at least strongly recommended, in S7-400H:

1. HMI/PG resource isolation. Every S7 connection, every HMI variable, and every PG routing slot consumes a connection resource. On dense HMI deployments (50+ WinCC tags/second, multiple Comfort Panels, WinCC Runtime) the CPU 414-5H connection budget can be exhausted before the IO budget is reached. Moving HMI traffic to a CP 443-1 leaves the CPU resources for IO and program execution.
2. OPC UA exposure. The CPU integrated port does not run an OPC UA server in the S7-400H generation. If an OPC UA client (SCADA, MES, third-party historian) must read the PLC, a CP 443-1 OPC UA (6GK7443-1UX00-0XE0) is the only in-rack solution.
3. Modbus TCP master/slave. The integrated port has no certified Modbus/TCP server stack. CP 443-1 with Modbus/TCP option supports polled and unsolicited Modbus communication with up to 64 connections per CP.
4. IP routing with Access Control List. When the H-system is the gateway between the field network and the control network, the CP 443-1 (firmware V3.x and later) provides a routable interface with ACL and time-stamped diagnostics. The CPU integrated port can route but lacks the granular ACL.
5. Gigabit uplink to the control network. The integrated port is 100 Mbit/s. If the plant network is gigabit (typical for video, large WinCC, or remote IO), the CP 443-1 EX40 (6GK7443-1EX40-0XE0) brings the gigabit uplink.
6. Logical network separation for cybersecurity. Many plant-architecture standards (IEC 62443, ISA 99 zones and conduits) require that the HMI/SCADA network be on a separate routed segment from the IO network. A CP 443-1 is the conduit; the integrated port is the field network.
7. Connection-redundancy for non-PROFINET-PROFINET paths. Although system redundancy is handled between the integrated ports and the IM 155-5 PN HF, S7-classic connections and open IE connections to a third-party system benefit from a redundant CP pair so that a single CP failure does not break the link.

7. When the CP 443-1 Is Not Required

Conversely, the following conditions allow the integrated PROFINET of the 6ES7414-5HM06-0AB0 to carry the full communication load, and the two CP 443-1 modules can be omitted from the bill of materials:

1. The PROFINET IO field is the only network needed (no HMI, no SCADA uplink, no PG from outside the rack).
2. PG access is local to the rack or to a single PN network segment.
3. HMI is implemented as PROFINET IO panels (Comfort Panels with PN connection to the IO network), not as S7-communication clients on a separate network.
4. Connection count remains inside the CPU 414-5H resource budget (verify with STEP 7 Connection Diagnostics: the warning threshold is 80% of the budget).
5. No OPC UA, no Modbus TCP, no IP routing, no gigabit uplink required.
6. The system-redundancy pattern with IM 155-5 PN HF (6ES7155-5AA00-0AC0) is implemented and the IO stations support S2 redundancy.

In these constrained greenfield configurations the cost saving is two CP 443-1 modules (roughly EUR 1,500 - 3,000 each, plus a slot in each rack and a SIMATIC NET manual) and the engineering effort to commission the redundant CP pair.

8. Decision Matrix

9. Configuration Steps in STEP 7 V5.x for Topology A (Integrated PROFINET only)

1. Open SIMATIC Manager and load the H-station from the offline archive of the 414-5H pair.
2. In HW Config, click on the H-CPU and open the PROFINET interface "PN-IO" properties. Assign an IP address and a PROFINET device name to each CPU (two independent IP subnets, e.g. 192.168.1.1 for CPU A and 192.168.2.1 for CPU B).
3. Insert an ET 200MP station. In its slot 0, place the IM 155-5 PN HF (6ES7155-5AA00-0AC0). Assign it a device name in the same subnet as CPU A.
4. Place a second IM 155-5 PN HF in the same ET 200MP station, on the backplane. Assign it the device name in CPU B's subnet. The two IMs together form the S2-redundancy-capable interface to the H-system.
5. Configure the IO modules on the backplane. They are visible to both H-CPUs through the system-redundancy mechanism.
6. Set the redundancy role of the H-CPUs (master/reserve) in the H-station editor. The CPU with the lower rack number is normally the master.
7. Compile and download. Verify in NetPro that the H-system redundancy is consistent (both CPU PROFINET interfaces show the same PN IO system number, two independent subnet rows).

10. Configuration Steps for Topology B (Integrated PN + CP 443-1 Pair)

1. Same as Topology A, steps 1-2, for the integrated PROFINET (field network).
2. In the rack, insert a CP 443-1 (e.g. 6GK7443-1EX30-0XE0) into a free slot of each H-CPU rack. Each CP gets its own IP address in the plant network (e.g. 192.168.10.2 for CP-A, 192.168.10.3 for CP-B).
3. Open the CP 443-1 properties and, in the "H-system redundancy" tab, mark both CPs as part of the H-redundant pair. STEP 7 will automatically configure the H-sync for the CP pair.
4. Create the S7 connections from the WinCC server or HMI panels to the redundant CP pair. The HMI uses the MAC address of the active CP for ISO-on-TCP or the virtual IP of the redundant CP pair (defined in the CP properties).
5. For OPC UA, select the CP 443-1 OPC UA (6GK7443-1UX00-0XE0) variant and enable the OPC UA server in the CP properties. Configure the security policy and the authentication certificate.
6. For IP routing, enable the router function in the CP properties and add the static routes. The CP then becomes the default gateway for the H-station into the plant network.
7. Compile, download, and run a connection test from WinCC to the virtual IP. Verify with the CP web server that the active CP is the expected one.

11. Verification Checklist

After commissioning either topology, perform the following verification steps:

• PROFINET IO startup. All IO stations reach the active CPU within the configured PROFINET startup time (typically 1-3 s). The partner IM 155-5 PN HF should report "standby" in the device diagnostics.
• CPU switchover test. Stop the active CPU via the H-station control panel. The reserve CPU must take over within <100 ms, IO must continue updating, HMI must not lose the S7 connection.
• CP switchover test (Topology B). Disconnect the network cable from the active CP 443-1. The partner CP must take over the plant-network connection within 1-3 s. Verify with WinCC: no "connection broken" alarm.
• Connection-resource check. Open the CPU diagnostics buffer and the CP diagnostics web page. Confirm that the number of active connections is below 80% of the configured maximum.
• Sync link health. In the H-station diagnostics, both fiber sync links must be GREEN. Any YELLOW or RED state disqualifies redundancy and must be cleared before production run.

12. Field-Proven Caveats and Edge Cases

13. Common Misconceptions

"PROFINET means all PROFINET features are present." False for the S7-400H generation. The integrated port of the CPU 414-5H PN/DP does not provide an OPC UA server, a certified Modbus/TCP stack, or gigabit. Those features live on the CP family.

"Two CPs in H-rack means double the bandwidth." False. The H-redundant CP pair shares the same logical plant network and the active CP is the single point of contact. The partner CP is a standby, not a load-balancer.

"IM 155-5 PN HF works the same in PROFINET and in S7-400H system-redundancy mode." Functionally the same module, but the configuration of the redundancy role differs. The system-redundancy configuration path is described in the Siemens TIA Portal ET 200MP manual collection, system redundancy on S7-400H section.

14. Cost and Engineering Trade-Off Summary

15. Recommendation

For a greenfield S7-400H with the CPU 414-5H PN/DP (6ES7414-5HM06-0AB0), start the design with the integrated PROFINET for the PROFINET IO field and the IM 155-5 PN HF for the redundant IO stations. Add the CP 443-1 pair as soon as any of the following is true: more than 10 HMI clients, an OPC UA requirement, a Modbus TCP requirement, a gigabit plant network, or a cybersecurity mandate for routed network separation. The CP 443-1 is not redundant in the sense of load-sharing; it is redundant in the sense that the plant network remains reachable when either half of the H-pair is unavailable.

For brownfield migrations, retain the existing CP 443-1 pair and consider it part of the H-system's external contract with the HMI/SCADA. Do not remove the CP 443-1 from an existing project without a planned outage and a full re-pointing of every HMI connection.