S7-1200 and KTP900 IP Address Reconfiguration Field Guide

Overview

Replacing the IP addresses of a deployed Siemens SIMATIC S7-1200 CPU (for example, a CPU 1215C such as 6ES7215-1AG40-0XB0) and a KTP900 HMI panel without the original TIA Portal project is a routine field task. It occurs whenever a working machine is migrated into a wider industrial network, the original integrator is no longer available, or the engineer on-site only has the compiled runtime on the HMI and not the source project. The challenge is two-fold: the IP of the PLC must be reassigned, and the connection that the HMI uses to reach the PLC (stored inside the compiled HMI project) must be redirected to the new PLC IP.

This guide consolidates the four practical methods used in the field:

1. Service and Commissioning menu on the KTP panel (firmware 13.0.1 or later).
2. PRONETA network tool from Siemens.
3. T_CONFIG instruction inside the S7-1200 user program.
4. SIMATIC Automation Tool for batch IP changes across many stations.

The methods are complementary; the correct choice depends on the firmware version, whether the original TIA Portal project is available, and whether the engineer is present physically at the cabinet or working remotely over a VPN link.

Prerequisites

Method 1 - Service and Commissioning Menu on the KTP900

This is the only method that allows both the panel IP and the connection target (PLC IP) to be changed directly from the panel touch screen, without the original TIA Portal project and without uploading any project from the HMI. It was introduced on the second-generation Basic Panels (KTP400, KTP700, KTP900, KTP1200) at firmware V13.0.1 and is the path the original poster ultimately used.

Step 1 - Change the PLC IP first

Before touching the HMI, change the PLC IP. The PLC must be reachable during the next step when the HMI is told where to find it. Either use:

• TIA Portal: Online > Accessible nodes > select CPU > Online & Diagnostics > Functions > Assign IP address.
• PRONETA: see Method 2.
• T_CONFIG: see Method 3.

Confirm the new IP responds to a ping from the engineering station before continuing.

Step 2 - Power-cycle both devices

De-energize the S7-1200 and the KTP900 simultaneously and power them back on. The Service menu on the panel only appears during the boot sequence; once the runtime is up, the touch screen is fully occupied by the project.

Step 3 - Reach the Settings tab

On the KTP900 splash screen, the "Settings" button is visible only for a short window after power-up. Tap it before the runtime starts. Navigate:

1. Settings > Service and Commissioning.
2. Tap the "Edit connections" tab in the lower-left corner.

On older firmware, only the loader appears. In that case, fall back to Method 2 or restore the panel image with a known-good backup before proceeding.

Step 4 - Override and re-point the connection

The wizard shows the configured HMI connection(s). The three-step wizard is:

1. Select the connection (HMI connection to the S7-1200).
2. Set "Override" to ON. This forces the new value into the runtime configuration.
3. Enter the new PLC IP, confirm subnet, and write to the panel.

Step 5 - Change the panel IP itself

From the same Service and Commissioning screen, change the KTP900's own IP address. With Override still active, write the change to flash. The panel reboots automatically with the new IP and the new PLC target.

Step 6 - Verification

After the panel returns to the project, the first screen should populate with live tags. If the data fields stay at "####" or "0", the connection has not been redirected correctly. Re-enter the wizard and re-check the Override state and the entered IP.

Method 2 - PRONETA Tool

PRONETA (PROFINET Network Analysis) is a free Windows utility from Siemens used to scan, analyze, and configure PROFINET networks. It is the recommended tool for any engineer who does not have the original project because it shows the live topology and the live IP of every device, including devices whose project configuration has been lost.

The official entry point and application example are documented at the Siemens Industry Online Support entry Application example 67460624 - Network analysis with PRONETA.

Procedure

1. Install PRONETA on the engineering station. Set the PG/PC Ethernet adapter to the same subnet as the existing PLC IP.
2. Start a network scan. PRONETA uses DCP (Discovery and Configuration Protocol) and lists every PROFINET device that responds, including its current IP, MAC, device name, and type.
3. Right-click the S7-1200 CPU and select "Edit network parameters". Enter the new IP and subnet mask, click Save. The change is written to the CPU immediately.
4. Right-click the KTP900 and assign its new IP the same way.

PRONETA also supports the IO Test function (against the CPU), flashing of LED identification, assignment of PROFINET device names, and topology discovery with port-to-port cable tracing on managed switches.

Method 3 - T_CONFIG Instruction in the S7-1200 User Program

The T_CONFIG instruction is a Siemens library block used inside the S7-1200 user program to write IP, subnet, PROFINET device name, and routing parameters to a PROFINET interface at runtime. It is appropriate when the PLC is the master in a redundant network or when the IP must change as part of an application workflow (for example, two identical machines that swap roles and need different IPs on a rotating schedule).

The TIA Portal reference for the instruction is in the SIMATIC S7-1200 Programmable Controller System Manual, communication section: Example - Using the T_CONFIG instruction to change IP parameters.

Hardware configuration prerequisite

In the CPU's Properties dialog under "Ethernet address", the IP assignment must be set to "IP address is set directly at the device". If the project still has "IP address is set in the project", the configuration download will overwrite any value T_CONFIG writes at runtime.

Block call (SCL example)

// T_CONFIG: change PROFINET interface IP at runtime
// Instance: "T_CONFIG_DB"
// IFACE_ID = local PROFINET interface (X1 = 0, X2 = 1 on CPUs that expose two ports)

"T_CONFIG_DB"(REQ   := StartChange,          // edge-triggered start
             IFACE := "Local PROFINET interface_1",
             CONF  := "TADDR_Conf",           // VARIANT pointing at a configured DATA block
             DONE  => DoneFlag,
             BUSY  => BusyFlag,
             ERROR => ErrorFlag,
             STATUS => StatusWord);

// TADDR_Conf describes interface ID, IP, subnet, gateway, name.
// See the TIA Portal help page for the exact UDT layout.

After a successful T_CONFIG write, the CPU resets the PROFINET interface and the new IP becomes active on the next connection. Plan a short pause (typically 3 to 10 seconds) in the application before the HMI attempts to reconnect.

Method 4 - SIMATIC Automation Tool

For larger plants with many S7-1200 / S7-1500 / ET 200 stations, the SIMATIC Automation Tool (SAT) replaces PRONETA. SAT can scan, change IP, change PROFINET name, set PG/PC routing, run firmware updates, and copy programs in batch from a single CSV-driven job. The installer is hosted on the Siemens Industry Online Support portal under entry 98161626 (SIMATIC Automation Tool).

SAT, like PRONETA, only updates the IP of the devices themselves. The HMI-side redirection is still the responsibility of the panel wizard or a TIA Portal project edit.

Choosing the Right Method

Recommended Procedure for the Common Migration Case

The migration case in the field report was:

• PLC: 192.168.0.2 -> 192.168.0.22
• HMI: 192.168.0.3 -> 192.168.0.23

1. Set PG/PC to 192.168.0.100 / 255.255.255.0 and verify ping to 192.168.0.2 and 192.168.0.3.
2. Run PRONETA, confirm both devices are visible and capture their MAC addresses for documentation.
3. Change PLC IP to 192.168.0.22 via PRONETA or TIA Portal. Ping the new IP. Confirm the old IP no longer responds.
4. Power-cycle both devices. On the KTP900, hit Settings during the boot splash, navigate to Service and Commissioning > Edit connections.
5. In the connection wizard, switch Override to ON, set the connection target IP to 192.168.0.22, write to the panel.
6. Change the panel IP to 192.168.0.23 in the same Service menu, write to flash.
7. Wait for the panel to reboot into the project. Verify that live tags populate within 30 seconds.
8. From the PG/PC at 192.168.0.100, ping both new IPs to confirm the network is reachable.
9. Document the change in the plant IP register.

Verification Checklist

Troubleshooting Matrix

Edge Cases and Field Caveats

Related Tools at a Glance

FAQ