Adding PROFINET to S7-300 CPU 315-2 DP via CP 343-1

Overview

The Siemens S7-300 family does not include a CPU with an integrated PROFINET interface in the same way the S7-1200 and S7-1500 lines do. The CPU 315-2 DP (order number 6ES7 315-2AG10-0AB0) ships with one MPI/DP interface and one pure DP master/slave interface; PROFINET must be added through an external communication processor. The standard solution is the CP 343-1 family, mounted in the S7-300 rack next to the CPU, which provides a PROFINET interface plus S7 communication, S5-compatible communication, and (depending on variant) open communication over TCP/UDP.

This reference covers the engineering decisions and configuration steps required to attach an ET 200S PROFINET station (interface module IM 155-6 PN BA, order number 6ES7 155-6AR00-0AN0) to an existing S7-300 site and to exchange DBs with neighbouring S7-1200 controllers using S7 communication. It also documents the symbolic-addressing limitations of the S7-300 platform that often surprise engineers coming from S7-1200/1500 backgrounds.

S7-300 PROFINET Architecture

Three paths exist to bring PROFINET into an S7-300 station. The selection is driven by the required role (IO controller vs. IO device), the communication services (S7, OPC, S5-compatible, open TCP), and the available slot count in the rack.

For an existing site with the CPU 315-2 AG10 in the rack and an empty slot available, adding the CP 343-1 (EX30) is the lowest-risk path. The CPU swap path (PN/DP variant) is the cleaner long-term solution but requires reloading the program and re-doing the hardware configuration.

CP 343-1 Hardware Selection (6GK7 343-1EX30-0XE0)

The 6GK7 343-1EX30-0XE0 is the EX30 firmware generation of the standard CP 343-1. The key technical characteristics relevant to a PROFINET IO controller deployment:

• 2 × RJ45 port, integrated 2-port switch (line topology supported without external switch)
• PROFINET IO controller, max. 128 IO devices (check firmware release notes for actual limit per FW version)
• PROFINET IO device (the CP can also be assigned as a device to a higher-level PN controller)
• S7 communication: server + client, Put/Get for DB exchange with S7-1200/1500/300/400
• Open communication: TCP/UDP, ISO-on-TCP, ISO transport, fetch/write (S5-compat.)
• Web diagnostics on the EX30 generation (basic)
• Configuration storage on the module; project upload possible

Before ordering, verify the slot count and the backplane bus load. Each CP occupies one slot in the S7-300 rack and consumes backplane resources. The CP should be placed as close as practical to the CPU, with no other modules between them that are not strictly needed for the configuration.

ET 200S vs ET 200SP Interface Module

The source scenario specifies the ET 200S distributed I/O system with interface module 6ES7 155-6AR00-0AN0 (IM 155-6 PN BA). The BA suffix indicates the Base feature set, which is sufficient for standard PROFINET IO operation but lacks advanced diagnostics and isochronous real-time (IRT) support. The ET 200SP with IM 155-6 PN is the recommended modern replacement; it is smaller, supports more modules, and integrates with TIA Portal's IO tag concept the same way as on S7-1200/1500 systems.

Prerequisites

1. Free rack slot in the S7-300 subrack for the CP 343-1, adjacent to or near the CPU. The CP uses a single slot.
2. Power budget: verify that the 5 V backplane supply on the rack's PS module can deliver the additional current drawn by the CP. The CP 343-1 typically draws 1.0–1.5 A at 5 V; the PS 305/307 datasheet lists the per-slot allocation.
3. TIA Portal with the HSP (Hardware Support Package) for the CP 343-1 EX30 installed. In TIA Portal V17/V18 this is included; older versions require the GSD/GSDML import plus an HSP for the IO device.
4. PROFINET device GSD for the IM 155-6 PN BA installed in TIA Portal (HSP for ET 200S PROFINET, or GSDML import).
5. Network topology planned: IP address range, device names, subnet mask, gateway (if any).
6. S7-1200 firmware ≥ V4.x on the peer CPUs for S7 communication Put/Get compatibility.

TIA Portal Configuration Procedure

Step 1 – Add the CP 343-1 to the Device Configuration

1. Open the S7-300 station in TIA Portal.
2. In the Device View, drag the CP 343-1 (6GK7 343-1EX30-0XE0) from the hardware catalog onto an empty slot in the rack.
3. Open the CP's Properties > Ethernet addresses and assign the PROFINET interface IP address, subnet mask, and (if used) router address.
4. Under PROFINET interface > PROFINET IO, enable IO controller operation.

Step 2 – Assign the ET 200S PN as IO Device

1. In the Network View, drag the IM 155-6 PN BA from the catalog and connect it to the CP's PROFINET port.
2. Assign a unique PROFINET device name to the ET 200S (the name is what the controller uses for AR establishment; IP alone is not sufficient on PROFINET).
3. Assign a unique IP address to the ET 200S, typically in the same subnet as the CP.
4. Open the ET 200S Device View and slot in the required I/O modules (DI, DO, AI, AO). The IO addresses are assigned automatically by TIA; you can override them in the I/O addresses tab of each module.

Step 3 – Assign Device Name (Topology Commissioning)

Before the ET 200S can be reached by the controller, its PROFINET device name must be written to the device. This is the step most often missed when migrating from DP (where MAC/address was the identification) to PROFINET.

1. Right-click the CP 343-1 in the network view → Assign device name.
2. In the Assign PROFINET device name dialog, browse accessible stations. The ET 200S appears with its MAC address and the currently assigned name (factory default is empty).
3. Select the target station, choose the correct PROFINET device name from the project, and click Assign name.
4. Verify the LED pattern on the IM 155-6 PN BA: a steady green link LED and absence of the BF (bus fault) LED indicate successful name assignment and AR establishment.

Step 4 – Compile and Download

1. Right-click the S7-300 station → Compile > Hardware (rebuild all).
2. Resolve any compile warnings. The most common warning on first-time CP integration is an unassigned PROFINET device name or a duplicate IP address on the subnet.
3. Download the hardware configuration to the CPU.
4. Download the CP 343-1 configuration (in TIA, the CP is downloaded as part of the station download).

Symbolic Addressing on S7-300 – What Works, What Doesn't

This is the critical engineering caveat for engineers familiar with S7-1200/1500. On S7-1200 and S7-1500, every PROFINET IO module slotted into the device view automatically generates symbolic IO tags (IO tags) and corresponding entries in the System constants tab. These tags can be dragged into the program, FB/FC parameter lists, and HMI tag tables.

On an S7-300 station with the CPU's own I/O or with a CP 343-1 hosting PROFINET IO, this automatic symbolic generation does not produce a writable tag list in the same way:

• The IO tags tab on the ET 200S device view remains empty or read-only because the IO is on the CP's address space, not the CPU's native process image.
• The System constants tab is empty for the CP-hosted devices.
• Direct symbolic names (Symbol Table > I1.5) still work, but the project will not auto-generate them from the hardware tree.

Workaround 1 – Direct Absolute Addressing

Use the absolute address (I 1.5, QW 4, etc.) directly in the program. The CPU scans the CP-hosted IO as part of the process image update; Ladder, FBD, STL, and SCL all accept absolute addresses. The drawback is loss of symbolic readability in the program.

Workaround 2 – Manual Symbol Table Entries

Open PLC tags > Default tag table and manually add a tag for each IO address. For example:

Tag name:    Motor_Start
Address:      I 1.5
Data type:    Bool
Comment:      ET200S DI module 0, channel 5

These manual entries are functionally identical to the auto-generated IO tags on S7-1200/1500. They can be used in the program, in HMI tag connections (with WinCC / TIA HMI), and in trace recordings.

Workaround 3 – Use a CPU with Integrated PROFINET

If the project allows a CPU replacement, the CPU 315-2 PN/DP (6ES7 315-2EH14-0AB0) provides an integrated PROFINET interface. The PROFINET IO devices attach to the CPU's own address space and the IO tags tab functions as expected. Existing S7-300 programs are compatible.

Workaround 4 – Migrate to ET 200SP

The ET 200SP IO family, when used with a CP 343-1, is still subject to the same S7-300 symbolic-addressing limitation because the CP is the IO controller. The platform-level limitation, not the IO device family, is the determining factor. ET 200SP does, however, offer better diagnostic granularity and module-level replacement without rack power-down.

S7 Communication with S7-1200 Peer CPUs

The requirement in the source scenario is to exchange DBs between the S7-300 (with CP 343-1) and multiple S7-1200 CPUs that already have PROFINET. The protocol of choice is S7 communication using PUT / GET blocks, available in both the S7-300 library and the S7-1200 library.

Configuration on S7-300 (CP 343-1 side)

1. Open the CP 343-1 Properties > S7 communication and enable PUT/GET as a server. The CP acts as a server that the S7-1200 can read/write to via PUT/GET.
2. Note the connection resource count: the EX30 supports a defined number of S7 connections. Each active S7 connection to a peer S7-1200 consumes one resource.
3. Program the S7-300 side as either a client (using FB14 GET, FB15 PUT from the Standard Library) or as a pure server. For periodic DB synchronization from the S7-300 master to the S7-1200 slaves, the master/active side typically runs PUT on the S7-300.

Configuration on S7-1200 Side

1. In the S7-1200 CPU Properties > Communication > S7 communication, enable Permit access with PUT/GET from remote partner. This is the firewall setting that blocks unauthorized S7 partners; it is disabled by default on S7-1200 firmware V4.x.
2. Drag a PUT or GET instruction into the S7-1200 program and configure the partner IP (CP 343-1 Ethernet address) and the partner rack/slot (S7-300 rack/slot where the CP is mounted, typically rack 0, slot 4 for the first CP).

Diagnostic and Verification

After download and commissioning, run the following verification matrix:

Troubleshooting Matrix

Engineering Recommendation Summary

1. For a new S7-300 PROFINET deployment with limited budget: use the CP 343-1 Lean (6GK7 343-1CX10-0XE0) and the ET 200S IM 155-6 PN BA already specified.
2. For a deployment requiring more than ~8 S7 connections, OPC UA, or extended web diagnostics: use the standard CP 343-1 (6GK7 343-1EX30-0XE0).
3. For a deployment that should integrate cleanly with TIA Portal's symbolic IO concept: replace the CPU 315-2 DP with the CPU 315-2 PN/DP (6ES7 315-2EH14-0AB0) and connect the ET 200S directly to the integrated PROFINET interface.
4. For new projects on existing S7-300 hardware: use ET 200SP IO devices rather than ET 200S. The replacement-part availability and diagnostic depth are significantly better, even though the S7-300 symbolic addressing caveat remains.

Field-Proven Caveats

• Hot-swap: ET 200S modules are not hot-swappable; the station must be powered down or the affected module must be in a configured-but-failed state for replacement. ET 200SP modules do support hot-swap with the appropriate BaseUnit configuration.
• Update time: The CP 343-1 update time for PROFINET IO is firmware-dependent. The default of 1 ms is sufficient for most discrete I/O. For high-speed applications, evaluate IRT availability before committing to the BA variant of the IM 155-6.
• Replacement part cycle: The IM 155-6 PN BA (6ES7 155-6AR00-0AN0) is being phased out in favor of the -6AU01 / -6AU30 PN variants on ET 200SP. Plan spare parts accordingly.
• Backward compatibility: The CP 343-1 EX30 is compatible with STEP 7 V5.5 SPx and TIA Portal V13 SP1 onward. Older STEP 7 versions will not configure the EX30 firmware generation.