PROFINET to PROFIBUS Conversion for S7-300 CPU 313C-2 DP

1. Problem Overview

The SIMATIC S7-300 CPU 313C-2 DP (catalog number 6ES7 313-6CF03-0AB0 for the most common current variant) is a compact PLC with an integrated PROFIBUS DP master/slave port on the front X2 connector. It does not provide an integrated PROFINET interface. When a brownfield installation must connect this CPU to a higher-level PROFINET IO controller (typical S7-1500, S7-1200, ET 200SP CPU, or third-party controller), a bridging component is required.

Three architectural options are available to integrate an S7-300 CPU with an integrated DP port into a PROFINET topology:

1. DP slave mode + IE/PB Link PN IO – the most common, lowest cost approach.
2. CP 343-1 Lean/Advanced – turns the S7-300 station into a PROFINET IO device itself.
3. DP/DP coupler – only relevant when the DP port must remain a master on a third sub-network.

The decision path is driven by three constraints: (a) whether the integrated DP port must keep acting as a DP master, (b) the number of PROFIBUS slaves behind the CPU, and (c) the maximum allowable cyclic data length on the PROFINET side. The Siemens reference manual Connecting PROFIBUS to PROFINET documents the hybrid topology explicitly.

2. Prerequisites and Topology Constraints

Before selecting hardware, verify the following items in the existing installation.

PROFINET cycle time must be at least 1 ms and an integer multiple of 31.25 µs. The IE/PB Link PN IO accepts IO cycle times of 1 ms and above; below 1 ms the link reports a parameterization error.

3. Option 1 — DP Slave Mode + IE/PB Link PN IO

This is the recommended, lowest-effort path when the integrated DP port is not strictly required as a master.

3.1 Hardware

• IE/PB Link PN IO (catalog 6GK1 412-1BA10 for the standard variant; the 6GK1 412-1BA10-0AA0 module supports both PN IO controller and device modes). It converts a PROFIBUS DP master on its lower RS-485 port into a PROFINET IO device on its upper RJ-45 port.

3.2 Topology

The 313C-2 DP is configured as a DP slave (I-slave) on its X2 port. The IE/PB Link PN IO acts as the DP master toward the CPU and as the PROFINET IO device toward the upper-level PN controller. From the PN controller's perspective, the entire PROFIBUS sub-network — including the 313C-2 DP and any DP slaves attached to the CPU — appears as a single PROFINET IO device.

[PN Controller S7-1500]
   |  PROFINET (RJ-45, 100 Mbit/s)
[IE/PB Link PN IO  6GK1 412-1BA10]
   |  PROFIBUS DP (RS-485, 9-pin D-sub)
[CPU 313C-2 DP  6ES7 313-6CF03-0AB0]
   |  PROFIBUS DP (optional expansion)
[ET 200M / DP slaves ...]

3.3 STEP 7 Configuration Sequence

1. Open the S7 project containing the CPU 313C-2 DP.
2. Right-click the CPU in HW Config → Object Properties → DP Interface → tab Operating Mode. Select DP Slave and assign the diagnostic address (default 1023).
3. Under DP Slave configuration, add slots matching the data exchange layout. The slot 0 always contains the diagnostic module; subsequent slots contain the input/output data area (1 byte to 32 bytes per slot, maximum 244 bytes total input + 244 bytes total output for the 313C-2 DP).
4. Install the IE/PB Link PN IO from the hardware catalog (path: PROFINET IO → Gateways → IE/PB Link PN IO). The GSD file ships with STEP 7; if missing, install via Options → Install GSD File.
5. Insert the IE/PB Link into the PN subnet and assign a PROFINET device name (e.g., ie-pb-link-01) and IP address (e.g., 192.168.0.10).
6. On the PROFIBUS side of the link, set the operating mode to DP Master and the baud rate to 1.5 Mbit/s (default). Connect the CPU as a DP slave under the link.
7. Compile and download the HW Config to the CPU. The PN controller will see one IO device representing the IE/PB Link, which transparently forwards all DP I/O.

3.4 Programming Notes (FC11/FC12)

For PROFINET IO device mode on a SIMATIC controller, Siemens supplies FC11 (PN_IO_RECV) and FC12 (PN_IO_SEND) in the standard library "PROFINET IO". On the S7-300 side acting as a DP slave, no FC11/FC12 calls are required — the data exchange is pure process-image I/O through the PN controller's slot configuration. FC11/FC12 only become necessary if the S7-300 itself is configured as a PN IO device (Option 2).

4. Option 2 — CP 343-1 as PROFINET IO Device

When the S7-300 must function as a PROFINET IO device in its own right — for example because it must publish its data into a PROFINET controller's process image with dedicated slot-level diagnostics — a CP 343-1 Lean or Advanced module is added to the backplane.

4.1 Hardware

All three support PROFINET IO Device with up to 16 IO sub-slots. The CP is plugged into any free slot of the S7-300 rack (slots 4–11), occupying 1 slot width.

4.2 Configuration

1. Insert the CP 343-1 from the hardware catalog under SIMATIC 300 → CP 300 → Industrial Ethernet.
2. Open Properties of the CP → tab PROFINET Interface. Enable IO Device, assign an IP address (e.g., 192.168.0.20) and a PROFINET device name.
3. Add IO slots. Each slot maps to a configured input/output length in the PN controller's device view. Slot 0 is reserved for diagnostics; slot 1 is the first user slot.
4. Download the HW Config to the CPU. The CP automatically starts PROFINET IO AR (Application Relationship) establishment with the configured controller.

4.3 Reading and Writing Data via FC11/FC12

The CP 343-1 only exposes the PN data to the S7-300 user program via FC11 and FC12. Example call in STL/English:

// Write 10 bytes to PN IO slot 1, sub-slot 1
CALL  FC12  // PN_IO_SEND
   IOID    := 0           // Local PN interface ID, 0 = first CP
   LADDR   := W#16#0100   // Logical base address of slot 1 (256)
   LEN     := 10          // Send length
   SEND    := P#M 100.0 BYTE 10
   DONE    := M 200.0
   ERROR   := M 200.1
   STATUS  := MW 202

// Read 10 bytes from PN IO slot 1, sub-slot 1
CALL  FC11  // PN_IO_RECV
   IOID    := 0
   LADDR   := W#16#0100
   LEN     := 10
   RECV    := P#M 120.0 BYTE 10
   NDR     := M 210.0
   ERROR   := M 210.1
   STATUS  := MW 212

The STATUS word is interpreted per the Siemens Industry Online Support PN IO error table; common return values include 0x0000 (no error), 0x8080 (slot length mismatch), 0x80A1 (AR not established), and 0x80C0 (sub-module not configured).

5. Option 3 — DP/DP Coupler (Master-to-Master Bridge)

The DP/DP coupler (catalog 6ES7 158-0AD01-0XA0) is required only when both DP ports must remain DP masters. Two DP masters exchange a fixed data image across the coupler — there is no S7-300 user program involvement in the data forwarding itself. The 313C-2 DP would still need a way to reach PROFINET, so this option usually requires two bridges: the DP/DP coupler between the two DP segments, plus an IE/PB Link or CP 343-1 to expose that data to PROFINET.

5.1 Hardware Configuration

The DP/DP coupler has two DB-9 ports, each acting as a DP slave to the masters on either side. Maximum data throughput is 244 bytes input + 244 bytes output per direction, with a propagation delay under 5 ms at 12 Mbit/s. Configuration is performed by setting DIP switches on the front for the maximum data length per direction (32, 64, 128, or 244 bytes); this setting must match on both coupler sides.

5.2 Why It Is The Least Favourite

Adding two gateways introduces two points of failure and roughly doubles the diagnostic complexity. The data image is fixed in advance; reconfiguring I/O requires a physical DIP switch change. Use only when the existing DP master absolutely cannot be reconfigured.

6. Third-Party Gateway Alternatives

When Siemens-specific components are not available, certified third-party gateways from HMS Networks and Moxa provide equivalent bridging.

• Anybus Communicator ABC4023-A (HMS product page) — PROFINET IO Device to PROFIBUS DP Device, configuration via web interface, conversion time typically 20 ms.
• NT 50-DP-EN (PI product finder) — PROFIBUS DP master to PROFINET IO device, sub-20 ms conversion, DIN-rail compact form factor.
• Moxa MGate series (Moxa protocol gateways) — broader protocol coverage including Modbus RTU/TCP to PROFINET/PROFIBUS bridging; useful when Modbus is in the mix.

Third-party gateways ship with their own GSDML/GSD files and must be installed separately into the engineering tool. PROFINET certification is granted by PI (PROFIBUS & PROFINET International) and the device receives a certificate number visible on the GSDML header; verify before deployment in critical segments.

7. GSD File Installation and Device Naming

Each PROFINET device requires a GSDML file (General Station Description Markup Language, XML-based); PROFIBUS devices use the older GSD format. Installation paths:

• STEP 7 V5.x: Options → Install GSD File → browse to the .gsd or .xml → restart HW Config.
• TIA Portal: Options → Manage general station description files (GSD) → select the source folder → Install.

Assigning a PROFINET device name programmatically is also possible via the DCP protocol (Discovery and Configuration Protocol). Use the Siemens PRONETA tool (Siemens Support) for an offline-friendly assignment procedure that does not require TIA Portal open.

8. Diagnostics and Troubleshooting

The following table summarises the most common fault conditions observed during commissioning of an S7-300-to-PROFINET bridge.

8.1 Diagnostic Buffer on S7-300

Open Online → Accessible Nodes → CPU 313C-2 DP → Diagnostic Buffer. Typical entries during a bridge configuration error:

• "DP Slave failure on slot X" — slot not configured on the DP master side.
• "Parameterization error on DP Slave" — slot length mismatch or wrong GSD revision.
• "PROFINET IO: AR establishment failed" — device name or IP mismatch.

8.2 LED Status Indicators

On the IE/PB Link PN IO, the front LEDs report: SF (red) = group error, BF (red) = bus fault on PROFIBUS or PROFINET side (flashing), LINK (green) = Ethernet link up, RX/TX (yellow) = traffic. The CP 343-1 has equivalent LED indicators with SF and BF providing the same fault reporting.

9. Specifications Comparison

10. Recommended Topology by Scenario

11. Field-Commissioning Checklist

1. Verify all device names and IP addresses are unique on the PROFINET subnet.
2. Confirm D-sub connector pin-out (PROFIBUS pin 3 = data B, pin 8 = data A; never swap).
3. Power up the PN controller before the IE/PB Link so AR establishment completes during link startup.
4. Use STEP 7 / TIA Portal online diagnostics to verify all DP slaves are reached.
5. Capture a wire trace of the first PROFINET start-up using Wireshark and the PROFINET dissector; confirm AR establishment, IO data CR, and record CR are all visible.
6. Set the watchdog on the IE/PB Link to ≥ 3 × the PN send clock to absorb normal jitter.
7. Document the PROFINET device names and IPs in the project documentation; PROFINET device names are not exported by HW Config — they must be assigned to the physical device and stored as part of the commissioning record.