Configuring PROFIBUS-DP Master/Slave Between S7-300 CPU 313C-2DP

Configuring PROFIBUS-DP Master/Slave Communication Between Two SIMATIC S7-300 CPU 313C-2DP Controllers

The SIMATIC S7-300 CPU 313C-2DP (order number 6ES7 313-6CF00-0AB0 / 6ES7 313-6CE00-0AB0) integrates a PROFIBUS-DP master or slave interface directly on the CPU module, allowing two S7-300 stations to exchange process data without additional communication processors (CPs). This guide consolidates the configuration procedure for a peer-to-peer master ↔ slave link on the integrated DP port (X2), including HW Config setup, NetPro networking, SFC14/SFC15 consistent-data programming, and field verification.

1. System Overview and Topology

The PROFIBUS-DP master/slave link between two CPU 313C-2DP stations uses the second interface (X2) of each CPU. By default, the X2 port is configured as a combined MPI/DP interface that can be switched to pure PROFIBUS-DP mode via HW Config.

1.1 Hardware topology

The two CPUs are connected point-to-point through their integrated PROFIBUS-DP connectors (9-pin Sub-D, female). Termination resistors must be enabled at both physical ends. For a point-to-point link with only two nodes, both terminations must be ON; this is unusual for larger DP networks where only the two ends are terminated.

1.2 PROFIBUS connector pinout (X2, Sub-D female, 9-pin)

2. Prerequisites

Before starting the configuration, confirm the following items are present and compatible.

2.1 Software

• STEP 7 V5.5 + SP4 (or V5.6) — required for CPU 313C-2DP firmware V2.6+
• S7-300 HSP (Hardware Support Package) 0185 or newer installed in HW Config
• Optional: SIMATIC Manager NetPro component (included in STEP 7)
• Optional: NCM S7 for PROFIBUS diagnostics (included in STEP 7)

2.2 Hardware

• 2 × CPU 313C-2DP (6ES7 313-6CF00-0AB0 or compatible)
• 2 × PROFIBUS DP connectors (6ES7 972-0BA12-0XA0)
• 1 × PROFIBUS cable, violet, 2-wire, shielded (e.g., 6XV1 830-0AH10)
• 2 × S7-300 mounting rails (6ES7 390-1AE80-0AA0)
• 2 × PS 307 power supplies (e.g., 6ES7 307-1EA01-0AA0)
• PG/PC adapter USB-PROFIBUS (6GK1 571-0BA00-1AA0 or CP 5711) for commissioning

2.3 CPU 313C-2DP Technical Specifications (from Siemens manual)

3. STEP 7 Project Structure

Create a single STEP 7 project containing both stations. This guarantees consistent PROFIBUS addresses and lets NetPro verify the network topology.

3.1 Create the project

1. Open SIMATIC Manager → File → New → New Project.
2. Right-click the project → Insert New Object → SIMATIC 300 Station — name it CPU_A_Master.
3. Repeat → name the second station CPU_B_Slave.
4. Insert a PROFIBUS network object (Insert → New Object → PROFIBUS) if not auto-created.

4. Master Station Hardware Configuration (CPU-A)

4.1 Insert the CPU in HW Config

1. Open CPU_A_Master → double-click Hardware.
2. From the catalog, insert RACK-300 → slot 1 PS 307 → slot 2 CPU 313C-2DP (6ES7 313-6CF00-0AB0, V3.3).
3. On slot 3–4 add the integrated DI24/DO16 by selecting the CPU's object → Object Properties → tab Inputs/Outputs if not already inserted.

4.2 Configure interface X2 as DP master

1. Double-click the CPU → Interface → select X2 (DP).
2. Click Properties… for PROFIBUS interface X2.
3. In Address: enter address 2, uncheck Subnet if you have not created one.
4. Click New… → create subnet PROFIBUS(1), set transmission rate 1.5 Mbit/s, profile DP.
5. Select DP Master mode.
6. Confirm with OK.

4.3 Configure DP master diagnostic addresses

The CPU reserves two diagnostic address ranges automatically:

5. Slave Station Hardware Configuration (CPU-B)

5.1 Insert the CPU in HW Config

1. Open CPU_B_Slave → Hardware.
2. Insert the same rack and PS 307.
3. Slot 2 → CPU 313C-2DP (6ES7 313-6CF00-0AB0).

5.2 Configure interface X2 as DP slave

1. Double-click the CPU → Interface → select X2 (DP).
2. Open Properties… → assign address 3.
3. Select the previously created subnet PROFIBUS(1) (1.5 Mbit/s).
4. Select DP Slave mode.
5. Confirm with OK.

5.3 Configure slave I/O slots

In DP-slave mode the slave CPU presents its integrated I/O to the master as DP slot modules:

1. In HW Config of the slave project, the CPU object appears with DP-slave identification.
2. Open the DP-slave object → tab Configuration → Slots.
3. For each slot in the slave that should be visible to the master, insert a module from the catalog. The typical mapping for a 313C-2DP:

For exchanging user data only (no I/O mirroring), insert an empty Universal module at slot 1 and configure it with a custom data length, e.g. 8 bytes input / 8 bytes output. This frees up the master CPU's process-image area for arbitrary cross-station mapping.

6. Master Station — Connect the Slave to the Master System

1. Return to HW Config of CPU_A_Master.
2. Select the DP master object (CPU X2).
3. Drag CPU 313C-2DP from the catalog folder PROFIBUS DP → Other Field Devices → S7-300/400 into the master system, or use DP Slave → Connect and select the slave configured in step 5.
4. Confirm PROFIBUS address 3 matches.
5. Open the inserted slave object → tab Configuration → verify slot 1 matches the slave's slot 1 configuration.

7. Save, Compile and Download

1. In HW Config of the master project: Station → Save and Compile (Ctrl+S).
2. Select the CPU → PLC → Download to Target… — choose CPU_A.
3. Repeat for slave station → download to CPU_B.
4. Insert the Micro Memory Card (MMC) into each CPU before power-up if not already fitted.

After download the CPU executes a restart (OB 100). The SF and BF LEDs should extinguish within 5 s. A steady BF LED indicates a PROFIBUS fault — see section 11.

8. Programming — Consistent Data Exchange

Process data exchanged over PROFIBUS-DP between two CPUs can be handled two ways:

8.1 Slave-side — Provide data to master

In the slave CPU (CPU-B), the master writes 8 bytes to slave input area starting at address 0. Use SFC 15 in OB 1 on the slave to copy a data block (e.g., DB 10) into the slave's output process image that the master will read:

// Slave OB 1 - publish 8 bytes from DB10 to master
CALL "DPWR_DAT"
  LADDR  := W#16#0000      // Start address in slave output area (PEW 0)
  RECORD := P#DB10.DBX0.0 BYTE 8
  RET_VAL:= MW 100

8.2 Slave-side — Receive data from master

// Slave OB 1 - receive 8 bytes from master into DB11
CALL "DPRD_DAT"
  LADDR  := W#16#0000      // Start address in slave input area (PIW 0)
  RET_VAL:= MW 102
  RECORD := P#DB11.DBX0.0 BYTE 8

8.3 Master-side — Read slave inputs / write slave outputs

// Master OB 1 - write 8 bytes from DB20 to slave
CALL "DPWR_DAT"
  LADDR  := W#16#0000      // Address of slave output area on master
  RECORD := P#DB20.DBX0.0 BYTE 8
  RET_VAL:= MW 110

// Master OB 1 - read 8 bytes from slave into DB21
CALL "DPRD_DAT"
  LADDR  := W#16#0000      // Address of slave input area on master
  RET_VAL:= MW 112
  RECORD := P#DB21.DBX0.0 BYTE 8

The LADDR value on the master side is the start of the configured I/O area for the slave in the master station. Find it under HW Config → DP master system → slave object → I/O addresses.

9. Alternative — S7 PUT/GET over an S7 Connection

When the application requires variable-length block transfers rather than fixed I/O slots, configure an S7 connection in NetPro and use SFB 14 / SFB 15 (PUT/GET):

1. In NetPro, select the master CPU → Insert New Connection → S7 Connection.
2. Partner: the slave CPU in the same project.
3. Set the TSAP for the slave (default 03.01 for slot 2 rack 0).
4. Download both connection tables.
5. Use SFB 14 PUT (master) / SFB 15 GET (master) with ID := W#16#1 (connection ID from NetPro).

10. Verification

10.1 LED status (CPU 313C-2DP, X2)

10.2 Online diagnostics

1. Connect PG with STEP 7 → PLC → Online → Diagnostics/Setting → Diagnostics of the Slave.
2. Confirm the slave station shows Status OK with current baud rate 1500 kbit/s.
3. Open CPU → Module Information → Diagnostic Buffer on the master. Look for entry 16#0E3F = DP slave OK.

10.3 Functional test

Place a VAT table on both DB 10 (slave send) and DB 21 (master read). Set a non-zero value in DB 10 — confirm it appears in DB 21 within one OB 1 cycle (typically 10–50 ms). Repeat in reverse direction with DB 20 → DB 11.

11. Troubleshooting Matrix

12. Common Configuration Mistakes

1. Using the wrong port. The CPU 313C-2DP has two interfaces — X1 (MPI) and X2 (DP). PROFIBUS-DP must be on X2. Configuring X1 results in no bus activity.
2. Leaving the S7-300 rail terminator OFF. Both physical ends must have ON. For a 2-node link, this means both connectors terminated.
3. Exceeding 244 bytes per direction. The CPU 313C-2DP slave accepts at most 244 bytes input + 244 bytes output per slave, master aggregates across all slaves.
4. Setting baud rate above 1.5 Mbit/s. Although the silicon supports 12 Mbit/s, the S7-300 DP master performance and diagnostics degrade above 1.5 Mbit/s for the CPU 313C generation.
5. Forgetting to download NetPro connection table. When using S7 PUT/GET, both ends need the connection configuration, not only the block calls.
6. Not using SFC 14/15 for multi-word data. Direct peripheral access (e.g., L PEW 0 / T PAW 0) reads/writes word-by-word and may give inconsistent values across multiple words. Use SFC 14/15 for any length ≥ 4 bytes.

13. Performance and Timing

Approximate DP cycle times for a CPU 313C-2DP at 1.5 Mbit/s:

These times exclude STEP 7 OB 1 processing on each side; full end-to-end latency master-DB → slave-DB ≈ 2 × OB 1 cycle + 2 × DP cycle, typically < 100 ms for a 10 ms OB 1.

14. Edge Cases and Field Notes

• Cold restart after MMC swap: When the MMC is replaced, the CPU re-initializes with the new project. The slave must be in RUN and PROFIBUS cable connected before the master is powered, otherwise the master records 0x0EF1 (slave failure) in its diagnostic buffer. Recover by cycling master power.
• Mixed firmware: A 313C-2DP master with firmware V3.3 can communicate with a V2.6 slave. Baud rate is auto-negotiated by the master if Auto is selected — but for stable operation, set explicit 1.5 Mbit/s.
• Adding a CP 342-5: If a third station is required as a DP slave but the CPU's X2 is occupied by another master, use an external CP 342-5 (6GK7 342-5DA02-0XE0) on the IM slot of the slave.
• Hot-swapping the slave: Not supported on S7-300 CPU 313C; if the slave is removed the master logs 0x0E07 and stops cyclic data exchange.
• EMC on long cables: For runs > 50 m, use PROFIBUS EC (fast-connect) cable with grounding clamps every 25 m.

15. Summary Checklist

• [ ] Both CPUs identical 6ES7 313-6CF00-0AB0 or compatible
• [ ] STEP 7 V5.5 SP4+ with HSP 0185

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