Configuring S7-315-2DP as Profibus Slave to S5 CPU 948 Master

Overview

Integrating a stand-alone SIMATIC S7-315-2DP into a legacy SINEC L2 network as a Profibus DP slave is a common migration step when an existing S5-948 master plant must be expanded without replacing the controller. SINEC L2 was the original Siemens branding for Profibus DP (EN 50170 / IEC 61158) and is fully interoperable with Profibus-DP networks of today, provided the correct bus parameters, GSD, and handshake structures are observed on both sides.

This procedure uses the classic tool chain: COM PROFIBUS on the master (S5) side and STEP 7 V5.x / SIMATIC Manager on the slave (S7) side. The result is a deterministic, cyclic Profibus-DP data exchange between the S5 CPU 948 (typically via an IM 308-C master interface) and the S7-315-2DP integrated DP port.

Prerequisites

For a full reference of the S5 Profibus interface handling, see the SINEC L2 Interface of the S5-95U Programmable Controller manual (6ES5 998-8MB22), which contains bus parameter defaults still applied in the S5-948 / IM 308-C era. The original Siemens Support entry ID 113652 is the official repository for SIMATIC S7 / S7-300 GSD files and remains the canonical download point for SIEM089D.GSD and successor files.

Network Architecture

The classic topology for this integration is a single Profibus-DP segment with the IM 308-C acting as class 1 master. The S7-315-2DP is attached as a DP slave. A typical wiring is shown below.

   +-------+        IM 308-C        +------------------- Profibus DP (RS-485) -------------------+
   | S5    | (6ES5 308-3UC11)       |                                                            |
   | 948   +-------+-------+        |                                                            |
   |       |  S5  |  DB1  |        |                                                            |
   |       | PROG.|  SYS  |        |                                                            |
   +-------+-------+-------+        |  9.6 kBaud ... 12 MBaud                                   |
       |                            |      (default 1.5 MBaud)                                  |
       | AS511                      |                                                            |
       v                            v                                                            v
   +------+                   +--------+    +--------+    +--------+                          +--------------+
   |  PG  |                   | IM308C |----| Term.  |----| ET200M |---- ... ---- (segment)-----| S7-315-2DP   |
   +------+                   | Mstr #1|    |  ON    |    | slaves |                             | (X2) slave #X|
                             +--------+    +--------+    +--------+                             +--------------+

Key topology rules:

1. One bus terminator ON at the first and last physical node; all other nodes OFF.
2. Maximum of 32 stations per segment; repeaters required beyond 32 nodes or 1000 m at the chosen baud rate.
3. Default baud rate for legacy SINEC L2: 1.5 MBaud with 187.5 kBaud fallback. Match this on both COM PROFIBUS and STEP 7 HW Config.
4. Profibus addresses: master = 1, S7-315-2DP slave = a free address (typically 3, 4, 5...). Avoid address 0 (PG service) and address 1 (master) and address 126 (default for unconfigured slaves).

Step 1 - Acquire the Correct GSD File for the S7-315-2DP

The S7-300 GSD file is the bridge that allows the S5 COM PROFIBUS tool to expose the S7-315-2DP as a virtual slave station. Each CPU firmware variant has its own GSD.

1. Open the Siemens support portal and navigate to entry 113652 "GSD files for SIMATIC S7".
2. Identify your S7-315-2DP order number (printed on the front, e.g., 6ES7 315-2AG10-0AB0) and the firmware release (read with STEP 7 in PLC > Module Information or via the front selector).
3. Download the matching GSD. Common files used in this configuration:
   • SIEM089D.GSD - early 315-2DP (firmware V1.x / V2.x).
   • SI80F0C0.GSD - 315-2AH10 / 2AH14 with Profibus DP-V0 slave support.
   • S7_3152AG.GSD - newer variants (firmware V3.x).
4. Place the GSD (and matching .BIT bitmap if present) in the COM PROFIBUS import directory, e.g., C:\ComProfibus\GSD or CPBV5x\GSDFILES depending on the tool version.

Step 2 - Configure the S5-948 + IM 308-C Master in COM PROFIBUS

COM PROFIBUS (V5.1 or later, install from the original "COM PROFIBUS V5.x" disc or from entry ID 113652 supplementary package) builds the binary master configuration consumed by the IM 308-C at startup.

1. Launch COM PROFIBUS. File > New > Master system; select IM 308-C as master type and S5-95U/948 as host. Set master Profibus address = 1.
2. Import the GSD: Options > Install GSD. After installation, the S7-300 family appears in the catalog tree.
3. Drag the S7-315-2DP slave from the catalog into the bus line. Assign a free Profibus address (e.g., 3).
4. Define the I/O slot configuration. The S7-315-2DP exposes the following default slot 0 modules (you may add/remove per project):
   • Slot 1: 32 DI (inputs from the master perspective)
   • Slot 2: 32 DO (outputs to the slave)
   • Slot 3: AI 8x12Bit / 16 words diagnostic
5. Open Bus parameters tab. Set:
   • Baud rate: 1.5 MBaud (or 187.5 kBaud for long cables / legacy hubs).
   • Slot time (T_SL): 1000 bit-times at 1.5 MBaud.
   • Min slave interval (min T_SDR): 11 bit-times.
   • Max slave interval (max T_SDR): 150 bit-times.
   • Quiet time (T_QUI): 0.
   • Setup time (T_SET): 1 bit-time.
6. File > Save, then File > Export to binary. Output is the file COMDB.TXT / *.2BF (binary configuration) for the IM 308-C.

For a complete sample configuration with a 315-2DP slave, see Siemens Support entry ID 6709721 "Sample configuration: IM 308-C master with S7-300 slave". The same bus parameters and slot layout also apply to the S5-948 host CPU.

Step 3 - Transfer the Configuration to the IM 308-C

1. Connect the PG to the S5-948 using an AS511 cable (COM1, 9600 8E1) or via the IM 308-C programming interface.
2. Use COM PROFIBUS > PLC > Download to IM 308-C. The tool erases the flash on the IM 308-C and writes the .2BF binary. Wait for the green "RDY" LED on the IM 308-C to return to a steady state.
3. Cycle power on the S5-948 rack so the IM 308-C re-initializes with the new configuration.

Step 4 - Configure the S7-315-2DP Slave in STEP 7

The S7 side must be told it is a slave on its X2 port, with the same address and baud rate as the master, and a slot configuration that matches COM PROFIBUS exactly.

1. Open the S7 project in SIMATIC Manager. Open HW Config for the S7-300 station.
2. Double-click the DP row of the S7-315-2DP (X2). In the dialog set:
   • Operating mode: DP slave.
   • Profibus address: 3 (must match COM PROFIBUS).
   • Baud rate: 1.5 MBaud.
   • Subnet: the same subnet defined for the master (or create a new one and align via Properties > Network).
3. In the Configuration tab add the same slot modules that COM PROFIBUS uses, but mirrored: COM PROFIBUS sees the S7 as inputs/outputs from the master side; STEP 7 sees them as outputs/inputs on the slave side. The I and O directions must be opposite between the two tools.
4. Compile and download HW Config to the S7-315-2DP via MPI/Profibus.

Step 5 - Configure the S5-948 DB1 System Data Block

The S5-948 / IM 308-C pair uses the system data block DB1 for two purposes: (a) the IM 308-C configuration pointer, and (b) the user-visible I/O image for the cyclic data exchange. Without DB1, the CPU 948 will not see the data of the S7-315-2DP at the configured P/Q addresses.

1. In the S5 programming tool (STEP 5 / S5-DOS), open the project of the S5-948.
2. Create or open DB1. Place the following data structure (the exact syntax follows the IM 308-C handling blocks described in entry ID 1142470, section 6.1):

   DB1     // System data block for IM 308-C / Profibus-DP
   
         0   KC    'IM308C'   // Identifier (8 chars)
        +8   KC    'S5DP'     // Protocol / role
       +16   KF    +1         // Master number
       +20   KF    +1         // Slot 0: 1 = active, 0 = passive
       +24   KF    +0         // Reserved
       +28   KF    +0         // Diagnostic address base
       +32   KF    +3         // Profibus address of the S7-315-2DP
       +36   KF    +32        // Number of input bytes from the slave
       +40   KF    +32        // Number of output bytes to the slave
       +44   KF    +0         // Reserved
       +48   KH    0000       // Status word 1
       +52   KH    0000       // Status word 2
       +56   KF    +0         // Reserved
       +60   KF    +0         // Reserved
       +64   KC    'END'      // End marker

3. The diagnostic address +28 must match the analog or digital input word the IM 308-C is wired to in the S5 I/O area (PII / PIQ). Typical default base address for IM 308-C: PIW 128 / PQW 128. Adjust to your project's address map.
4. Save DB1 and download to the S5-948.
5. Set the IM 308-C's rotary switch to RUN, then power-cycle the rack so the IM 308-C reads the new .2BF configuration and DB1 is consistent.

Step 6 - Assign Diagnostic and I/O Addresses

Keep the byte counts and module IDs identical on all three views. STEP 7 will not compile if the slave I/O length disagrees with the master's view; COM PROFIBUS will warn if the slave device name or address duplicates an existing station.

Step 7 - Verification and Commissioning

1. Power up the S5-948 rack first, wait for the IM 308-C RDY LED to go steady green and the SF LED to remain off.
2. Power up the S7-315-2DP. The DP port LEDs should be: ON (green, bus voltage), BF (off), SF (off) within 5 seconds. A flashing BF indicates no parameter assignment from the master; a steady BF indicates parameter assignment failed (compare GSD, address, baud rate).
3. From the S5 PG, go online in COM PROFIBUS or STEP 5. In the IM 308-C Diagnostics view, confirm the S7-315-2DP appears with status Data Exchange (green).
4. From the STEP 7 side, in HW Config right-click the DP port and select Operating Mode > Monitor/Modify. Force a known pattern in the S7 process image outputs; verify it appears in the S5 PII. Reverse: write to the S5 PIQ and read in the S7 I image.
5. Document the parameter telegram and the diagnostic telegram with COM PROFIBUS > Diagnostics > Save. Save the STEP 7 project and the S5 program (including DB1) to a versioned archive.

Troubleshooting Matrix

Migration Path Beyond the S5-948

The S5-948 / IM 308-C combination reached end-of-service well before the modern Profibus-DP V1/V2 era. When a plant reaches its end of life, the typical migration is to replace the S5-948 with a S7-300 / S7-400 / ET200S master, then keep the S7-315-2DP as a slave, or upgrade the whole segment to Profinet. For greenfield Profibus segments today, Siemens promotes the SINEC Advanced Network Suite for network management, with configuration best-practices documented in the TIA Portal Scalance configuration guides. The S5-95U SINEC L2 manual 6ES5 998-8MB22 remains the most accurate reference for the bus-parameter math and the original SINEC L2 / Profibus-DP interoperability rules that this S7-315-2DP integration still relies on.

FAQ