Configuring S7-313C-2DP MPI and PROFIBUS Ports for WinCC and DP

Overview

The SIMATIC S7-300 CPU 313C-2DP is a compact controller with two physically separate communication ports, a default MPI/DP combined port (X1) and a fixed PROFIBUS-DP port (X2). This dual-port topology is the single most important architectural detail when a user wants to drive a PROFIBUS-DP master line to ET200S stations while simultaneously exchanging process data with a WinCC SCADA station and/or a third-party DCS. Engineers routinely assume the second port is locked to one role; in practice both ports support configurable protocols and the controller can run a mixed configuration as long as bus parameters, addresses, and slot assignments are kept unambiguous.

This reference covers the exact port capabilities, the rule set for using the MPI port as a DP slave, the connection options for WinCC over MPI, the practical limits of adding a third-party DCS on the same physical wire, and the STEP 7 / TIA Portal commissioning sequence with diagnostic checks.

CPU 313C-2DP Hardware Architecture

The CPU 313C-2DP is offered under several order numbers that are firmware- and feature-compatible but differ in delivery date and on-board I/O. The two commonly encountered variants are:

Both variants share the same dual-port topology: Port 1 (X1) is a combined MPI/DP interface, Port 2 (X2) is a fixed PROFIBUS-DP interface. The integrated I/O is addressed in the process image like any S7-300 digital module. Full technical specifications are documented in the official Siemens "SIMATIC S7-300 CPU 31xC and CPU 31x: Technical specifications" manual available on the Siemens SiePortal entry for the 31xC family.

Integrated I/O and Counter Resources

The on-board digital I/O and the integrated counters are configured as part of the S7-300 hardware catalog in HW Config / TIA Portal device configuration. Counter resources are limited and must be reserved before assigning high-speed counting tasks:

These resources are independent of the communication ports, but engineers should verify them when planning migration from a 313C (no DP) or 314C-2DP, because counter and DI/DO budgets differ between compact CPU families.

Port Interface Specifications

The two physical ports on the CPU 313C-2DP use 9-pin D-sub female connectors (RS-485 physical layer). The connector pin-out and the PROFIBUS termination rules are identical between MPI and DP operation because both protocols use the same physical layer.

The crucial point is that Port 1 is multi-mode. Its protocol is selected at hardware-configuration time (HW Config in STEP 7 V5.x, or Device Configuration in TIA Portal). Changing the role requires re-downloading the hardware configuration, but the role is otherwise freely selectable within the firmware capability of the CPU.

PROFIBUS Cabling Rules

Both ports must be terminated when they sit at the physical ends of a segment. Use active RS-485 PROFIBUS terminators or the standard PROFIBUS connector with integrated termination that is switched ON at the first and last node. A typical mixed configuration uses two segments:

• Segment 1 (DP master line): X2 → CP/connector → ET200S IM151-1 stations in linear topology. Baud 1.5 Mbps is a safe default for cable lengths under 50 m.
• Segment 2 (MPI line): X1 → CP5611/CP5613 A2/CP5621 on the SCADA PC. Maximum 32 nodes per segment, 127 with repeaters, but the practical limit for a stable WinCC link is under 16 nodes.

MPI Port Modes and Capabilities

The MPI port (X1) of the 313C-2DP supports three operating modes, selectable in HW Config / TIA Portal under "Interface → Properties":

1. MPI mode (default). Multi-point interface for PG, OP, WinCC, and S7-S7 communication. Default baud rate 187.5 kbps. Maximum of 32 active stations per bus segment (MPI address range 0 to 31, with 0 reserved for programming device). The S7-300 CPU occupies one MPI address (default 2).
2. DP master mode. Configures X1 as a second PROFIBUS-DP master line. Useful when an installation needs two physically separate DP trunks (for example, two lines of ET200S that must not share bus parameters or fault domains). In this mode, X1 cannot simultaneously carry MPI traffic.
3. DP slave mode. Configures X1 as a PROFIBUS-DP slave that responds to a higher-level DP master. This is the mode relevant to the question of using the MPI port to talk to a third-party DCS that expects the S7 to appear as a slave on a DP line.

PROFIBUS DP Port Modes (X2)

Port 2 of the 313C-2DP is dedicated to PROFIBUS-DP and supports DP master operation only. The CPU cannot be configured as a DP slave on X2. This is a hardware/firmware restriction of the 313C-2DP, not a configuration option. If a higher-level PROFIBUS master is required, the user must choose a different CPU family (such as the ET200S IM151-8 PN/DP as an alternative slave, or a 315-2DP/PN, or 317-2DP/PN) or add a CP342-5 that does support DP slave mode.

Standard DP master parameters on X2 of the 313C-2DP:

Simultaneous Operation: DP Master on X2 + MPI on X1

This is the configuration the original poster needs and it is the most common field deployment of the 313C-2DP:

• X2 = DP master → ET200S distributed I/O. Standard PROFIBUS-DP, 1.5 Mbps typical, ET200S IM151-1 as the slave.
• X1 = MPI → WinCC SCADA PC (with CP5611/CP5613/CP5621) and optionally a third-party DCS that speaks the S7 MPI protocol.

The two ports use independent protocol stacks inside the CPU. The S7-300 firmware schedules communication jobs in cyclic OB1 plus the background communication. As long as the total connection count does not exceed the CPU's connection resources (resource budget = 8 connections for a 313C-2DP, with 1 reserved for PG and 1 for OP by default), both ports run concurrently without interaction.

Connection Resource Budget (CPU 313C-2DP)

WinCC via the S7 Protocol Suite (MPI) typically consumes 1 connection. A third-party DCS also typically consumes 1 connection. With PG + OP + 2 application connections, the budget is fully used; an additional S7-S7 connection (for example a peer 313C via MPI) will fail at connection establishment with a "no connection resources" diagnostic buffer entry.

WinCC Communication Setup via MPI

WinCC connects to a 313C-2DP on MPI using the S7 Protocol Suite channel. In WinCC Explorer:

1. Add a new driver → "SIMATIC S7 PROTOCOL SUITE".
2. Under "MPI" right-click → "New Driver Connection".
3. Set the MPI address of the S7-300 CPU (default 2) and the MPI address of the WinCC PC station (must be unique on the segment, for example 5).
4. Select the slot of the CPU (slot 2 in S7-300, this is fixed for the 313C-2DP rack 0).
5. Create tags. Each tag maps to a DB, M, I, or Q area. The WinCC tag address uses the S7 syntax DBx,Byte y Bit z.

The reference for parameter assignment and channel diagnostics is the "WinCC Communication" manual, published by Siemens for the matching WinCC version. The current online manual and the version-specific PDFs are available through the Siemens Industry Online Support portal. Interface-level information (which MPI baud rates are supported, which CP cards are recommended on the PC side) changes little between WinCC versions; the procedure above applies from WinCC V7.0 onward and to the TIA-portal-based WinCC (WinCC Professional / Comfort) where the equivalent channel is "SIMATIC S7-300/400" under "SIMATIC S7 Protocol Suite".

PC-Side Hardware for MPI

For SCADA, use a PCIe CP card, not the USB adapter. The USB adapter is rated for diagnostic/commissioning and will saturate the bus at the data rates WinCC requires.

Third-Party DCS Connectivity on the MPI Port

The MPI protocol of the S7-300 is a Siemens-proprietary implementation over RS-485. A third-party DCS can communicate with the 313C-2DP on MPI only if it speaks the S7 MPI protocol stack (sometimes called the S7-MPI driver, available from a number of third-party SCADA/DCS vendors). It is not a public Modbus, not Profinet, and not HART — those protocols do not run on the MPI pins of an S7-300.

If the third-party DCS can act as a passive S7 client (driver available from vendors such as your SCADA vendor's S7-MPI option) it can be connected as another node on the MPI segment, sharing the bus with WinCC and the PG. Each device consumes one MPI address and one CPU connection resource.

Can the MPI Port Be a DP Slave?

Yes — the X1 port of the 313C-2DP can be set to DP slave mode. In that role the CPU appears as a PROFIBUS-DP slave on the segment driven by an external DP master. This is the correct way to let a third-party DCS (that has a PROFIBUS-DP master port) read/write process data on the 313C-2DP. The trade-off is that the CPU is no longer reachable over MPI for WinCC or PG on X1.

To make the third-party DCS the PROFIBUS-DP master and the 313C-2DP a DP slave on X1, follow this hardware configuration:

1. Open HW Config in STEP 7 (or device configuration in TIA Portal) and select the CPU 313C-2DP.
2. Open "Properties" on the X1 (MPI/DP) interface.
3. Select "PROFIBUS-DP" as the interface type and "DP slave" as the operating mode.
4. Configure the slave address on the DP master line (for example 3, leaving 1 for the DCS master and 2 for the original 313C-2DP master on X2 if X2 is still used).
5. In "Configure" → assign the diagnostic, input, and output slots that the external master will read/write. The slots are mapped into the S7-300 I area on byte boundary; the default mapping is 0–3 in/out on slot 0 and slot 1.

Simultaneous DP Master (X2) + DP Slave (X1)

The 313C-2DP can run X2 as DP master for ET200S and X1 as DP slave for the third-party DCS. This gives two physically independent PROFIBUS segments. The CPU is the master on one and a slave on the other. There is no firmware restriction against this combination. Confirm by checking that the S7-300 connection resources are not exhausted by the additional S7 connections required by the slave/master configuration (DP slave mode does not consume S7 connections, but PG and OP reservations do).

STEP 7 / TIA Portal Configuration Procedure

The following procedure applies to STEP 7 V5.5 + WinCC flexible / WinCC V7.x. The TIA Portal equivalent uses "Device Configuration" and the same conceptual dialogs.

Prerequisites

• STEP 7 V5.5 SP4 or later (or TIA Portal V14 SP1 or later for the 6CG04 firmware variant).
• WinCC V7.0 SP3 or later (or the TIA-portal-based WinCC Professional V14 SP1 or later).
• CP5611/CP5613/CP5621/CP5623 installed in the SCADA PC; the "SIMATIC NET" software installed with the CP card, with the MPI driver enabled.
• The GSD file for the ET200S IM151-1 station in the PROFIBUS-DP master segment, or use the Siemens "ET200S" station type in the HW catalog.

Step-by-Step

1. Create the S7-300 station in STEP 7 / TIA Portal. Insert the rack, slot 1 power supply (or use the integrated 24 V supply of the 313C-2DP), slot 2 CPU 313C-2DP, slot 3–8 I/O modules as required.
2. Configure the X2 (DP) port as DP master. Set the master address (default 2). Set the baud rate (1.5 Mbps typical). Under "Subnet" create a PROFIBUS subnet (for example, PROFIBUS(1)).
3. Add ET200S stations to the subnet. Drag the "ET200S" → "IM151-1" from the catalog. Assign a unique slave address (for example 3, 4, 5). Configure the slot mapping for DI/DO modules. Save and compile.
4. Configure the X1 (MPI/DP) port:
   • If connecting to WinCC only: keep the default MPI mode, address 2, baud 187.5 kbps (or 1.5 Mbps for higher throughput). Under "Subnet" create an MPI subnet (or leave it unconnected if the PG/SCADA connection is point-to-point).
   • If connecting to a third-party DCS as a DP slave: change interface type to PROFIBUS-DP, operating mode "DP slave". Set the slave address. Add the slave-to-master mapping under "Configuration".
5. Save and download the hardware configuration to the CPU. After download, the CPU runs a restart; observe the diagnostic buffer for the message "Interface X1: MPI active" or "Interface X1: DP slave active".
6. Configure WinCC:
   • In WinCC Explorer, right-click "Tag Management" → "Add New Driver" → "SIMATIC S7 Protocol Suite".
   • Open the "MPI" channel node, right-click → "New Driver Connection" → set PLC address = 2 (or the configured address), set PC MPI address = 5 (or another free address on the bus).
   • Add tags under the connection. Map to the S7 areas: DB, M, I, Q.
   • Run the WinCC "Channel Diagnosis" tool from SIMATIC NET to confirm the connection is up. The tool shows a green status for each configured connection.

Verification

1. In STEP 7, "PLC → Online → Monitor/Modify" on a tag. Confirm the value updates while WinCC is connected.
2. In WinCC, open Graphics Designer, place an I/O field on a screen, and verify the value updates cyclically.
3. In WinCC "Channel Diagnosis" (under SIMATIC NET) confirm the S7 connection is "established" and the byte counters are incrementing.
4. In the CPU diagnostic buffer, verify that no SF/DP errors are logged (only the standard "Module OK" entries from the ET200S stations).
5. Force a value in STEP 7. Verify WinCC receives the change within one WinCC update cycle (default 1 s, configurable down to 250 ms on WinCC V7.4+).

Diagnostics and Verification

The CPU 313C-2DP exposes a comprehensive diagnostic buffer accessible via STEP 7 / TIA Portal online. The key event IDs to look for during a mixed-port installation:

Port LED Meanings on the CPU 313C-2DP

When BF1 is on steady (not flashing), the typical cause is that no node on the X1 segment is responding — either the SCADA PC is offline, the cable is open, or the configured MPI address does not exist on the bus. When BF1 flashes, traffic is reaching the bus but responses are inconsistent (often baud rate mismatch).

Troubleshooting Matrix

Field-Commissioning Checklist

1. Verify CPU order number matches the GSD / catalog entry being used in HW Config (313C-2DP vs 313C-2PtP are different CPUs).
2. Verify each MPI/DP node on the bus has a unique address (1–32 for MPI, 1–126 for DP, with 0 reserved for PG service).
3. Confirm only the two end nodes of each segment have termination enabled.
4. Download HW Config and confirm the CPU diagnostic buffer shows "Restart executed" without subsequent SF/DP errors.
5. Run the "Commissioning → Online & Diagnostics → PROFIBUS" check in TIA Portal (or equivalent in STEP 7 V5.x) to enumerate reachable slaves on each segment.
6. From the PC, run the SIMATIC NET "Set PG/PC Interface" test to confirm the CP card can be pinged at the MPI address.
7. In WinCC, run "Channel Diagnosis" to confirm each configured connection is "established" and stable for at least 5 minutes.
8. Force a known value in STEP 7 and verify it appears in WinCC within one update cycle.

Notes on Migration and Variants

If the application is being migrated or duplicated, be aware that the 313C-2DP variants differ slightly in the on-board I/O update rate and in the maximum number of S7 connections supported in newer firmware revisions. The 6CG04 variant has updated firmware that supports more diagnostics and is recommended for new installations. Both variants are pin-compatible and program-compatible; the same S7 program runs on both with no changes.

If the system design requires a DP slave on the MPI port and an Ethernet connection to WinCC, a more modern alternative is the 315-2PN/DP or 315-2DP/PN, both of which have an integrated PROFINET interface and a DP port. The PROFINET interface carries WinCC tags over TCP/IP using the S7 Protocol Suite "Named Connection" or "TCP/IP" channel. For a long-term recommendation, PROFINET is preferred over MPI for new installations because cable lengths, addressing, and SCADA integration are simpler.