STARTER Routing via S7-300 MPI: Drive Access Configuration

Routing Architecture: STARTER, S7-300, and SINAMICS Drives

STARTER is the Siemens commissioning tool for the SINAMICS drive family — covering G110, G120, G120C, G120D, G120P, G130, G150, S110, S120, S150, and SINAMICS MV. STARTER normally reaches a drive over its native bus interface: PROFIBUS DP via the Control Unit's X126 or X136 connector, PROFINET via X150, or a serial USS link on the older G110/G120 units. When the engineering PC is not on the same physical network as the drive, but is connected to the project through an S7-300 CPU, the CPU must act as a router between the two segments. The PC attaches to the CPU's MPI port (or to the Ethernet interface of an integrated PN CPU or a CP), STARTER issues a routed online request, and the S7-300 firmware forwards the request to the drive bus. This is S7 routing.

Two architectural conditions must be satisfied before routing functions:

1. The drive must exist as a PROFIBUS DP slave or PROFINET IO device under the S7-300 CPU in the STEP 7 / SIMATIC Manager hardware configuration (HW Config). If the drive is configured as a peer station at the same level as the CPU, the routing path is not established and STARTER reports "No target station found" or "Online connection cannot be established". In that case Drive ES Basic or Drive ES PCS 7 is required to integrate STARTER as a child project of STEP 7.
2. STARTER must use the S7ONLINE access point, not the direct DRIVE interface. Selecting the wrong access point is the single most common commissioning error on this topology and is the root cause of the symptom described in field reports where the engineer is "online on PLC by MPI" but STARTER still cannot reach the drive.

The complete routing procedure is documented in the Siemens application summary "How do you configure S7 routing for STARTER?" available at Siemens Support Entry 2383206. The PG/PC-side procedure is also described in the STARTER commissioning manual at Siemens Support Entry 26202408 and the S7-300 CPU 31x manual collection at Siemens Support Entry 12996906.

Topology and Reference Network

The reference topology uses a single S7-300 CPU with an MPI port and a PROFIBUS DP master port. The PC connects to the CPU's MPI connector, the drive sits on PROFIBUS DP behind the CPU. The CPU forwards routing telegrams between the two segments. With a PN/DP CPU (for example 315-2 PN/DP) the same CPU can additionally act as a PROFINET IO controller and route from Ethernet to PROFINET.

The orange (solid) link is the engineering channel. The blue (dashed) link is the drive fieldbus. The green (dotted) curve is the logical routing tunnel: STARTER opens a PG function on the CPU, which in turn opens a PG/OP connection to the drive using the drive's configured PROFIBUS address. Once the tunnel is established, the drive's parameters, diagnostics, trace, and control panel become accessible to STARTER as if the PC were directly on PROFIBUS.

Prerequisites: Software, Licensing, and Hardware

Routing through an S7-300 MPI link requires the following engineering environment. Confirm every entry before starting the configuration; missing prerequisites account for the majority of "still not online" complaints.

PG/PC Interface Configuration

Routing begins on the engineering PC with the correct PG/PC interface assignment. The PC must publish itself to STARTER and STEP 7 as an S7 client on the MPI subnet, not as a direct bus participant on the drive's PROFIBUS. The PC Adapter (MPI) or the Ethernet interface is selected through the S7ONLINE access point.

1. Open Control Panel → Siemens Automation → Set PG/PC Interface (the applet is installed by STEP 7 / Drive ES).
2. Set the Access Point of the Application to S7ONLINE.
3. Set the Interface Parameter Assignment Used to PC Adapter (MPI) for an MPI PC adapter or to TCP/IP -> ISO -> Ethernet for an Ethernet link to a PN/DP CPU.
4. Open Properties on the selected interface and set the following:

Drive Placement in HW Config

Routing depends on the drive being a slave device of the S7-300 CPU in the STEP 7 hardware configuration. The drive must be dragged from the HW catalog onto the CPU's DP master system line, not added as a peer station. The same rule applies to PROFINET: the drive is placed on the IO controller system of the PN port.

1. In SIMATIC Manager open the S7-300 station and double-click Hardware.
2. Open the catalog and navigate to PROFIBUS DP → SINAMICS → G120 (or the relevant drive family). If the device is missing, install the GSD file from Options → Install GSD first.
3. Drag the drive to the DP master system line of the CPU's DP port.
4. Set the drive's PROFIBUS address. This must match the address selected on the Control Unit's DIP switches (or parameter p0918 on firmware V4.7+ where DIP switches are off).
5. Double-click the drive to open its properties and confirm the diagnostic and process data slots are configured. For most G120 applications, the Standard telegram 1 (PZD 2/2) is sufficient for cyclic data; the DP-V1 class 2 connection used by STARTER is established automatically once the device is in the project.
6. Save and compile the HW configuration, then download it to the CPU.

STARTER Online Configuration and Bus ID

Once the drive is a child of the CPU in HW Config, STARTER uses the S7 routing function. The bus ID parameter in the Accessible Nodes dialog tells STARTER which downstream subnet of the S7 project tree to scan. The MPI subnet is always ID 0. The first DP master system attached to the CPU is ID 1, the second is ID 2, and so on. The first PROFINET IO system is also typically ID 1, but its index in the routing list depends on the order the subnets were added in STEP 7.

1. Open STARTER and load the project that contains the drive.
2. Right-click the drive in the project tree and choose Online → Accessible Nodes (or Online → Target system → PC/PG).
3. In the Accessible Nodes dialog, set the PG/PC Interface to S7ONLINE and the Bus ID to the PROFIBUS subnet that holds the drive (typically 1). For PROFINET use the IO system bus ID.
4. Click Display. STARTER enumerates reachable nodes on the selected bus by walking the routing path PC → MPI → CPU → DP master → drive.
5. Select the drive and click Apply. The drive is now online through the routing tunnel.

Step-by-Step Routing Configuration Procedure

The end-to-end procedure for establishing an online connection from STARTER to a drive through an S7-300 MPI link. Run the steps in order. Each step has a deterministic verification check.

1. Confirm physical bus topology. The PC Adapter is plugged into the S7-300 MPI port (X1 on the CPU). The PROFIBUS DP cable from the drive's X126 to the CPU's X2 (DP port) has bus termination active at both physical ends. Use a PROFIBUS terminator on the drive if it is the last device on the segment.
2. Confirm MPI address and speed. In STEP 7, open HW Config, double-click the CPU's MPI port and read the configured Address (default 2) and Transmission Speed (default 187.5 kbit/s). Match these in the PC Adapter's properties dialog.
3. Place the drive under the CPU. In HW Config, drag the drive from the catalog onto the DP master system of the CPU. Assign the same PROFIBUS address as set on the drive (DIP switch or p0918). Save, compile, and download HW Config to the CPU. Verify with Station → Online → Online & Diagnostics; the drive should appear with a green check.
4. Assign the PG/PC interface to S7ONLINE. In Set PG/PC Interface, choose S7ONLINE as the access point and PC Adapter (MPI) as the parameter assignment. Test the bus via Diagnostics → Test; expect all visible MPI nodes to be listed.
5. Open STARTER and load the project. In STARTER, open the project that references the same drive under the same CPU. The drive's project node must show the same PROFIBUS address as the one configured in HW Config.
6. Set the online access point inside STARTER. In STARTER choose Tools → Set PG/PC Interface and confirm the same S7ONLINE / PC Adapter (MPI) assignment. The interface label inside STARTER must read S7ONLINE (PC Adapter (MPI)), not DRIVE (PROFIBUS) or DRIVE (Ethernet).
7. Open Accessible Nodes with the correct bus ID. Right-click the drive → Online → Accessible Nodes. Set the bus ID to the PROFIBUS subnet number (typically 1). Click Display. The drive must appear with its configured PROFIBUS address.
8. Connect to the target system. Select the drive in the list and click Apply. STARTER establishes the routing tunnel. The drive's online status indicator turns green.
9. Verify online access. Open the drive's expert list, the control panel, or the diagnostics buffer. Read a non-zero parameter (e.g. r0002 drive state) to confirm the connection is live.

Verification and Online Diagnostics

After the routing tunnel is established, the connection can be verified in three places: STEP 7 (online diagnostics of the CPU), STARTER (online parameter access on the drive), and the drive's own control panel and LED status. A connection is considered healthy only when all three confirm the online state.

PROFINET Routing Alternative

When the S7-300 CPU has an integrated PROFINET port (315-2 PN/DP, 317-2 PN/DP, 319-3 PN/DP) or an Ethernet CP (CP 343-1 Lean / Standard / Advanced), the same routing function works over PROFINET. The PG connects to the CPU over Ethernet, the drive sits on the PROFINET IO controller system, and STARTER routes through the CPU. The topology is functionally identical to the PROFIBUS case but operates at 100 Mbit/s, which reduces drive parameter upload time from minutes to seconds.

1. Connect the PC to the CPU's PROFINET port (X1 on a PN/DP CPU, X1 or X2 on a 317-2 PN/DP).
2. Set the PG/PC interface to TCP/IP -> ISO -> Ethernet with the CPU's IP address as the access point.
3. Place the drive under the PROFINET IO system in HW Config. Use the drive's GSDML file, not its GSD file.
4. In STARTER, the bus ID of the PROFINET IO system is typically 1 if it is the first IO system, regardless of whether MPI is configured.
5. Test the connection with STARTER's Accessible Nodes exactly as in the PROFIBUS case.

The PROFINET path is preferred for large parameter sets (firmware update, full parameter backup/restore) because the higher bandwidth makes the operation visibly faster. The MPI path remains useful for legacy hardware where the CPU has no Ethernet port and the existing PC Adapter is the only available engineering tool.

Troubleshooting Matrix

The following table maps the most common field-reported symptoms on the S7-300 MPI → drive topology to the underlying cause and the corrective action. Symptoms are listed in the order in which they are typically encountered during a first-time commissioning attempt.

Field-Commissioning Caveats and Best Practices

The following caveats are observed in repeated field deployments. Each is a concrete, testable condition, not a generic recommendation.

1. MPI is a low-bandwidth medium. At 187.5 kbit/s a full parameter upload from a G120 takes 4 – 8 minutes; a firmware update can take 30 – 60 minutes. For projects with multiple drives, switch to PROFINET routing or a direct PROFIBUS connection for the bulk transfer window.
2. MPI termination is on the CPU only. S7-300 MPI ports have built-in termination that is automatically enabled by STEP 7 when the CPU detects no other terminator. Do not add an external MPI terminator unless the bus is being extended through a repeater or OLM.
3. PC Adapter is not a passive tap. A PC Adapter USB A2 acts as a bus master. If the PG/PC is configured as "only master on the bus" and another master is present, bus contention can occur. Use the setting "PG/PC is the only master" only when no OP/TP or other CPU is connected to the MPI segment.
4. Routing consumes CPU resources. The S7-300 CPU dedicates a portion of its routing buffer to PG routing connections. A typical CPU 315-2 PN/DP supports 4 – 8 simultaneous routing connections depending on firmware version. Close STARTER and STEP 7 sessions when they are not in use to free routing resources for HMI or other PG/OP clients.
5. Drive ES licensing is not retroactive. If a project was created without Drive ES and the drive is configured as a peer station, adding Drive ES later does not migrate the existing project. Re-create the drive as a child of the CPU in STEP 7 instead.
6. Firmware alignment matters. STARTER's device library expects a specific range of drive firmware versions. A drive running V4.5 will not load a project created against V4.7. Match the firmware version, or upgrade the drive firmware before commissioning.
7. Save the offline project before going online. Routing an online read on top of an unsaved offline project can cause STARTER to overwrite the offline parameters with online values without warning. Save → then connect.
8. Use the online "Load to PG" command, not "Upload to PG". "Load to PG" is the safe read of the drive's current parameters; "Upload to PG" reads the drive's offline image. The two will diverge if the drive has been changed online without the project being updated.
9. Online access while the drive is in run is read-only by default. Parameter writes require the drive to be in "Commissioning" state, or require the safety password for safety-related parameters. Confirm the drive's r0002 state word before attempting a parameter download.
10. Keep a copy of the offline project on a network share. When STARTER is closed after a routing session, the in-memory drive image is lost. Without a saved offline project, the next engineer who connects to the drive starts from a blank project.

Related Documents and Manuals

The following Siemens publications support the procedure above. Use them to confirm parameters, telegram assignments, and version-specific behavior for the drive family in use.

• Siemens Support Entry 2383206 — How do you configure S7 routing for STARTER? — primary procedure reference for routing through S7-300 / S7-400.
• Siemens Support Entry 26202408 — STARTER commissioning tool manual — STARTER user interface, online mode, parameter access.
• Siemens Support Entry 109765471 — Drive ES Basic manual — Drive ES integration in STEP 7 / SIMATIC Manager.
• Siemens Support Entry 12996906 — S7-300 CPU 31x manual collection — CPU-specific routing and PG/OP connection limits.
• Siemens Support Entry 109751799 — SINAMICS G120 operating instructions — CU240E-2 PROFIBUS connection, address setting, status LEDs.

Frequently Asked Questions