Assigning PROFIBUS Addresses to SINAMICS G120 via S7-300 S7 Routing

This technical reference documents the complete procedure for assigning PROFIBUS node addresses to SINAMICS G120 frequency converters wired to a SIMATIC S7-300 CPU (specifically the S7-315-2 PN/DP) when the engineering station is connected only via Ethernet to the PLC's PROFINET interface. The procedure resolves the classic "You have not made any PROFIBUS interface parameter assignment to the access point S7ONLINE" error that surfaces when an engineer tries to reach the G120 from HW Config → PLC → PROFIBUS → Assign PROFIBUS Address without first binding the PG/PC interface to the PROFINET side of the CPU. The recommended approach uses S7 routing through the CPU as a gateway and is fully supported on S7-315-2 PN/DP firmware V3.1 or later. For background on Siemens' online / routing concept across SIMATIC controllers, refer to the official Siemens Support FAQ How do I go online? (PDF).

1. System Topology and Component Roles

The reference architecture consists of three logical segments joined by an S7-300 CPU acting as a routing gateway. Understanding the topology is essential because the STEP 7 error message is a direct symptom of the routing boundary, not a fault on the drive or on the PG/PC interface itself.

Engineering station. The Field PG has only an Ethernet / PROFINET connection to the CPU's PN port. The PG/PC interface access point is set to S7ONLINE, which is the default access point used by both STEP 7 and STARTER for online operations.

S7-300 CPU as router. The S7-315-2 PN/DP terminates the PROFINET connection from the PG on its X1 port and operates the integrated PROFIBUS DP master on its X2 port, to which the G120 drives are physically wired. From firmware V3.1 onward, the CPU supports both S7 routing and dataset routing between the PROFINET and PROFIBUS sides. Earlier firmware versions support S7 routing only with limitations; firmware older than V3.0 generally does not support the PN→DP routing path required for this procedure.

SINAMICS G120 drive segment. Each drive pairs a Control Unit with a Power Module. The Control Unit exposes a 9-pin Sub-D PROFIBUS connector and joins the DP segment at a node address between 1 and 126. Address 0 is reserved for the master class 2 (typically a PG); address 127 is the PROFIBUS broadcast address and must not be assigned to operational drives. Out of the box, a factory-fresh G120 Control Unit ships with the address switches set to 0,0, which means the value stored in parameter p0918 is used (default p0918 = 126); if a drive appears "unresponsive" at commissioning, it is often sitting on address 126 because the engineer never adjusted the switches or parameter.

2. Why the S7ONLINE Parameter Assignment Error Appears

The error text reported by STEP 7 — "you have not made any PROFIBUS interface parameter assignment to the access point S7ONLINE. Call up the Set PG/PC Interface to do this" — does not mean the G120 is at fault. It means STEP 7 attempted to enumerate the PROFIBUS interfaces available to the access point S7ONLINE and found none bound to it.

The S7ONLINE access point is a symbolic alias that maps to a concrete protocol stack and physical interface. On a PG that has both an Ethernet adapter and a CP 5611 / CP 5612 / CP 5512 PROFIBUS card, two bindings of S7ONLINE are possible:

• S7ONLINE → TCP/IP (RFC1006). Uses the PC's standard Ethernet adapter; the only viable path when the PG has no PROFIBUS hardware installed and is connected solely over Ethernet to the CPU's PN port.
• S7ONLINE → ISO (or ISO Ind. Ethernet). Uses an ISO-over-Ethernet CP or, on a PROFIBUS CP, an MPI/DP protocol stack with a separate PROFIBUS segment.

When the user enters HW Config → PLC → PROFIBUS → Assign PROFIBUS Address, STEP 7 first checks the S7ONLINE binding. If the binding points to a PROFIBUS CP that is not present, or to no interface at all (i.e., S7ONLINE is unbound or points to a CP whose driver is unloaded), STEP 7 cannot establish a PROFIBUS connection to the drive and emits the error above. The actual PROFIBUS nodes are physically reachable only through the S7-300 CPU's DP master, but STEP 7 does not know the user intends to use the PN port plus S7 routing unless S7ONLINE is correctly bound to the Ethernet adapter and the routing tables in the CPU are configured.

Resolving the error therefore has two independent prongs:

1. Bind S7ONLINE to the Ethernet adapter that is physically connected to the CPU's PN port, using the Set PG/PC Interface dialog.
2. Configure the S7-300 CPU as a router between the PROFINET and PROFIBUS subnets in HW Config, so STEP 7 can compute an S7 routing path to the drive.

3. Prerequisites

4. PG/PC Interface Configuration (Resolving the Error)

Open Set PG/PC Interface from Start → SIMATIC → STEP 7 → Set PG/PC Interface (or Control Panel → Set PG/PC Interface on older Windows versions). The dialog lists every installed interface and its current access-point assignment.

1. Select the Ethernet adapter physically connected to the CPU's PN port. The entry is typically labeled TCP/IP (RFC1006) → <network adapter name>.
2. Click Set as default for S7ONLINE (or use the access-point drop-down to set S7ONLINE to TCP/IP explicitly).
3. Confirm with OK. The diagnostic icon must turn green and read "Active".
4. Open a command prompt and verify reachability: ping 192.168.0.1 (or the actual CPU IP). The reply must be < 1 ms on a back-to-back connection.
5. In SIMATIC Manager, open Options → PG/PC Interface and confirm that S7ONLINE → TCP/IP → <adapter> is selected.

5. S7 Routing Fundamentals for S7-315-2 PN/DP

S7 routing is a Siemens-proprietary mechanism that allows an S7 communication relationship initiated by a PG on one subnet to be transparently forwarded by a CPU to a node on a different subnet. For the S7-315-2 PN/DP, the CPU maintains a routing table inside its system data that lists every interface, the MAC address range of that interface's subnet, and the next-hop bridge for off-subnet destinations. The Siemens support document FAQ — How do I go online? explicitly notes that any SIMATIC control supporting the S7 routing function between all interfaces allows the PG to connect to any interface (e.g., X150, PROFINET, or Ethernet), which is the exact behavior we exploit here on the PN port of the S7-315-2 PN/DP.

Routing is enabled by default on S7-300 PN/DP CPUs as long as the subnet properties are correctly configured in HW Config. Two conditions must be met:

• The CPU's PROFINET interface must belong to an Ethernet subnet in HW Config (the Properties → Interface dialog of the PN port), and that subnet must be the one the PG is on.
• The CPU's PROFIBUS interface must belong to a PROFIBUS subnet in HW Config, and that subnet must contain the G120 nodes (either as configured DP slaves or as accessible nodes via Assign PROFIBUS Address).

When both subnets are configured, STEP 7 automatically populates the CPU's routing table on download, and the CPU forwards S7 communication packets between the two subnets. The transparent routing is also called "S7 routing"; it uses TSAP-based ISO transport (default TSAP 01.01 for PG connections) and does not require any project-side change beyond having the subnets declared.

6. Assigning the PROFIBUS Node Address via S7 Routing

With S7ONLINE correctly bound and the CPU's routing table populated, the drive segment becomes reachable from STEP 7 even though no PROFIBUS interface exists on the PG. Use the following procedure to assign the address.

1. Open HW Config for the S7 station. Confirm the CPU is online (green check next to the slot).
2. Open the PROFIBUS subnet attached to the CPU's DP master (X2). The subnet must be named (for example PROFIBUS_1) and have the correct baud rate (typically 1.5 Mbit/s or 12 Mbit/s for short segments).
3. Right-click the PROFIBUS line and select Assign PROFIBUS Address…. The dialog displays the assigned nodes found on the segment.
4. STEP 7 now performs an S7 routing call through the CPU and enumerates the PROFIBUS DP slaves present on the segment. Devices that have not yet been assigned an address appear with a "—" in the address column. If a drive is listed but not addressable, double-check 24 V, bus terminator, and address switch position (Section 7).
5. Select the G120 with the unknown address and click Assign Address. Enter the desired DP address (e.g., 4 for the first drive, then 5, 6, …). Confirm with OK.
6. STEP 7 downloads the address via the routing path. The G120 Control Unit accepts the new address and stores it in parameter p0918 on its next power-up. If the address switches on the CU are at 0,0, the parameter value takes effect; if the switches are non-zero, the switch position overrides p0918 at every power-up.

7. Alternative: PROFIBUS Address Switches on the G120 Control Unit

The SINAMICS G120 Control Unit is shipped with two rotary address switches on its front panel. On the CU240B-2 DP and CU240E-2 DP variants, the switches are clearly labeled on the housing; on the CU250S-2 DP variant the same convention applies. The two switches represent the high digit (tens) and the low digit (ones) of the PROFIBUS address in base 10, giving a range of 1 – 126. Positions 0,0 and 1,2,7 (i.e., 127) are reserved.

Procedure for switch-based addressing:

1. Power off the G120 Control Unit (24 V supply removed).
2. Using a small flat-blade screwdriver, set the two rotary switches to the desired address (e.g., 0 × 4 for address 4, 1 × 2 for address 12).
3. Re-apply 24 V. The Control Unit reads the switch position during boot and joins the bus at that address. The previous value of p0918 is retained in memory but ignored until the switches are returned to 0,0.
4. From STEP 7, run HW Config → PROFIBUS → Assign PROFIBUS Address and confirm the drive is now visible at the new address.

8. STARTER Configuration for Online Parameter Access

Once the G120 has a valid PROFIBUS address, the next step in most commissioning flows is to load the drive parameters (motor data, ramp times, control words) via STARTER. STARTER must be configured to route through the same S7 path used for address assignment.

1. In STARTER, open Project → Accessible nodes or click the Connect to target system button on the toolbar.
2. STARTER uses the S7ONLINE access point. Confirm in Options → Set PG/PC Interface that S7ONLINE is bound to the Ethernet adapter (same as STEP 7).
3. STARTER enumerates the stations reachable through S7 routing. Expand the S7-300 → PROFIBUS tree to see the G120 nodes.
4. Select the G120 with the desired address and click Connect to target system. STARTER performs an S7 routing call to the drive.
5. Open the configuration tree for the drive. Read the parameters (online → offline upload) or download the offline configuration (offline → online download). Pay particular attention to:

• p0010 — commissioning parameter filter; set to 1 for quick commissioning, 30 for factory reset, 0 for normal operation.
• p0100 — motor standard (0 = IEC, 1 = NEMA).
• p0201 — power module code number; should match the PM in use.
• p0300 — motor type selection.
• p0304 / p0305 — motor rated voltage / current.
• p0918 — PROFIBUS node address (read-only if hardware switches are non-zero).
• p0922 — PROFIBUS PZD telegram selection (e.g., 1 = Standard Telegram 1, 20 = SIEMENS Telegram 20).
• p2051 — PZD send-word mapping for each word.
• p1070 — main setpoint source; for PLC control, set to the fieldbus setpoint connector (e.g., r2050.0).

6. After parameter download, perform Copy RAM to ROM (or p0971 = 1) so the configuration survives a power cycle.

For TIA Portal projects, the same logic applies via Startdrive V15.1 or later. The official TIA Portal configuration guide for the SINAMICS G120 is published at Configuring SINAMICS G120 — TIA Portal Documentation.

9. Dataset Routing vs S7 Routing — When to Use Each

Engineers often confuse the two routing mechanisms because the STEP 7 / STARTER user interface does not distinguish them prominently. The decision matrix below clarifies the boundary.

Dataset routing uses record (dataset) read/write commands that the proxy translates into PROFIBUS DP-V1 read/write services. It is required only when the G120 is on a PROFIBUS sub-segment behind a PROFINET proxy that does not have its own S7 routing table. For the topology in Section 1 (CPU → G120 over DP), S7 routing is sufficient.

10. Verification and Acceptance Test

After address assignment and parameter download, perform the following checks to confirm the routing path is functional and the drive is correctly configured.

1. Online visibility. In HW Config, the G120 appears as a configured DP slave on the PROFIBUS subnet. Its online status icon shows a green check. No yellow triangle (configuration mismatch) should be present.
2. Diagnostic buffer. Open the CPU's online diagnostic buffer. Look for entries of type "PROFIBUS station failure / return" corresponding to the drive's address. A clean return event confirms the drive joined the bus correctly.
3. STARTER online. From STARTER, connect to the drive. The Online tab should display live parameter values (e.g., r0002 = drive status word, r0021 = actual speed, r0026 = DC link voltage).
4. Control test. From STARTER, take the drive into the "Control Panel" (commissioning control panel) and issue a small setpoint (e.g., 5 % speed). Verify the motor spins and the ramp time matches the configured value (p1120 / p1121). Disable the control panel before leaving commissioning.
5. Cold-start repeatability. Power-cycle the G120 Control Unit. After re-boot, confirm the drive is reachable at the same address and STARTER can connect without re-assigning p0918.
6. Routing continuity. Open the CPU's online routing table via PLC → Diagnostics → Routing. The PN and DP subnets should both be listed with the correct interface MACs.

11. Troubleshooting Matrix

12. Frequently Asked Questions