Sinamics S110 Telegram 1 Communication: S7-315 PN Troubleshooting

Sinamics S110 Telegram 1 Communication Failure with S7-315-2 PN PLC: Process Image, Life Bit, and BICO

When a SINAMICS S110 with CU305 PN and a SIMATIC S7-315-2 PN/DP CPU are wired via PROFINET and configured for Standard Telegram 1, PZD-2/2, a very common symptom is that the PLC writes the control word to QW256 (or PQW256) but STARTER's online monitor shows STW1 holding at 0x0000. The status word at IW256 (or PIW256) never updates. The drive runs from the STARTER control panel because that path is independent of the PROFIdrive telegram; it does not validate the bus path. PROFINET shows no diagnostic interrupt because the I/O slot is connected at the slot level, but the application-layer handshake has not been completed end-to-end by the user program. Four layered defects produce this signature: (1) addressing outside the S7-300 process image partition, (2) missing life bit in STW1, (3) PROFINET device name not yet bound through SIMATIC Manager, and (4) wrong byte order on the cyclic word. Each must be cleared before the cyclic channel is usable.

1. Affected Hardware, Firmware, and Software

Reference: SINAMICS S110 List Manual, S7-300 CPU 315-2 PN/DP Manual, STARTER commissioning tool.

2. System Topology

3. Root Cause Decomposition

Four independent faults can mask the Telegram 1 exchange. Each must be cleared before the cyclic channel is usable; clearing only one will leave the symptom visible.

3.1 Process image boundary (PIW / PQW vs IW / QW)

The S7-300 default process image partition ends at IW/PQW 255 in many configurations of CPU 315-2 PN/DP. Address 256 lies outside the default partition; STEP 7 will raise a peripheral access error at runtime when the user program reads IW256 or writes QW256. The drive itself is unaffected (PROFINET continues to indicate no fault) and STARTER displays 0 because the PLC never actually wrote the slot, or because the write was masked by an OB error. Use PIW 256/PQW 256 for direct peripheral access, or extend the process image in HW Config.

3.2 Missing master control / life bit (STW1 bit 10)

For Standard Telegram 1 on SINAMICS S110, the drive only honors the PROFIdrive control word when bit 10 (master control by PLC) is set continuously. If the user code writes 0x047E and forgets bit 10, or writes a plain ON sequence like 0x000F, the drive drops the control word internally and STARTER shows 0000. Bit 10 must be latched on for the duration of PLC-driven operation; the PLC should refresh it every cycle. The drive applies a sign-of-life check on bit 10 and on a 4-bit toggling counter in bit 12–15 for some telegrams; even on Telegram 1, however, the explicit master control bit 10 is the gating condition for PLC command acceptance.

3.3 PROFINET device name not bound

Cyclic PROFINET IO requires the IO device to carry the same PROFINET name configured in HW Config. The drive may be reachable in the topology view without alarms, but if the device name is blank or still carries the factory default, the I/O slot is not associated with the configured slot and cyclic PZD exchange is suppressed. STARTER still reports the drive online because STARTER uses its own TCP-based routing (port 50000 / 50001 with the S110 routing protocol) independent of the PROFINET name. This is why the motor runs from STARTER's control panel while the PLC appears to have no influence.

3.4 Endian / byte order mismatch

PROFIdrive is little-endian on the wire. If the user's FC writes a Big-Endian constant (e.g. writes 0x7E04 instead of 0x047E), the drive receives 0x7E04 in PZD1; STARTER reflects that value rather than the expected 0x047E. The signal is on the wire but the meaning is wrong. STEP 7 S7-300 STL and LAD both treat W#16#047E as little-endian, but some HMI tag drivers and some user-conversion blocks may pad or swap the byte order; always write the constant in native S7 word order and verify in STARTER before assuming the wire path is correct.

4. Telegram 1 PZD-2/2 Process Data Layout

5. Control Word STW1 Bit Definitions

6. Status Word ZSW1 Bit Definitions

7. Speed Setpoint Encoding

The S110 scales the setpoint via the reference speed parameter p2000 (RPM). The PLC must send a 16-bit signed word where 0x4000 = 16384 decimal = 100% of p2000. Negative directions are supported with two's-complement encoding: 0xC000 = -16384 = -100% of p2000. For example, if p2000 = 3000 RPM, then 0x4000 ⇒ 3000 RPM and 0x2000 ⇒ 1500 RPM. Read or write p2000 in STARTER under Drive → Setpoint channel → Speed setpoint, or via the parameter list view. Verify with the formula N_command = NSOLL × p2000 / 16384. Compare against r0063[0] (setpoint after RFG) and r0021 (actual smoothed) in STARTER's trace to confirm the wire value is reaching the controller.

8. Procedure: Extend the S7-300 Process Image

Choose one of two approaches depending on whether the offset is reserved for one drive or will be used by many I/O modules.

Option A — Direct peripheral access (preferred for one-off drives)

1. Open SIMATIC Manager and load the S7-300 station.
2. Open the FC/FB that drives the Telegram 1 exchange.
3. Replace every IW 256 with PIW 256 and every QW 256 with PQW 256; apply the same substitution at offset 258.
4. Recompile, download the program, and put the CPU in RUN.
5. PIW/PQW reads the most recent process image value of the slot on the peripheral bus and bypasses the S7-300 input/output image table. Consistency across the entire 4-word area is not guaranteed with peripheral access; for Telegram 1 (2 receive + 2 transmit words) this is acceptable because each word is self-consistent.

Option B — Extend the process image partition (preferred for permanent installations)

1. In SIMATIC Manager, open HW Config on the S7-300 station.
2. Double-click the CPU 315-2 PN/DP entry.
3. Select the "Cycle/Clock Memory" tab.
4. Set "Size of the process image input" and "Size of the process image output" to cover at least 0..259. A typical value is 256 (default) extended to 512 (covers 0..511).
5. Save, compile, and download HW Config to the PLC.
6. Update the user program to use the standard I/Q area: IW 256/QW 256 and IW 258/QW 258.
7. Re-verify cyclic update on the online Monitor/Modify view of the I/Q words.

9. Procedure: Build the Control Word Sequence

1. Pre-load 0x047E into PQW 256 and hold it for at least one PROFINET cycle. Decoding: 0000_0100_0111_1110 sets bits 1, 2, 3, 4, 5, 6, 10. Bits 1 and 2 are low-active so they are de-asserted (OFF2 inactive, OFF3 inactive). Bit 3 enables the inverter; bit 4 enables the RFG; bit 5 freezes/unfreezes the RFG; bit 6 enables the setpoint; bit 10 asserts master control by PLC.
2. Once the drive reports ZSW1 bit 0 = 1 (Ready to switch on), bit 1 = 1 (Ready to operate), and bit 5 = 1 (OFF3 inactive) at PIW 256, write 0x047F to PQW 256. This adds bit 0 (ON/OFF1). The drive will close the main contactor, fire the pulses, and follow the setpoint at PQW 258.
3. If a fault occurs (ZSW1 bit 3 = 1), wait for ZSW1 bit 1 = 0 (Ready to operate drops), then raise STW1 bit 7 from 0 → 1 to acknowledge. Maintain bit 7 high for at least one cycle, then drop it. The S110 requires bit 7 to fall again before the next acknowledge attempt — repeated edge attempts without the falling edge are ignored.
4. For controlled stop, drop bit 0 (write 0x047E) and let the RFG ramp down to zero. To coast stop, drop bits 1 and 3 (write 0x0438 = OFF2 and inverter inhibit, master control still held). For fast stop, drop bit 2 (write 0x047A).
5. Sample STL snippet for OB1:
   L 0x047E
T PQW 256
L 0x4000
T PQW 258
L PIW 256
T MW 100
L PIW 258
T MW 102

10. Procedure: Assign the PROFINET Device Name

1. Connect STARTER online with the S110 CU305 PN.
2. Confirm the IP and PROFINET name are blank or factory-default on the device (visible under Communication → PROFINET interface in STARTER, or in the diagnostic buffer). Factory name is typically s110-cu305pn or empty.
3. In SIMATIC Manager HW Config, right-click the S110 device entry and choose PLC → Ethernet → Assign Device Name.
4. Select the target IO device by MAC address or by scanning the accessible nodes, enter the configured name (must match the HW Config device entry), and click Assign Name.
5. Wait for the assignment to complete and the device to restart the PROFINET stack. The "blue check mark" in HW Config indicates the device name matches the configured slot; this is necessary but not sufficient for cyclic data because the cyclic data path is set up by the connection in HW Config, which happens at PLC startup.
6. Power-cycle the PLC, restart the cyclic exchange, and check STARTER's control word display. The S110 should now accept writes from PQW 256.

11. Procedure: Verify Byte Order and Diagnose

1. In STARTER, open the Control/Status words online view for the Drive_1 DO.
2. In the PLC, force PQW 256 = W#16#047E and PQW 258 = W#16#4000 (50% speed if p2000 = 3000 RPM).
3. Observe STARTER's STW1 display. If it shows 0x047E, the byte order is correct. If it shows 0x7E04, the S7-300 is writing Big-Endian and the swap must be reversed in the user code (use CAW or rebuild the constant).
4. Observe NIST at PIW 258. The drive should echo the speed setpoint at startup (NIST near 0 RPM) then climb toward the setpoint at PQW 258 = 0x4000 with STW1 = 0x047F.
5. Read PIW 256 to verify ZSW1. Bit 0 and bit 1 should rise as the drive progresses through the switch-on sequence.
6. Cross-check using a STARTER trace of r0063 (setpoint after RFG) vs r0021 (actual smoothed) to confirm the speed chain is closed.

12. Relevant SINAMICS S110 Parameters

13. Extended Troubleshooting Matrix

14. Verification Checklist

• PLC writes 0x047E to PQW 256; STARTER shows STW1 = 0x047E.
• PLC writes 0x047F to PQW 256; STARTER shows STW1 = 0x047F.
• PIW 256 reports ZSW1 with bit 0 = 1, bit 1 = 1, bit 2 = 1 after switch-on sequence.
• PQW 258 set to 0x4000 ⇒ PIW 258 reports NIST proportional to p2000 × 0.5 after ramp.
• No F07801 / F07802 (PROFINET link loss) entries in the SINAMICS diagnostic buffer.
• PROFINET device name on drive matches HW Config name.
• HW Config shows blue check mark for both Drive_1 and Control_Unit entries.
• Cyclic time per p0922 telegram is ≤ bus update time configured in PROFINET IO properties.
• STARTER online trace shows STW1 bit 10 toggling on every PLC cycle without drop-outs.
• r0021 actual speed matches r0063 setpoint after ramp completion at nominal NSOLL.
• Stop sequence: drop STW1 bit 0 → motor decelerates per p1121 → ZSW1 bit 2 clears → ZSW1 bit 1 still 1 → bit 0 still 1.
• Fault acknowledge: trigger STW1 bit 7 rising edge → fault clears within 2 cycles → ZSW1 bit 3 falls.

15. Frequently Asked Questions