Resolving ET 200M PA Link Communication with CPU 315-2 PN/DP

Resolving ET 200M PA Link Communication with CPU 315-2 PN/DP

This technical reference covers a recurring commissioning problem when wiring a Proline Promass 83 PA Coriolis flowmeter through an ET 200M PA Link (IM 153-2 + FDC 157-0) to a Siemens SIMATIC S7-300 CPU 315-2 PN/DP. Two sequential symptoms are addressed: (1) the IM 153-2 reports "not connected" in the CPU diagnostic buffer because the physical PROFIBUS address disagrees with HW Config, and (2) PROFIBUS-PA feedback is absent because the PA segment termination is missing or the Promass 83 GSD has not been mapped into the slot model.

1. System Architecture Overview

The chain between the S7 CPU and the field device is layered. Each layer must be configured independently; a defect at any layer blocks all upstream communication.

2. Hardware Components and Order Numbers

3. Symptom 1 — "IM 153-2 Not Connected" Diagnostic Buffer Entry

3.1 Failure Signature

After STEP 7 HW Config is downloaded, the CPU diagnostic buffer emits an entry similar to:

Event ID   : 0x39E2
Description: Distributed I/O: Station failure
Slave addr : 3
Module     : IM 153-2 (6ES7153-2BA10-0XB0)
Comment    : Station failure - DP slave not reachable

Online view in HW Config shows the IM 153-2 with a red cross; cyclic I/O exchange never starts. The most common cause in field reports is a mismatch between the rotary / DIP address on the physical IM 153-2 and the PROFIBUS address entered in HW Config. The IM 153-2 has no rotary encoder like the IM 151; the address is set exclusively with the front-panel DIP switches (S1, 8-pole) on older revisions or with the rotary selector on newer (-2BA70) revisions.

3.2 IM 153-2 DIP Switch Mapping

Switch ON = logic 1 (closed toward the corresponding binary weight). Address 0 is reserved for DP masters and must not be assigned to the IM 153-2. Maximum legal DP slave address is 125 (0x7D). The setting is read only at power-up; a hot change is ignored. Always cycle power after changing the address.

3.3 HW Config Entry That Must Match

In SIMATIC Manager open the project, double-click the DP master system on the CPU, insert the IM 153-2 at the exact address used by the DIP switches, and accept the GSD file revision that matches the installed firmware. The PROFIBUS GSD for the IM 153-2 is SIEM802D.GSD for legacy IM 153-2 heads and SIEM815F.GSD for the high-feature revision (-2BA70). The GSD revision is printed on the device label.

4. Symptom 2 — PA Segment Returns No Process Data

4.1 Failure Signature

The DP layer comes up green (IM 153-2 reachable, no SF on the head module), but the PA slave "Promass 83" shows:

• Slot diagnosis byte 0x00 — slave does not respond.
• SF LED on FDC 157-0 lit steady red.
• No cyclic input data on the configured PA slave slot.

4.2 PA Bus Termination — The Most Common Cause

PROFIBUS-PA operates on IEC 61158-2 Manchester-Bus-Powered (MBP) signalling at 31.25 kbit/s. The segment is a single linear bus terminated at both physical ends with a defined characteristic impedance of 100 Ω ± 20 % in series with 1 µF. Without termination the signal reflections corrupt every telegram and the slave never synchronises.

Unlike PROFIBUS-DP, the termination resistor for PA cannot be a passive 220 Ω across the two wires — that is the DP practice. For PA, the terminator is the active PA segment terminator (a power-rail-mounted unit, e.g. 6ES7157-0AC83 accessory module, or a third-party MBP terminator such as Phoenix Contact FLT-PAIS or Relcom FPT-2). It must be connected at the physically most distant point of the segment, after the last PA device.

4.3 Why the Terminator Must Be Active

An active MBP terminator fulfils three functions a passive resistor cannot:

1. Provides a defined reference voltage so the slaves can be bus-powered.
2. Suppresses reflections with the precise 100 Ω + 1 µF RC network.
3. Bleeds the segment to a safe potential when the coupler is unpowered, preventing field-device corruption.

4.4 FDC 157-0 Switch Settings

Enable S2 = ON on the FDC 157-0 if it sits at the near end of the PA segment. Then place the active terminator at the far end. Never enable two internal terminators and one external — that is three terminators and the segment will not initialise.

5. STEP 7 HW Config Procedure

5.1 Insert the PA Link

1. Open SIMATIC Manager → open the project → double-click Hardware.
2. On the CPU 315-2 PN/DP, double-click the DP interface row to open DP Master System Properties.
3. Drag the IM 153-2 (under PROFIBUS-DP > ET 200M) onto the DP master system line at the address matching the physical DIP setting.
4. Open the IM 153-2 station by double-clicking the inserted icon.
5. Insert the FDC 157-0 in slot 4 of the virtual ET 200M rack (slots 1–3 are reserved by the IM 153-2).
6. Drag the Promass 83 PA from the device catalogue (you must first install the E+H GSD file via Options > Install GSD File) onto the PA master system line that appears under the FDC 157-0.

5.2 Slot Configuration of Promass 83

After installing the E+H GSD for the Promass 83 PB/PA profile, the device exposes a multi-slot modular model. Typical mapping:

Refer to the official Proline Promass 83 Description of Device Functions and Operating Instructions for the exact slot map of your firmware revision (BA-prefixed manuals from Endress+Hauser).

5.3 PA Address Setting on Promass 83

Set the PA slave address in the Promass 83 local display under Setup > Communication > PROFIBUS-PA address, or via the on-device DIP switch on the display board. Default factory address is 126 (0x7E), which is the service address reserved for commissioning — change it to a free address between 3 and 124 (avoid 0, 1, 2 reserved for masters; avoid 126 which is the service address). The address must match the slot where the GSD icon was placed.

6. Diagnostic Buffer Interpretation

To export the diagnostic buffer cleanly, open CPU > Diagnostic Buffer, right-click in the event list, and select Save As Text. This produces a copyable file that can be attached to support requests without screenshots.

7. Cable Plant, Shielding, and EMC

8. Verification Procedure

1. Open HW Config and download the configuration to the CPU.
2. Open Online > Accessible Nodes; the IM 153-2 must appear at the configured address.
3. Open the diagnostic buffer — confirm no new Station failure entries.
4. Open Monitor/Modify on the PA slave slot; the Promass 83 process values (Mass Flow, Density, Temperature) must show live updates.
5. Toggle the slave address using the Promass 83 local display to verify two-way integrity.
6. Force a PA segment break by unplugging the last device and confirm the diagnostic buffer raises PA segment voltage fault — proves the coupler is supervising the segment.

9. Common Pitfalls and Field Tips

• Address set in hardware, configured in software — both must match exactly; verify by reading the IM 153-2 sticker and re-checking after every wiring change.
• Confusing DP termination with PA termination — a 220 Ω passive resistor on a PA segment will silence the segment. Use only active MBP terminators.
• Promass 83 factory address 126 — change it before the master polls; 126 is a service address not used in normal cyclic traffic.
• GSD file version mismatch — the Promass 83 has several firmware revisions; each maps to a different GSD. If HW Config refuses the device, install the matching GSD from E+H support.
• Cyclical power — IM 153-2 reads its address only at power-up. Cycling power is mandatory after every DIP change.
• FDC 157-0 slot — must be in slot 4 or higher of the ET 200M rack; slots 1–3 are reserved for the head module and any redundant pair.
• Diagnostic buffer access — always Save As Text the buffer so the events are searchable by Event ID.

10. Quick Reference — Parameter Table

11. FAQ