SITRANS MAG 6000 'Configuration Mismatch' Behind Y-Link S7-400H

Problem Statement and Field Symptoms

A SITRANS FM MAG 6000 electromagnetic flow transmitter is mounted on a Profibus DP segment that is electrically isolated from the higher-level controller by a Y-Link. The higher-level controller is a redundant SIMATIC S7-400H with the standard SIMATIC Profibus DP interface. When the commissioning engineer attempts to go online with the MAG 6000 from the S7-400H HW Config, the STEP 7 online view returns the diagnostic text "Configuration does not match the slave" (German: "Konfiguration stimmt nicht mit dem Slave überein"). The error appears under the following operating conditions:

• Bus termination is verified correct at both ends of the DP segment.
• Wiring and shielding conform to the Profibus cable spec.
• The MAG 6000 is visible from the PG in Profibus Diagnostics and responds to the bus address scan.
• The local MAG 6000 display shows valid flow readings.
• The GSD file si018129.gsd (Profile 3) is installed in STEP 7, and Profile 2 has also been tried with the same negative result.
• MAG 6000 main firmware: 3.03, Profibus module firmware: 2.01 rev C, ID Number: 8192 (0x2000).

Because the device is reachable on the wire but refuses the cyclic data exchange, the failure is not in layer 1 or layer 2. The defect sits in the configuration handshake between the DP master and the MAG 6000 DP slave. Y-Link is a known constraint in this handshake and is the prime suspect in the present case.

System Architecture and Component Identification

The segment under commissioning is a typical safety-oriented Profibus DP sub-network behind a Y-Link, used so that a single Profibus DP failure on the field side cannot propagate into the S7-400H backplane bus. The exact components reported in the field case are listed in the table below.

The network topology is shown in the SVG diagram below. Note the asymmetrical role of the Y-Link: from the higher-level master it looks like one DP slave with a fixed slot table, while from the lower-level field devices it is a DP master with its own set of allowed slaves and profiles.

Root Cause: GSD Profile and DPV1 Across a Y-Link

The "configuration does not match the slave" diagnostic is the DP slave's response to a Chk_Cfg telegram whose expected slot structure does not match the physical module selection it had reported in Diag_Data. The mismatch can be in any of:

• Number of input or output bytes per slot.
• Consistency setting (total length, unit, or both).
• Module identifier length field.
• Whether DPV1Enable = 1 is set on the master and whether the slave advertises DPV1 features in its GSD.
• Whether the Check_Ident_Number (PRM bit) is set and the value of the ID Number registered against the device family.

For the SITRANS FM MAG 6000 with Profibus module, the GSD file si018129.gsd declares Profile 3, which is the Profibus PA profile 3.0 condensed status and diagnostic model with DPV1 alarm and status slots. Behind a Y-Link, the higher-level master cannot tunnel DPV1 alarms from the field side without explicit slot configuration. The default slot table that STEP 7 inserts from the GSD for Profile 3 places an extended diagnostic slot and an alarm slot that the Y-Link does not pass through. The slave therefore rejects Chk_Cfg and the master reports the configuration mismatch.

Profile 2 is the classic Profibus PA profile 2.0 that uses only DPV0 cyclic I/O. The slot table for Profile 2 contains one or two input modules and one output module, with no DPV1 alarm or extended status slot. This profile passes through a Y-Link unchanged, which is why it works where Profile 3 does not.

The field report confirms exactly this behavior: the engineer tried both profiles and only Profile 2 should be expected to bring the device online. The historical observation from another integrator that "profile 2 works, profile 3 doesn't behind Y-Link" is consistent with the documented Y-Link behavior, not a defect of the MAG 6000.

GSD File Selection and Profile Mapping

Siemens ships a family of GSD files for the MAG 6000 Profibus module. The choice is driven by the desired profile and by the firmware installed in the field device. The mapping between installed firmware and the GSD files that are known to match is given in the table below. Always cross-check the GSD Revision field inside the GSD text with the device's hardware and firmware version before importing.

The exact GSD revision name is not always the one quoted in the field; the directory listing of the GSD package reveals the current one. The version of si018129 cited in the report is correct for Profile 3. For Profile 2, confirm that the GSD file ending in 28 or its successor is loaded.

Inside the GSD the relevant declarations are:

; --- Excerpt of a typical MAG 6000 GSD (Profile 2) ---
GSD_Revision          = 2
Vendor_Name           = "Siemens AG"
Model_Name            = "SITRANS FM MAG 6000"
Ident_Number          = 0x2000
Protocol_Ident        = 0
Station_Type          = 0
FMS_supp              = 0
Hardware_Release      = "2.0"
Software_Release      = "V2.01"

; Redundancy not supported
Redundancy            = 0

; DPV0 only on this profile
DPV1_Slave            = 0

; Cyclic I/O slot
Module = "FLOW IN  4 Byte"  0x42, 0x84, 0x80, 0x00 ; 4 bytes input, consistent over total length
Module = "FLOW OUT 4 Byte"  0x82, 0x84, 0x80, 0x00 ; 4 bytes output, consistent over total length

For Profile 3 the same GSD carries DPV1_Slave = 1 and an additional alarm slot declaration. When the GSD is loaded into HW Config, the slot dialog shows a Slot 0 for the DPV1 alarm handler and Slot 1 and Slot 2 for the cyclic process value. Behind a Y-Link the higher-level master will not match Slot 0 because the Y-Link does not consume it; this is the immediate cause of the diagnostic text.

Hardware and Wiring Verification

Before changing any software configuration, perform the hardware verification below. None of the steps below will fix the configuration mismatch, but each step removes a possible confound and protects the device from secondary damage during later steps.

Bus cable and termination

1. Use a Profibus cable type A only: 150 Ω nominal impedance, 24 AWG conductor, characteristic capacitance ≤ 30 pF/m, loop resistance ≤ 110 Ω/km. The Siemens part 6XV1830-0EH10 is the reference cable.
2. The shield must be bonded at every connector and at every cabinet entry. The shield continuity must be 360° around the cable, not pigtail.
3. Terminators must be ON at exactly two points: the DP master (or first slave) and the last physical device on the segment. All other terminators must be OFF. An active terminator (6ES7972-0DA00-0AA0) is preferred to a passive terminating resistor in the connector because it pulls the bus into defined state during power-up.
4. Measure the A and B lines with the bus powered but quiescent. Expect differential voltage ≥ 4 V (typ. 5 V) on the segment between the terminators, ≤ 0.5 V on segments outside the terminators.

Baud rate and bus parameters

Default Profibus DP baud rate on the MAG 6000 is auto-detect. The detected rate is shown in the device display. The Y-Link segment on the field side is an independent DP network from the higher-level master, so the baud rate is set on the field-side master of the Y-Link, not on the higher-level CP 443-5. If the bus length exceeds 100 m at 12 Mbit/s, drop to 6 Mbit/s, 3 Mbit/s, 1.5 Mbit/s or 500 kbit/s as required. The maximum cable length L_max for a Profibus DP segment at a given baud rate b follows the conservative rule:

L_max [m]  ≈  1000 · (12 Mbit/s) / b        for cable type A
            =  100 m  at 12 Mbit/s
            =  200 m  at 6  Mbit/s
            =  400 m  at 3  Mbit/s
            =  600 m  at 1.5 Mbit/s
            =  1200 m at 500 kbit/s

Address and ID Number

1. Confirm the Profibus address of the MAG 6000. The default is 126. The address is set on the device keypad (MENU → OUTPUT SETUP → PROFIBUS ADDRESS) or by the HW rotary switches on the Profibus module if present. Addresses 1..125 are valid; 0 and 126 are service addresses.
2. Read the ID Number from the device display (MENU → DEVICE INFO → PROFIBUS → IDENT NUMBER). The expected value is 8192 decimal = 0x2000 hex. The diagnostic mismatch will also appear if the device and the GSD disagree on the ID Number.
3. Confirm that Check_Ident_Number is enabled in HW Config for the MAG 6000 DP slave. Right-click the slave → Object Properties → Parameter Assignment → Check ident number must be ticked.

Step-by-Step Configuration Procedure

The procedure below is the shortest path from the reported failure to a working cyclic data exchange between the S7-400H and the MAG 6000 behind a Y-Link. It assumes STEP 7 V5.5 SPx and the SITRANS FM MAG 6000 Profibus module with firmware 2.01 rev C.

1. Replace Profile 3 with Profile 2 in HW Config

1. Open the STEP 7 project on the PG.
2. In HW Config, right-click the MAG 6000 slave in the field-side Profibus subnet of the Y-Link and choose Object Properties.
3. Switch the DP Slave Type / Module Family selection from the Profile 3 GSD (si018129.gsd) to the Profile 2 GSD (si018128.gsd or the current Profile 2 variant). To do this, remove the current slave from the subnet first, then drag the new device type from the catalog onto the same address.
4. Confirm the new Ident Number shown in the dialog matches 8192 (0x2000).

2. Configure the cyclic I/O slots

1. Open the slot table for the MAG 6000 (right-click → DP Slave Properties → Configuration tab).
2. Keep the default input slot "FLOW IN 4 Byte" in Slot 1 and the default output slot "FLOW OUT 4 Byte" in Slot 2. Do not add a DPV1 alarm slot; the Y-Link cannot consume it.
3. Set the consistency on each slot to Total Length. For 4 bytes this matches the default.

3. Set the diagnostic and parameter assignment flags

1. In the Parameter Assignment tab of the slave properties, leave DPV1 enable cleared. Behind a Y-Link the field side is a pure DPV0 segment.
2. Leave Sync and Freeze disabled unless the application explicitly requires broadcast commands.
3. Enable Check ident number.
4. Disable Fail Safe; the MAG 6000 does not support Chk_Cfg with fail-safe substitution values.

4. Compile and download

1. Save and compile HW Config (Station → Save and Compile).
2. Download the hardware configuration to the CPU (target system → PLC → Download). For an S7-400H in redundant mode, download to both CPUs.
3. Cold-restart the MAG 6000 from its display (MENU → DEVICE RESET → RESTART) to force it to re-read the GSD handshake parameters from the new configuration.

5. Verify online

1. Open Profibus Diagnostics from the PG. The MAG 6000 should now report DP Slave OK and the cyclic state Data Exchange (DX).
2. Open Monitor / Modify on the input slot. The first 4 bytes must reflect the current process value:

; Byte 0   : Status / quality  (bits: 0x01 good, 0x02 uncertain, 0x04 bad)
; Byte 1-3 : IEEE-754 float, big endian, instantaneous flow [m³/h]
;           (e.g. 0x42C80000 = 100.0 m³/h)
; Byte 4   : Status / quality  (output echo, optional)
; Byte 5-7 : IEEE-754 float, totalizer [m³] (32-bit, scaled)

If the input bytes are zero and the status byte reads 0x04 (bad), the MAG 6000 is in cyclic data exchange but the process value is invalid. Check the device's local display for an active error such as empty pipe or coil current out of range.

Diagnostic Buffer and Live Signal Checks

When the configuration does not match the slave error persists after switching to Profile 2, decode the S7-400H diagnostic buffer. The relevant event IDs and the corrective action are mapped in the table below.

On the field side, the MAG 6000 can also be read by its own display in the PROFIBUS → DIAGNOSIS menu. The hex codes returned by the device map to standard DP diagnostic blocks:

0x01  Master lock       (slave is parameterized by another master, address conflict)
0x02  Parameter fault   (PRM byte rejected)
0x04  Configuration fault (Chk_Cfg rejected)
0x08  Extended diagnostic present
0x10  Diagnostic message present (extended status, not an error)
0x20  Slave not ready   (cold-start or warm-restart pending)
0x40  Fixed at 0
0x80  Static diagnosis   (extended diagnostic block follows)

Live signal check with a Profibus analyzer

1. Connect a Profibus analyzer (e.g. Softing PROFINET Profibus BC-502-PB, Inatech, or a laptop with a Profibus PC card and a tool such as PROFIBUS Diagnostics Suite) to the field-side segment of the Y-Link.
2. Capture the startup sequence: the analyzer must show the MAG 6000 entering Wait_Prm after the master's first FDL_Status = 0x00, then Wait_Cfg after a successful PRM telegram, then Data_Exchange after a successful Chk_Cfg.
3. If the analyzer shows Wait_Cfg indefinitely, the device is rejecting the configuration. Capture the Chk_Cfg payload and compare it byte-for-byte to the GSD slot table. The first deviation is the failing slot.

Alternative Topologies: When Y-Link is Not the Right Tool

Y-Link is the right component when the higher-level CPU needs an electrically isolated sub-network, typically for safety reasons. It is the wrong component when the field devices depend on DPV1 features such as alarm routing, MS1/MS2 acyclic services, or profile-specific slot extensions. The alternatives are listed below.

If the MAG 6000 must use Profile 3 with DPV1 alarms, the recommended fix is to remove the Y-Link and replace it with a DP/PA Coupler (if the MAG 6000 is on a PA bus) or to bring the MAG 6000 onto the higher-level segment directly, accepting the loss of safety isolation. The DP/PA Coupler is the only component that preserves the Profibus PA Profile 3 condensed status and diagnostic model end-to-end.

Commissioning Verification Checklist

Run through the checklist below after the Profile 2 configuration is online. Each row must be OK before the segment is handed over to operations.

Frequently Asked Questions