GSD vs GSDML Files: Profinet Device Description Compared

Overview

Device description files are the configuration backbone of every PROFIBUS and PROFINET fieldbus network. Before a controller can exchange cyclic process data with a remote I/O station, a drive, a valve island, or an identification reader, the engineering tool must know the device's module catalog, slot rules, diagnostic layout, parameter structure, and communication properties. That information is delivered to the engineering tool as a standardized machine-readable file: a GSD for PROFIBUS, or a GSDML for PROFINET.

Although the two file types are often discussed together, they are not interchangeable. They use different physical transports (RS-485 vs. Industrial Ethernet), different data models, different on-disk encodings, and different schema versioning rules. A GSD is a flat text file using a keyword/value syntax inherited from PROFIBUS DP. A GSDML is an XML document built on a formal W3C schema published by PROFIBUS & PROFINET International (PI).

This reference consolidates the technical specification details, version-to-firmware mappings, installation procedures for STEP 7 V5.x and TIA Portal, schema fields, and field-proven diagnostics that control engineers need when commissioning, replacing, or troubleshooting PROFIBUS/PROFINET devices.

Historical Context: From GSD to GSDML

The original Generic Station Description was defined in the early 1990s as part of the PROFIBUS DP standard (IEC 61158 / EN 50170). Because PROFIBUS DP was conceived as a master/slave, cyclic, RS-485-based fieldbus, the GSD only had to describe a relatively small set of fixed concepts: device identity, baud rate support, max slave diagnostics, module count, and a list of I/O modules. The text-based format was adequate and allowed integrators to inspect a GSD with a plain text editor.

When PROFINET was specified in the early 2000s, the requirements expanded significantly:

• Real-time (RT) and isochronous real-time (IRT) communication classes
• Multiple application relations (ARs) and multiple AR vendors
• Shared Device (one PN device visible to multiple controllers)
• Shared Input / Shared Output (input broadcast, output arbitration)
• I&M (Identification & Maintenance) data 0..4
• Module-internal submodules with subslot addressing
• Port statistics, LLDP neighborhood, SNMP MIBs
• Functional Safety (PROFIsafe) and PROFIenergy profiles
• Redundancy (S2, R1, R2) and system redundancy
• Web server, asset management, security (PROFINET Security Class 1)

Cramming all of this into the legacy flat-text GSD syntax was not feasible. PI therefore defined a new XML-based format called GSDML (GSD Markup Language). The first published GSDML specification, V2.0, accompanied PROFINET Conformance Class A in 2004. Subsequent revisions (V2.1, V2.2, V2.25, V2.3, V2.31, V2.32, V2.4) added the new features above in a backward-compatible XML schema.

GSD File Format (PROFIBUS) — Technical Structure

A PROFIBUS GSD is a plain ASCII/UTF-8 text file with the suffix .GSD (historically also .gsd or device-specific .gse / .gsg variants used by some manufacturers). The file is divided into three logical sections, separated by semicolons:

1. General specifications — vendor name, model, revision, hardware/firmware release, supported baud rates (9.6 kbps to 12 Mbps), max diagnostic length, max slave number, sync/freeze capability, redundancy behavior.
2. Master/slave specifications — fixed and modular station structure, maximum number of modules, max input/output data length, minimum slave interval (min T_sdr), max T_sdr, max user parameter length (User_Prm_Data_Len), and Family code (for Profile devices).
3. User parameter description (Ext-User-Prm) — bit-level definitions of the parameter telegram that the master sends to the slave during parameterization.

Each section is opened with a keyword terminated by an asterisk and closed by a semicolon. Lines may be wrapped with the backslash continuation character.

Example excerpt (Siemens ET 200S GSD, abridged):

#Profibus_DP
; GSD File for ET 200S IM 151-1 Standard
Vendor_Name        = "Siemens AG"
Model_Name         = "ET 200S IM151-1"
Revision           = "1.0"
Ident_Number       = 0x0001
Protocol_Ident     = 0
Station_Type       = 0
FMS_supp           = 0
Hardware_Release   = "1.0"
Software_Release   = "V1.0"
; Supported baud rates
9.6_supp   = 1
19.2_supp  = 1
45.45_supp = 1
93.75_supp = 1
187.5_supp = 1
500_supp   = 1
1.5M_supp  = 1
3M_supp    = 1
6M_supp    = 1
12M_supp   = 1
Max_Diag_Data_Len = 244
Max_Input_Len     = 244
Max_Output_Len    = 244
Max_User_Prm_Data_Len = 8
; Slot definitions
Module            = "DI 4x24VDC HF"  0x10
EndModule
Module            = "DO 4x24VDC/0.5A" 0x20
EndModule

Key structural elements that engineers encounter during troubleshooting:

GSDML File Format (PROFINET) — Technical Structure

A GSDML file is an XML document with the suffix .xml. The PI-maintained XML schema is published at www.profinet.com under the "PROFINET IO GSDML Specification" documents. The schema's namespace is http://www.profinet.org/xml/gsdml/ followed by the version identifier (e.g., /V2.32 for the 2.32 release).

High-level document structure:

<?xml version="1.0" encoding="UTF-8"?>
<GSDML xmlns="http://www.profinet.org/xml/gsdml/V2.32"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://www.profinet.org/xml/gsdml/V2.32 ...">
  <Profile>
  <ProfileBody>
    <DeviceIdentification VendorID="0x002A" DeviceID="0x0301" .../>
    <DeviceFunction>...</DeviceFunction>
    <ApplicationProcess>...</ApplicationProcess>
    <ExternalProfileList>...</ExternalProfileList>
  </ProfileBody>
  </Profile>
</GSDML>

Inside ProfileBody the most important elements are:

Because the GSDML schema is XML, it is hierarchical, extensible, and fully self-describing. PI performs strict XML schema validation before publishing certified device GSDML files, and engineering tools reject malformed or non-conformant GSDML files at import time.

Side-by-Side Technical Comparison

GSDML Version → PROFINET Feature Mapping

Each GSDML version corresponds to a specific PROFINET specification and TIA Portal / STEP 7 minimum release. The table below is derived from the PI PROFINET IO GSDML Specification documents and Siemens support entries.

Installation in TIA Portal

TIA Portal stores GSDML files in a per-version library directory. The default locations are:

C:\ProgramData\Siemens\Automation\Portal Vxx\Data\Hmi\Catalog   (HMI faceplates)
C:\ProgramData\Siemens\Automation\Portal Vxx\Data\HsysBsp
C:\ProgramData\Siemens\Automation\Portal Vxx\Devices

Installation procedure:

1. Download the GSDML-Vx.x-…xml from the device manufacturer's product page (Siemens Support support.industry.siemens.com, or the vendor's download portal).
2. In TIA Portal, open the project, switch to the Device & Networks view.
3. Click Options → Manage general station description files (GSD).
4. Browse to the XML file, select it, and click Install.
5. TIA Portal validates the file against its supported GSDML schema. If validation fails, an error code is shown in the lower pane.
6. The device then appears in the Hardware catalog → Other field devices → PROFINET IO → [Vendor] → [Product] tree.

Common install error codes (from the import log):

Installation in STEP 7 V5.x

STEP 7 V5.5 (with K5.5 update for PROFINET) and V5.6 handle GSDML as well. The GSDML has no relation to TIA Portal specifically — it is also used with classic STEP 7, as the PI specification is tool-agnostic.

1. Copy the GSDML file to C:\Program Files (x86)\Siemens\Automation\SIMATIC Manager\S7DATAGSD\PNIO (default path for V5.6).
2. Or, in SIMATIC Manager, open HW Config and choose Options → Install GSD File.
3. Select the XML file; the import is identical to the GSD import of classic PROFIBUS files.
4. Devices become available in the catalog under PROFINET IO → [Vendor].

PROFIBUS GSD Installation (for comparison)

1. Copy the *.GSD (and any associated *.NCM or *.BMP icon files) into ...\SIMATIC Manager\S7DATAGSD\.
2. Close and reopen HW Config so the catalog is rescanned.
3. The new slave appears in PROFIBUS DP → [Vendor].

GSD files do not need admin rights to install and are far smaller (typically 4–40 kB) than GSDML files.

Using the Device in a Project

PROFIBUS (GSD)

1. Drag the slave from the catalog to the PROFIBUS subnet line.
2. Assign a unique PROFIBUS address (0..126, default 0 is reserved for masters).
3. Open the slave's slot table and insert the modules in the correct slots (matching the physical hardware).
4. Edit Properties → Parameter assignment to set the user-prm bits (e.g., diagnostics enable, fail-safe mode, watchdog behavior).
5. Compile and download; the master will only establish the cyclic relationship if the Ident_Number read from the live device matches the one declared in the GSD.

PROFINET (GSDML)

1. Drag the device from the catalog to the PROFINET subnet.
2. Assign a unique device name and IP address (or use DHCP / DCP via PRONETA).
3. Configure the DAP and slot/subslot structure.
4. Adjust Properties → Parameters (per-module parameter telegram, I&M data, Shared Device mapping, MRP role, fast startup enable).
5. For PROFIenergy / PROFIsafe, insert the corresponding profile submodule.
6. Compile and download the device's PROFINET name using the Assign PROFINET device name tool.

Validation, Diagnostics, and Common Failure Modes

Field-Validation Procedure

1. Open TIA Portal → Online → Accessible nodes. Confirm the device responds at its IP.
2. For PROFIBUS, run Online → Diagnostics → PROFIBUS diagnostics; verify the live Ident_Number matches the configured GSD.
3. For PROFINET, launch Online → Diagnostics → PROFINET diagnostics or use PRONETA to dump live module configuration and compare with the project.
4. Check the device's Maintenance → I&M 0..4 data; the order number, serial, and firmware must match what is physically installed.
5. Use Wireshark with a TAP or port mirror to capture DCP packets and confirm the PROFINET name resolution works.

Lifecycle: Updating GSD/GSDML Files

Manufacturers release new GSD/GSDML files whenever a device's firmware is extended, new submodules are added, or a new PROFINET profile is supported. Best practice:

• Pin the version in a project archive: keep the GSD/GSDML file in the project folder so reproducible builds are possible.
• When upgrading, perform a side-by-side comparison: open the old and new GSDML in a diff tool. New versions may add default parameters, rename submodules, or shift the slot indices — each requires a device configuration review.
• Always re-read the device's I&M data after a firmware update. If the new firmware is not supported by the GSDML installed in the engineering tool, the controller will not establish an AR (Application Relationship).

Vendor-Wide Catalog Sources

• Siemens: support.industry.siemens.com → search "GSD" or "GSDML".
• PI official catalog: www.profinet.com → Device Lookup.
• Phoenix Contact, Beckhoff, SEW-Eurodrive, Balluff, Sick, Festo: each provides GSDML downloads in the product download area.

Frequently Asked Questions