COM ET 100U Software: Locating It for SIMATIC ET 100U PLCs
Overview
COM ET 100U is the original Siemens programming tool for the SIMATIC ET 100U (also sold as SIMATIC S5-100U in many regions). It is a 16-bit DOS-based configuration and commissioning utility that works alongside STEP 5 to program, document, and diagnose ET 100U stations and their connected IM 308/C IM 308-6UA12 distributed I/O islands. Because the package was discontinued in the late 1990s, the program is no longer stocked by Siemens Industry Online Support and cannot be purchased through the standard Siemens Mall catalog. Replacement copies are issued only through a paid Support Request with regional Siemens representative offices, and only for customers who can demonstrate an active, installed ET 100U base.
This reference consolidates the known facts about the COM ET 100U package, the ET 100U hardware it targets, the related 6ES5 376-1AA11 EPROM submodule, and the practical options an integrator has when the original software cannot be located. It also documents the firmware/programming realities of working with the IM 308-6UA12, which is frequently mentioned alongside the ET 100U in service requests.
What COM ET 100U Is and Is Not
COM ET 100U is not a generic STEP 5 tool. STEP 5 (versions S5-DOS, S5 for Windows, S5 for Windows NT) handles the symbolic, statement list (STL), ladder (LAD), and function block (CSF) program editing and cross-compilation across the entire S5 family. COM ET 100U is a sibling utility whose scope is restricted to the ET 100U:
| Feature | STEP 5 (S5-DOS / S5/Win) | COM ET 100U |
|---|---|---|
| Edit STL/LAD/CSF programs | Yes | No |
| Symbol table management | Yes | Limited |
| ET 100U rack/parameter configuration | Manual | Yes (graphical) |
| IM 308-C / IM 308-6UA12 master setup | Limited | Yes |
| DP slave parameter assignment | Limited | Yes (COM ET 200) |
| Documentation of ET 100U station | Partial | Yes (config report) |
| OS | DOS / Windows (variant) | DOS only (16-bit) |
For the ET 200 distributed I/O family, the related tool is COM ET 200; for PROFIBUS DP master configuration on the S5-115/S5-135/S5-155, Siemens used COM PROFIBUS. These are three separate tools and are not interchangeable.
SIMATIC ET 100U Hardware Background
The ET 100U is a compact, modular PLC built around the S5-100U CPU 100, CPU 102, CPU 103, or the later 6ES5 103-8MA03 (CPU 103 with integrated DP). The controller uses a 9-slot backplane with screw-type terminal I/O modules. Because the ET 100U was sold in an IP20 enclosure configuration, it was common in sub-distribution panels and small machine retrofits.
| Order Number (MLFB) | Description | Role |
|---|---|---|
| 6ES5 100-8MA02 | CPU 100 base unit (no DP) | Central controller |
| 6ES5 102-8MA02 | CPU 102 | Central controller |
| 6ES5 103-8MA02 | CPU 103 (DP slave variant) | Central controller |
| 6ES5 376-1AA11 | Flash/EPROM submodule (256 KB) | Program memory on CPU 100/102/103 |
| 6ES5 308-3UC11 | IM 308-C DP master | Connects ET 100U to PROFIBUS DP |
| 6ES5 308-6UA12 | IM 308-6UA12 DP master (later rev.) | Connects ET 100U to PROFIBUS DP |
| 6ES5 441-8MA11 | Counter module | Et 100U I/O |
| 6ES5 482-8MA13 | Analog I/O | Et 100U I/O |
The 6ES5 376-1AA11 EPROM submodule carries the compiled STEP 5 program on a UV-erasable EPROM (later revisions added flash). It plugs onto the top of the CPU and is programmed externally on an EPROM burner, then transferred into the CPU. This is the module commonly associated with COM ET 100U in service threads because the COM utility can export an EPROM image (.BIN/.HEX) ready for a third-party programmer.
Why the COM ET 100U Software Is Difficult to Find
Several factors compound the unavailability of COM ET 100U:
- Product discontinuation: The ET 100U platform entered phase-out in 1996 and was officially declared successor product: SIMATIC S7-200 shortly afterwards. Active sales of all associated software stopped in parallel.
- 16-bit DOS binary: The package runs under MS-DOS 5.0 or higher (also works under Windows 9x DOS boxes), so Siemens can no longer push it through modern Windows installer channels. Distribution was historically on 3.5" 720 KB floppy disks.
- Licensed material: Siemens classifies COM ET 100U as licensed software. It is not redistributed through download portals.
- Successor product bundling: Configuration tasks for the IM 308-6UA12 were later absorbed into STEP 7 (Classic) with the COM PROFIBUS add-on (now replaced by HW Config inside TIA Portal with GSD files), reducing the market for the standalone COM ET 100U.
Official Procurement Channels
The only legitimate path for obtaining a working copy of COM ET 100U is a paid Support Request opened with a Siemens regional office. The procedure is:
- Identify the regional Siemens Industry customer service contact. In the Americas use
siemens.com/answers(Answers for Industry). In Europe use the country-specific portal undersupport.industry.siemens.com. - Open a ticket of category "Spare parts / legacy software request" and request a media copy of COM ET 100U for use on installed base equipment.
- Provide the serial number of at least one ET 100U CPU in service. Siemens verifies the installed base before issuing the licensed copy.
- Accept the licensing terms (single-site, single-engineer) and the per-seat fee. As of recent Siemens policy the license is offered for a one-time fee that is several hundred EUR/USD depending on the region; the order is processed by the Siemens Spares & Repairs team, not the standard catalog team.
- Receive a USB stick or download link with the DOS binaries plus the manual (printed order number: 6ES5 998-0DC11, German or English).
The 6ES5 998-0DC11 manual is still accessible from the Siemens documentation archive and contains the COM ET 100U command set, memory model, and the parallel-port EPROM programmer pinout. It is freely downloadable and gives you the necessary reference even without the software itself.
Installing COM ET 100U on Modern Hardware
Because the software is a 16-bit DOS binary, modern 64-bit Windows refuses to run it directly. Three workable environments are:
| Environment | Steps | Notes |
|---|---|---|
| FreeDOS / DOSBox-X | Install FreeDOS 1.3 in a virtual machine or run under DOSBox-X 0.103+. Mount the COM ET 100U folder as a drive letter, then launch COM100.EXE. |
Best for offline configuration / documentation only. |
| Windows XP Mode / Windows 7 32-bit | Install to C:\SIEMENS\COMET100; add a PATH entry. Set the NTVDM CPU flag in CONFIG.NT to 20 if running under XP. |
Supports serial programming cable (COM1). |
| Dedicated 32-bit laptop (Windows 7/10 32-bit) | Run as Administrator; install the SIGGY USB-to-TTY adapter driver if a real ET 100U is being programmed online. | Most reliable for live online functions. |
Programming the 6ES5 376-1AA11 EPROM Submodule
The EPROM submodule is the most common reason COM ET 100U is requested: a user needs to compile a STEP 5 project, export it as an EPROM image, and burn the binary to the 6ES5 376-1AA11 with a third-party programmer. The workflow is:
- In STEP 5 (S5-DOS or S5/Win), select File → Cross-assemble → Output EPROM. The result is a
.HEX(Intel HEX) or.BINfile in the project directory. - Open COM ET 100U and load the
.HEXfile using Module → Load EPROM image. Validate the checksum against the S5-CRC displayed on the CPU's 7-segment display after power-on. - Save the verified image to a programmer-compatible file:
2764.BIN,27128.BIN, or27256.BINdepending on the EPROM size fitted to the 6ES5 376-1AA11. - Program the EPROM on a hardware programmer (Data I/O, BP Microsystems, or modern Xeltek SuperPro). Verify with a blank-check and compare against the source file.
- Insert the 6ES5 376-1AA11 into the CPU socket with pin 1 aligned to the marking on the CPU. Cycle power; the CPU should boot from EPROM and display the configured operating mode on the 7-segment display (
--= run,ST= stop).
| 6ES5 376 variant | Memory | EPROM type | Typical use |
|---|---|---|---|
| 6ES5 376-0LA11 | 8 KB | 2764 | CPU 100 / 102 small projects |
| 6ES5 376-1AA11 | 16 KB | 27128 | CPU 103 / DP variants |
| 6ES5 376-1AA21 | 32 KB | 27256 | CPU 103 with full IM 308 config |
IM 308-6UA12 Configuration Notes
The IM 308-6UA12 is the PROFIBUS DP master commonly found in an ET 100U installation. While STEP 5 is sufficient for the PLC program, the DP master requires either COM ET 100U or COM PROFIBUS (depending on the firmware of the IM 308 itself) to define the DP slave parameter sets. The minimum configuration parameters are:
| Parameter | Typical Value | Notes |
|---|---|---|
| DP address (master) | 1 or 2 | Set on the IM 308 DIP switches |
| Baud rate | 1.5 Mbps (default) to 12 Mbps | Set by software; master detects peer baud |
| Diagnostic user length | 6 bytes | User-PRM length of the IM 308 |
| Number of DP slaves | up to 32 (v1) / 64 (v2) | Function of IM 308 firmware revision |
| Bus cycle time | 1.0 ms to 50 ms | User-configured |
Field-engineering caveat: The IM 308-6UA12 cannot be parameterized online with a non-Siemens master if the GSD revision does not match the slave firmware. Always export the IM308_*.* GSD files from COM ET 100U before re-importing them into STEP 7 or TIA Portal during migration.
Alternatives to COM ET 100U
When the official channel is too slow or the license fee is prohibitive, three alternatives exist, each with trade-offs:
| Alternative | Capability | Limitation |
|---|---|---|
| STEP 5 for Windows (S5W) from IBHsoftec | Edits STEP 5 programs, exports EPROM HEX, configures IM 308-6UA12 via included COM PROFIBUS module | Not free; license required |
| STEP 7 Classic (TIA predecessor) with COM PROFIBUS | Programs S7-300/S7-400 but can re-host IM 308 GSD files for new master setups | Cannot read or write the ET 100U CPU's program memory directly |
| Direct TIA Portal with S7-1200 / S7-1500 migration | Replaces the ET 100U hardware entirely | Requires hardware migration, panel re-engineering, and program re-compilation (S5 to S7 converter is partial) |
For shop-floor integrators maintaining dozens of ET 100U stations, the most common path is to keep one engineer licensed to a current S5W license (IBHsoftec) and treat the original COM ET 100U media as a museum artifact. For single-machine end-of-life situations, an S7-1200 (CPU 1211C/DC/DC or CPU 1214C) with a migration gateway such as the SIMATIC IOT2050 or a third-party protocol converter is more cost-effective over a five-year horizon.
Migration Path: From ET 100U to S7-1200 / S7-1500
- Use the S5 to S7 converter inside STEP 7 Classic (menu Options → S5/S7 Converter) to translate STL source. Expect 70-90% of standard logic to convert cleanly; counter, analog scaling, and IM 308-specific blocks must be rewritten.
- Map 6ES5 376-1AA11 program constants into S7 data blocks (DB). The EPROM image is no longer used; S7-1200 stores the program in internal flash.
- Replace the IM 308-6UA12 with a CM 1243-5 (PROFIBUS master) on the S7-1200. Reuse existing DP slaves with their GSD files.
- Migrate any HMI from ProTool/Pro or early WinCC flexible to either TIA Portal WinCC Unified or a current Comfort Panel.
- Re-commission the station with the standard TIA Portal acceptance test: STOP-RUN transition, online watch on the first 20 STL-equivalent statements, then drive each PROFIBUS slave into a forced-I/O test sequence.
Troubleshooting Matrix
| Symptom | Likely Cause | Corrective Action |
|---|---|---|
| COM ET 100U does not start on Windows 10/11 | 16-bit binary unsupported on 64-bit | Run in DOSBox-X 0.103+ or in a Windows 7 32-bit VM |
| Programming online fails with "Timeout on COM1" | AS511 cable (6ES5 734-1BD20) missing or wrong COM port | Verify TTY 25-pin cable; set COM port in SETUP.S5
|
| CPU reports "ST" on power-up, EPROM image unreadable | 6ES5 376-1AA11 not seated, or wrong checksum | Reseat submodule, re-burn, re-verify |
| IM 308-6UA12 not visible to master | DIP switch address conflict or no parameter assignment | Re-run COM ET 100U parameter export, re-import on the new master |
| Migration to S7-1200 loses counter functions | S5 counter blocks not auto-converted | Rewrite using IEC counters in SCL inside TIA Portal |
| PROFIBUS slave drops off intermittently | Bus terminator missing or baud rate mismatch | Verify 220 Ω terminators on both ends, set master to auto-baud-detect |
Documentation and Reference Links
For continued service work the following primary Siemens documents are essential and remain in the public archive:
- SIMATIC ET 100U Manual (6ES5 998-0DC11)
- SIMATIC S5-100U CPU 100/102/103 Manual
- IM 308-6UA12 PROFIBUS Master Manual
- 6ES5 376 EPROM Submodule Description
FAQ
Can I download COM ET 100U from the Siemens support website?
No. COM ET 100U is licensed software that is no longer listed in the Siemens Mall or in the Industry Online Support download center. The only legitimate source is a paid Support Request with a regional Siemens office, which requires proof of an installed ET 100U base.
What is the difference between COM ET 100U and COM ET 200?
COM ET 100U configures the SIMATIC ET 100U PLC and its IM 308-6UA12 master. COM ET 200 configures the SIMATIC ET 200 distributed I/O family. They are separate programs with different device libraries and are not interchangeable.
Can I use STEP 5 to replace COM ET 100U entirely?
No. STEP 5 (S5-DOS or S5/Win) handles program editing, but the graphical ET 100U station configuration, IM 308 parameter set, and the EPROM-image export workflow are exclusive to COM ET 100U. You need both tools for a complete project cycle.
What EPROM type does the 6ES5 376-1AA11 submodule use?
The 6ES5 376-1AA11 accepts a 27128 (16 KB) EPROM. The 6ES5 376-0LA11 variant uses a 2764 (8 KB) and the 6ES5 376-1AA21 variant uses a 27256 (32 KB). Verify the MLFB number on the submodule label before burning.
Is there a modern replacement for the ET 100U?
Siemens positions the SIMATIC S7-1200 (CPU 1211C / 1214C / 1215C) as the functional successor. The migration requires program conversion (S5 to S7 STL), replacement of the IM 308-6UA12 with a CM 1243-5, and re-commissioning in TIA Portal. Expect 70-90% of pure logic code to convert automatically.
Which Windows version is the last to run COM ET 100U natively?
Windows 7 32-bit (or Windows XP) is the last Windows release with full NTVDM support for the 16-bit DOS binary. On Windows 10 64-bit and later you must use a DOS emulator (DOSBox-X) or a 32-bit virtual machine.