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Every Siemens S7-1500 module has an order number that starts with 6ES7 followed by a string of digits and letters. That string is not random — it encodes the module type, channel count, signal type, and hardware version. Once you learn the pattern, you can identify any S7-1500 part from its order number alone.
This guide breaks down the Siemens MLFB (Machine-Readable Order Number) structure so you can decode, cross-reference, and order the right part without digging through catalogs.
What is an MLFB number?
MLFB stands for Maschinenlesbare Fabrikatebezeichnung — Siemens' machine-readable product designation system. Every Siemens automation product has a unique MLFB code that functions like a compressed datasheet. For the S7-1500 family, these codes always begin with the prefix 6ES7, which identifies the product as part of the SIMATIC S7 family.
Once you learn the MLFB structure, you can identify any module from its order number without opening a catalog.
The 6ES7 order number structure
A typical S7-1500 order number looks like this:
6ES7 5xx-xyyyz-0AB0
| Segment | Position | Meaning |
|---|---|---|
| 6ES7 | Prefix | SIMATIC S7 product family (same for S7-300, S7-400, S7-1200, and S7-1500) |
| 5xx | Digits 5-7 | Module group — identifies the category (CPU, DI, DO, AI, AO, communication, power supply, etc.) |
| xyyy | After hyphen | Module variant — channel count, signal type, and specific model within the group |
| z | Last digit before hyphen | Hardware version — 0 = first release, 1 = second revision, etc. |
| 0AB0 | After second hyphen | Firmware/packaging — 0AB0 is the standard delivery form. 0AA0 appears on some modules. |
Module group codes (5xx): the key reference
The three-digit module group code is the most useful part of the order number. Once you memorize a few key ranges, you can identify any S7-1500 module at a glance.
| Code Range | Module Type | Examples |
|---|---|---|
| 505–507 | System Power Supplies | 6ES7505-0KA00 (25W DC), 6ES7507-0RA00 (60W AC) |
| 511–518 | CPUs (standard, compact, F, T, R) | 6ES7511 (1511), 6ES7515 (1515), 6ES7518 (1518) |
| 521 | Digital Input (DI) Modules | 6ES7521-1BH00 (16 DI), 6ES7521-1BL00 (32 DI) |
| 522 | Digital Output (DO) Modules | 6ES7522-1BH01 (16 DO), 6ES7522-5HH00 (16 DO relay) |
| 523 | Digital Combo (DI/DO) Modules | 6ES7523-1BL00 (16 DI / 16 DO) |
| 531 | Analog Input (AI) Modules | 6ES7531-7KF00 (8 AI universal), 6ES7531-7QD00 (4 AI RTD) |
| 532 | Analog Output (AO) Modules | 6ES7532-5HD00 (4 AO), 6ES7532-5HF00 (8 AO) |
| 540–541 | Communication Modules (CM) | 6ES7540-1AD00 (RS485), 6ES7541-1AD00 (MPI/DP) |
| 550–551 | Technology Modules (TM) | 6ES7550-1AA01 (counter), 6ES7551-1AB01 (position) |
| 590–592 | Accessories | 6ES7590-0AA00 (U-connector), 6ES7592-1AM00 (front connector) |
| 954 | Memory Cards | 6ES7954-8LF03 (24 MB), 6ES7954-8LL03 (256 MB) |
Decoding CPU part numbers
CPU order numbers pack the most information. Let's decode 6ES7515-2AM02-0AB0 — the CPU 1515-2 PN:
| Segment | Value | Meaning |
|---|---|---|
| 6ES7 | 6ES7 | SIMATIC S7 family |
| 515 | 515 | CPU 1515 tier |
| 2 | 2 | Two PROFINET interfaces |
| A | A | Standard CPU (no safety, no technology) |
| M | M | Feature set / generation indicator |
| 02 | 02 | Hardware version 2 (third revision) |
| 0AB0 | 0AB0 | Standard delivery |
Result: 6ES7515-2AM02-0AB0 = CPU 1515-2 PN, standard variant, hardware version 2.
CPU letter codes quick reference
| Letter After Interface Digit | CPU Type | Example |
|---|---|---|
| A | Standard | 6ES7515-2AM02 → CPU 1515-2 PN (standard) |
| C | Compact (built-in I/O) | 6ES7511-1CK01 → CPU 1511C-1 PN (compact) |
| F | Fail-Safe (SIL 3) | 6ES7515-2FM02 → CPU 1515F-2 PN (safety) |
| T | Technology (motion control) | 6ES7515-2TM01 → CPU 1515T-2 PN (technology) |
| U | Technology + Fail-Safe (TF) | 6ES7515-2UM01 → CPU 1515TF-2 PN (tech + safety) |
| R | Redundancy | 6ES7515-2RM00 → CPU 1515R-2 PN (redundant) |
Decoding I/O module part numbers
I/O module numbers follow a simpler pattern. Let's decode 6ES7521-1BH00-0AB0 — a 16-channel digital input module:
| Segment | Value | Meaning |
|---|---|---|
| 521 | 521 | Digital Input module (see group table above) |
| 1 | 1 | Standard input type |
| BH | BH | 16-channel, 24 VDC (B = 24 VDC, H = 16 channels) |
| 00 | 00 | Hardware version 0 (first release) |
Common I/O channel-count codes
| Code | Channel Count |
|---|---|
| B (e.g., 1BF) | 4 channels (analog) or base indicator (digital) |
| F (e.g., 1BF) | 8 channels |
| H (e.g., 1BH) | 16 channels |
| L (e.g., 1BL) | 32 channels |
Real-world decoding examples
Here are four common S7-1500 modules decoded from their order numbers:
| Order Number | Decoded |
|---|---|
| 6ES7515-2AM02-0AB0 | CPU 1515-2 PN, standard, hardware version 2 |
| 6ES7521-1BH00-0AB0 | Digital input, 16 channels, 24 VDC, version 0 |
| 6ES7532-5HF00-0AB0 | Analog output, 8 channels, voltage/current, version 0 |
| 6ES7505-0KA00-0AB0 | System power supply, 25W, 24 VDC input, version 0 |
ET 200SP: a different numbering scheme
The SIMATIC ET 200SP is a distributed I/O system that works with S7-1500 CPUs over PROFINET. While ET 200SP modules also start with 6ES7, they use a different set of group codes — primarily in the 1xx range instead of the 5xx range used by rack-mounted S7-1500 modules.
| Code | Module Type | Examples |
|---|---|---|
| 131 | ET 200SP Digital Input (DI) | 6ES7131-6BF01 (8 DI x 24 VDC), 6ES7131-6BH01 (16 DI) |
| 132 | ET 200SP Digital Output (DQ) | 6ES7132-6BF01 (8 DQ x 24 VDC), 6ES7132-6BH01 (16 DQ) |
| 134–136 | ET 200SP Analog Input / Output / Combo | 6ES7134-6GF00 (8 AI), 6ES7135-6HD00 (4 AQ) |
| 155 | ET 200SP Interface Module (IM) | 6ES7155-6AU01 (IM 155-6 PN ST), 6ES7155-6AR00 (IM 155-6 PN HF) |
| 193 | ET 200SP BaseUnits | 6ES7193-6BP00 (BU type A0), 6ES7193-6BP20 (BU type A1) |
The key difference: S7-1500 rack modules use 5xx group codes (521 for DI, 532 for AO, etc.), while ET 200SP modules use 1xx group codes (131 for DI, 132 for DQ, etc.). The numbering logic within each group — channel count codes, voltage indicators, version suffixes — follows the same principles as S7-1500 rack modules.
One naming quirk: ET 200SP uses DQ (digital quantity output) instead of DO for digital outputs, and AQ instead of AO for analog outputs. This matches the naming convention used in TIA Portal.
Hardware version: why it matters
The two-digit hardware version at the end of the variant code (e.g., 02 in 6ES7515-2AM02-0AB0) indicates the physical hardware revision. Higher versions may add features, fix known issues, or change firmware requirements.
Key points:
- Higher hardware versions are backward compatible — a version 03 CPU will run programs written for version 01.
- TIA Portal may require a minimum software version to support newer hardware revisions. Check Siemens' compatibility list before ordering if you are running an older TIA Portal installation.
- When ordering a replacement for an existing module, the hardware version does not need to match exactly. A newer version will work in place of an older one.
The 0AB0 vs 0AA0 suffix
You will see two common suffixes after the second hyphen:
- 0AB0: Standard delivery form. Most CPUs and signal modules use this suffix.
- 0AA0: Also standard delivery but indicates a different packaging or firmware variant. Common on accessories, memory cards, and some I/O modules.
- 0BA0: Used on many ET 200SP modules (e.g., 6ES7132-6BF01-0BA0).
These suffixes do not indicate quality or feature differences — they relate to packaging and product variant classification within Siemens' ordering system.
How to look up a Siemens part number
If you have an order number and need to confirm the full specifications:
- Siemens Industry Mall: Enter the full MLFB number at mall.industry.siemens.com for the official datasheet, manual, and pricing.
- TIA Selection Tool: Use Siemens' online TIA Selection Tool to find modules by function, then get the matching order number.
- Check our inventory: Search our Siemens PLC Systems collection for in-stock availability. We carry CPUs, I/O modules, power supplies, and ET 200SP components.
Related resources
- Siemens S7-1500 Buyer's Guide — complete overview of the S7-1500 platform
- S7-1500 CPU Selection Guide — compare 1511, 1513, 1515, and 1517 CPUs
- S7-300 to S7-1500 Migration Guide — step-by-step upgrade path
Need a specific S7-1500 module?
Now that you can decode any 6ES7 order number, find the exact module you need in our Siemens PLC Systems collection. We stock S7-1500 CPUs like the CPU 1515-2 PN, power supplies, analog output modules, and ET 200SP modules — all with a 2-year warranty. If you have a part number but cannot find it listed, contact us for sourcing assistance.
Frequently asked questions
Are S7-1500 and S7-300 part numbers interchangeable?
No. Both start with 6ES7, but S7-300 modules use the 3xx group range (e.g., 6ES7321 for DI, 6ES7331 for AI) while S7-1500 modules use the 5xx range (e.g., 6ES7521 for DI, 6ES7531 for AI). The modules are physically different and cannot be interchanged. However, the numbering logic is similar — if you know how to read S7-300 part numbers, the S7-1500 system follows the same principles.
What does the "HF" designation mean on S7-1500 I/O modules?
HF stands for "High Feature." These modules support value status (quality information per channel), isochronous mode for deterministic I/O updates, and hardware interrupts. Most S7-1500 I/O modules are HF by default. The older "ST" (Standard) designation on some modules means these advanced features are not available.
How do I find the part number on a physical S7-1500 module?
The order number is printed on a label on the front face of every S7-1500 module, usually below the LED indicators. It is also visible in TIA Portal under Device view, then Module properties, then General, then Order number. For CPUs, you can also read it from the web server (http://[CPU-IP]) or the display module on the front panel.
What is the difference between S7-1500 and ET 200SP part numbers?
Both use the 6ES7 prefix, but they use different group code ranges. S7-1500 rack modules use the 5xx range (521 for DI, 522 for DO, 531 for AI, 532 for AO). ET 200SP modules use the 1xx range (131 for DI, 132 for DQ, 134-136 for analog). ET 200SP also uses a different suffix convention — most ET 200SP modules end in 0BA0 instead of the 0AB0 used by S7-1500 rack modules.