SIMATIC controller families: S7-300, S7-400, S7-1200, S7-1500 and ET 200
How the Siemens controller generations differ, which engineering software each needs, how ET 200 distributed I/O fits in and what to use in a new project.
Two generations of engineering
Siemens controllers fall into two software worlds, and this matters more than the hardware:
| Classic | Current | |
|---|---|---|
| Controllers | S7-300, S7-400 | S7-1200, S7-1500, ET 200SP CPU |
| Engineering | STEP 7 V5.x (SIMATIC Manager, HW Config, NetPro); S7-300/400 can also be configured in STEP 7 Professional (TIA Portal) | TIA Portal only (STEP 7 Basic/Professional) |
| Languages | LAD, FBD, STL, SCL, GRAPH (options) | LAD, FBD, SCL; STL and GRAPH on S7-1500, not on S7-1200 |
| Data blocks | absolute addresses (DB10.DBW4) | optimized blocks without absolute addresses by default |
| Typical I/O | central racks, ET 200M, ET 200S | central modules, ET 200MP, ET 200SP |
Because optimized blocks have no fixed offsets, code that relies on absolute addressing (pointers, DBW access, Modbus mapping by offset) has to be reworked when moving from S7-300/400 to S7-1200/1500.
The controllers
- S7-300 — modular mid-range controller on a DIN-rail profile with up to four racks; MPI and PROFIBUS DP, PROFINET on PN CPUs. Many plants still run it together with ET 200M. Siemens states that the S7-300/ET 200M families remain available until 2033 and names S7-1500 with ET 200MP/SP as the platform for new projects.
- S7-400 — rack-based high-end controller for large plants and process automation, also as fail-safe (F) and fault-tolerant redundant H systems with synchronization modules; the basis of many PCS 7 systems.
- S7-1200 — compact controller with integrated I/O, signal boards and up to eight signal modules, a PROFINET port on every CPU, a web server and Modbus TCP/RTU instructions. The newer S7-1200 G2 generation has its own system manual.
- S7-1500 — the current platform for medium and large machines and plants: PROFINET IO with IRT, OPC UA, web server, trace and motion technology objects; F, T, C, R/H and software-controller variants.
ET 200 distributed I/O
| Family | Idea |
|---|---|
| ET 200SP | bit-modular I/O in IP20: an interface module (PROFINET, PROFIBUS or the multi-fieldbus IM 155-6 MF) or an ET 200SP CPU, BaseUnits carrying the potential groups, plugged I/O and technology modules |
| ET 200MP | the S7-1500 signal modules as remote I/O behind an IM 155-5 |
| ET 200S | the previous bit-modular generation, predecessor of ET 200SP |
| ET 200pro | IP65/IP67 housings mounted directly on the machine, including motor starters and converters |
Choosing for a new project
- Small machine, few I/O, one HMI: S7-1200 (or S7-1200 G2).
- Medium/large machine or plant section, motion, OPC UA, larger programs: S7-1500 with ET 200SP or ET 200MP.
- High availability: S7-1500R/H for new designs; existing S7-400H plants are maintained with their own documentation.
- Extending an existing S7-300/400 plant: stay with STEP 7 V5.x or STEP 7 Professional, keep the absolute addressing and plan the migration to S7-1500 with Siemens' availability statement in mind.
Addresses in practice
S7 is big-endian: MW10 consists of MB10 (high byte) and MB11 (low byte), so M10.0 is bit 8 of MW10. Overlapping words (MW10 and MW11) are a classic source of errors in S7-300 code — the S7 address helper shows the layout and checks overlaps.
Connections
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Sources
- SIMATIC S7-1500, ET 200MP Automation system — System Manual (A5E03461182) — Siemens AG
- S7-1200 Programmable controller — System Manual (V4.7, A5E02486680-AQ) — Siemens AG
- SIMATIC S7-300 Module data (A5E00105505-AK) — Siemens AG
- S7-400 Automation System, CPU Specifications (A5E00850746-AN) — Siemens AG
- SIMATIC ET 200SP Distributed I/O system — System Manual (A5E03576849-AR) — Siemens AG
- SIMATIC S7-300 — product page (availability) — Siemens AG
Updated 2026-10-02