Siemens SIMATIC S7 PLC Family Comparison: S7-200, S7-300, S7-400, S7-1200, and S7-1500
Siemens has produced five major SIMATIC S7 controller families over more than two decades. Selecting the correct platform - or migrating an installed base - requires comparing instruction set depth, I/O scalability, communication interfaces, programming environment, and lifecycle status. This reference consolidates the architectural and software differences between the legacy S7-200/S7-300/S7-400 lines and their modern successors S7-1200 and S7-1500, including the obligatory TIA Portal migration path from STEP 7 V5.x.
1. SIMATIC S7 Family Overview
The five S7 families serve distinct performance and application tiers. None of them share a common programming environment - the legacy lines use STEP 7 Micro/WIN or STEP 7 V5.x, while S7-1200 and S7-1500 require TIA Portal. This software boundary is the single most important constraint when planning a mixed fleet, retrofit, or migration.
| Family | Market Tier | Programming Software | Lifecycle Status |
|---|---|---|---|
| S7-200 | Micro / low-end | STEP 7 Micro/WIN | Discontinued (replaced by S7-200 SMART) |
| S7-300 | Low to mid-end | STEP 7 V5.x (SIMATIC Manager) | Phase-out announced; migration target S7-1500 |
| S7-400 | Mid to high-end / process | STEP 7 V5.x, PCS 7 | Phase-out announced; migration target S7-1500 / ET 200SP HF |
| S7-1200 | Low-end performance | TIA Portal (STEP 7 Basic) | Active product line |
| S7-1500 | Mid to high-end | TIA Portal (STEP 7 Professional) | Active product line |
2. S7-200 - Micro PLC Tier
The S7-200 was Siemens' compact micro PLC intended for stand-alone machine control with a tightly limited instruction set and low memory budget. CPUs in the 22x range (CPU 221, 222, 224, 224XP, 226) use a fixed 16-bit ladder/fbd instruction set and program in STEP 7 Micro/WIN. Communication is handled via PPI (Point-to-Point Interface) over RS-485, with optional freeport, Modbus RTU master/slave, USS drive protocol, and AS-i master via CP modules.
S7-200 Typical Limits
- Local digital I/O: up to 128 points (CPU 226) plus analog via expansion modules.
- Bit memory (M): a few kilobytes; data block capacity in tens of kilobytes.
- Program execution: floating-point math supported on 224XP and 226 only.
- No integrated Ethernet; MPI/PPI only on the port.
The classic S7-200 has been replaced functionally by the S7-200 SMART (SR/ST series CPUs), which is programmed by STEP 7 Micro/WIN SMART and adds an integrated PROFINET port. Active S7-200 stocks are increasingly limited to repair-only supply.
3. S7-300 - Compact Mid-Range PLC
The S7-300 is a modular, mid-range PLC built around a backplane that accepts up to eight I/O modules per rack (expandable via IM 360/361/365 interface modules). The instruction set is full IEC 61131-3 (AWL/STL, FBD, LAD, GRAPH, SCL, CFC). CPUs (e.g., CPU 312, 314, 315-2 DP, 317-2 PN/DP, 319-3 PN/DP) differ in work memory, bit-instruction execution time, and integrated interfaces.
S7-300 I/O and Communication
- Central I/O: up to 32 modules per segment with interface modules.
- Distributed I/O: PROFIBUS DP (master/slave) or PROFINET IO on PN/DP CPUs (via CP 343-1 or integrated PN port).
- Programming: STEP 7 V5.x using SIMATIC Manager. TIA Portal V11 and later supports a limited subset of S7-300 CPUs as a transition target.
- Communication modules: CP 340 (RS-232/422/485 ASCII), CP 341 (Modbus RTU/master/slave), CP 343-1 (TCP/IP, ISO-on-TCP, S7 communication), CP 343-1 Advanced (adds Web server and OPC).
The S7-300 is widely deployed in factory automation but has been formally announced for phase-out. Migration projects target S7-1500 using Siemens' S7-1500 migration guide (e.g., ET 200SP as remote I/O replacement for 300-style racks).
4. S7-400 - High-End and Process Automation
The S7-400 is the high-performance, large-memory PLC for plant automation. It supports up to 16 modules per central rack, redundant power supplies, hot-swappable CPUs, and redundant PROFIBUS/PROFINET networks. The flagship CPU 417-4 and CPU 410 process automation controllers deliver instruction execution times measured in tens of nanoseconds.
S7-400 Special Features
- S7-400H: fault-tolerant, redundant CPUs synchronised over fibre-optic links for fail-over operation.
- S7-400F/FH: SIL 2 / SIL 3 safety PLCs using Distributed Safety or S7 F-systems.
- PCS 7: Siemens DCS (Distributed Control System) uses the S7-400 as its controller and adds APL (Advanced Process Library) function blocks.
- Communication: integrated PROFINET (PN/PN couplers), PROFIBUS DP master with up to 125 slaves per segment, Ethernet via CP 443-1.
S7-400 spare parts availability follows the SIMATIC phase-out timeline. Migration to S7-1500 (or ET 200SP HF for distributed I/O) requires re-engineering of the program symbol table and F-library if the source project uses S7 F-systems.
5. S7-1200 - Modern Entry-Level PLC
The S7-1200 is the low-end performance successor to S7-200. It ships with an integrated PROFINET interface, configurable digital and analog I/O on the CPU body, and signal board (SB) and signal module (SM) expansion. The CPU 1211C, 1212C, 1214C, 1215C, 1217C differ in local I/O count, work memory, and bit execution speed.
S7-1200 Software Architecture
- Programmed exclusively in TIA Portal (STEP 7 Basic or Professional).
- LAD, FBD, GRAPH (Basic), and SCL available; STL is not supported.
- Up to six counters and six high-speed counters on certain CPUs; high-speed outputs for PWM and pulse-train motion on transistor-output models.
- Web server for diagnostics and user-defined pages; integrated OPC UA server on firmware V4.4 and later.
- Motion: basic positioning with TO (technology objects) - speed axis, positioning axis, external encoder - without a dedicated motion controller.
6. S7-1500 - Mid to High-End Performance PLC
The S7-1500 is the successor to S7-300 and S7-400 for mid to high-end applications. It uses a modular backplane with active backplane connectors and supports up to 32 modules per station (CPU 1518/1519). CPUs range from CPU 1511-1 PN (entry) to CPU 1518-4 PN/DP and the high-end CPU 1519-3 PN/DP with up to 60 MB program/data work memory.
S7-1500 Performance and Variants
- Standard CPUs (R/H): R = program and data on separate flash (Runtime), H = additional retentive behavior.
- F-CPUs (fail-safe): CPU 1515F-2 PN, 1516F-3 PN/DP, 1517F-3 PN/DP, 1518F-4 PN/DP, 1518F-4 PN/DP MFP - integrated safety functions up to SIL 3 / PL e per IEC 61508 / ISO 13849.
- T-CPUs (technology): Motion control functions for synchronised axes, kinematics, camming.
- MFP (Multi-Function Platform): CPU 1518F-4 PN/DP MFP and ET 200SP F-CPU variants allow execution of C/C++ routines and MATLAB Simulink models via the ODK (Open Development Kit).
- Bit instruction execution: as low as 1 ns on CPU 1518-4 PN/DP.
7. Programming Software Comparison
Programming software compatibility is the single boundary that defines the S7 generations. A project from one environment cannot be opened or compiled in the other without conversion tools.
| Family | Engineering Tool | Minimum TIA Portal Version | Languages Supported |
|---|---|---|---|
| S7-200 | STEP 7 Micro/WIN (V4.0 SP9) | Not supported | LAD, FBD, STL |
| S7-300/400 | STEP 7 V5.5 SPx / SIMATIC Manager | V11 (partial S7-300); S7-400 limited | LAD, FBD, STL (AWL), SCL, GRAPH, CFC |
| S7-1200 | TIA Portal STEP 7 Basic | V11 (initial release) | LAD, FBD, SCL, GRAPH (Basic) |
| S7-1500 | TIA Portal STEP 7 Professional | V12 (initial release) | LAD, FBD, SCL, GRAPH, STL (V15+), CFC |
Current TIA Portal releases (V18, V19) bundle engineering for S7-1200, S7-1500, ET 200, SINAMICS drives, HMI panels, and SCADA into one project. STEP 7 V5.5 SPx remains a separate tool but is the only path to maintain a legacy S7-300/400 fleet.
8. Communication Interfaces
| Family | Integrated Port(s) | Typical CPs | Key Protocols |
|---|---|---|---|
| S7-200 | PPI/MPI (RS-485) | CP 243-1 (Ethernet), CP 243-2 (AS-i) | PPI, MPI, Modbus RTU, USS, AS-i, S7 over Ethernet (CP) |
| S7-300 | MPI; DP on DP CPUs; PN on PN CPUs | CP 340/341, CP 343-1, CP 343-2, CP 342-5 | PROFIBUS DP/PA, PROFINET IO, TCP/IP, ISO-on-TCP, Modbus RTU/TCP, S7 |
| S7-400 | MPI/DP on most CPUs; PN on PN CPUs | CP 443-1, CP 443-5 Basic/Extended | PROFIBUS, PROFINET, S7-Communication, OPC, PROFINET redundancy |
| S7-1200 | PROFINET (1 or 2 port switch depending on CPU) | CM 1241 (RS-232/422/485), CP 1242-7 (GPRS), CP 1243-1 (security), CB 1241 (RS-485) | PROFINET IO controller/device, TCP/IP, ISO-on-TCP, Modbus TCP/RTU, S7, OPC UA (V4.4+) |
| S7-1500 | PROFINET (2 or 3 port switch) | CM 1542-1, CP 1543-1, CP 1545-1 | PROFINET IO controller/device, PROFINET MRP/MRPD, OPC UA server/client, Modbus TCP/RTU, S7, S7-Plus, MQTT |
Migration from PROFIBUS DP to PROFINET is the dominant pattern when upgrading from S7-300/400 to S7-1500. Siemens offers a converter gateway (PN/PN coupler) where legacy PROFIBUS segments must remain.
9. I/O Capacity and Scalability
Local I/O counts on the central rack differ significantly. Distributed I/O via PROFINET or PROFIBUS allows the S7-300/400/1500 to scale to tens of thousands of I/O points per CPU.
| Family | Central I/O | Distributed I/O (typical) |
|---|---|---|
| S7-200 | ~14 to 128 digital / 3 to 28 analog | Limited; PPI network of slaves |
| S7-300 | ~32 modules per central rack | Thousands via PROFIBUS DP / PROFINET |
| S7-400 | Up to ~16 modules per central rack, multiple racks | Tens of thousands via PROFIBUS / PROFINET |
| S7-1200 | ~14 to 40 digital / up to ~14 analog | ET 200S/SP via PROFINET |
| S7-1500 | Up to 32 modules per station (CPU 1518) | ET 200SP / ET 200MP via PROFINET (up to 1024 IO devices per CPU) |
10. Migration Paths Between Families
Siemens provides conversion tooling and recommended replacements. Key migration scenarios:
- S7-200 → S7-200 SMART: Closest functional match. STEP 7 Micro/WIN includes a project converter for the SMART series. Substitute EM (Expansion Module) part numbers per the S7-200 SMART catalog.
- S7-200 → S7-1200: Rewrite required. Use TIA Portal; retain I/O philosophy but port the program logic because the instruction set, memory model, and communication blocks differ.
- S7-300 → S7-1500: TIA Portal STEP 7 Professional supports migration of STEP 7 V5.x projects. S7-1500 uses optimised block access by default; legacy absolute addressing must be reviewed.
- S7-400 → S7-1500 / ET 200SP HF: For non-redundant systems use CPU 1518-4 PN/DP or CPU 1519-3 PN/DP. For redundant H systems use the ET 200SP HF with redundant IM 155-6 PN HF stations and a master CPU. F-systems migrate to S7-1500 F-CPUs with the F-library conversion tool.
- S7-400 PCS 7 → PCS 7 with S7-1500 controller: PCS 7 V9 supports S7-1500 controllers as of certain releases; consult the PCS 7 compatibility list for the active V-version of your plant.
11. Selection Recommendations
| Application | Recommended Family | Notes |
|---|---|---|
| Small stand-alone machine, <64 I/O | S7-200 SMART or S7-1200 CPU 1212C/1214C | Pick S7-200 SMART for budget, S7-1200 for TIA Portal alignment |
| Mid-range machine, PROFINET required | S7-1200 CPU 1215C/1217C or S7-1500 CPU 1511/1513 | Use S7-1500 if multi-axis motion control is required |
| Plant automation, large distributed I/O | S7-1500 CPU 1515/1516/1517/1518 | Pair with ET 200SP on PROFINET MRP rings |
| Process automation / DCS | S7-1500 controller within PCS 7 or legacy S7-400 with PCS 7 | Use F-CPUs if safety instrumented function is required |
| Redundant, fail-tolerant process control | S7-400H or ET 200SP HF with redundant CPU | Plan migration well before phase-out horizon |
| Functional safety (machine safeguarding) | S7-1200F or S7-1500F | Use Distributed Safety / F-CPU libraries; SIL 3 / PL e reachable |
| High-speed motion control / kinematics | S7-1500T CPU | Supports synchronised axes and camming without external controller |
12. Commissioning and Verification Notes
Regardless of family, follow these field-proven verification steps after hardware replacement or migration:
- Verify firmware compatibility between CPU, I/O modules, and engineering software before downloading the project. Use the TIA Portal "Device Configuration" diagnostics or SIMATIC Manager hardware catalog to confirm supported firmware.
- Cross-check IP addresses and PROFINET device names. PROFINET devices are addressed by name on startup; an uncommissioned device will report "station failure" even if the IP is correct.
- For S7-1500, confirm that block-access optimisation is consistent with the HMI / SCADA driver (e.g., WinCC or third-party OPC UA client). Optimised blocks hide symbolic addresses from absolute addressing, which can break legacy OPC DA tags.
- For S7-300/400 migration to S7-1500, run the STEP 7 V5.x migration tool inside TIA Portal to flag unconverted instructions, then review the conversion log before commissioning.
- Validate safety programs on F-CPUs by performing the acceptance test specified in the F-library manual and archiving the safety signature.
- Back up the project to a TIA Portal project archive (.zap) or STEP 7 S7P file before any download, and store a copy on the plant documentation server.
13. Fault and Diagnostic Considerations by Family
| Family | Diagnostic Buffer | Common Error Categories |
|---|---|---|
| S7-200 | Plain text via Micro/WIN | Communication (PPI), analog overflow, missing expansion |
| S7-300 | Detailed buffer in STEP 7 V5.x | PROFIBUS station failure, rack failure, OB not loaded, battery low |
| S7-400 | Detailed buffer in PCS 7 / STEP 7 | PROFIBUS, redundancy loss, time-out, system fault |
| S7-1200 | TIA Portal diagnostics | PROFINET diagnostics, IP conflict, OB not loaded, F-runtime error |
| S7-1500 | TIA Portal diagnostics, web server, CPU display | PROFINET MRP ring break, I/O module channel fault, F-runtime, program error OB121/OB122 |
When migrating between families, expect new diagnostic codes. Use the Siemens SIMATIC Diagnostics Toolkit or TIA Portal "Online & Diagnostics" view to translate legacy error codes to the new platform.
14. Frequently Asked Questions
Can one TIA Portal project program S7-1200 and S7-1500 together?
Yes. From TIA Portal V13 onward, STEP 7 Professional supports mixed S7-1200/S7-1500 projects with shared tag databases. STEP 7 Basic supports S7-1200 only; upgrade to Professional to add S7-1500 support.
Is the S7-300 still orderable?
The S7-300 is in the active phase-out phase. New orders are accepted within the announced phase-out window. After the last-time-buy date, only spare-part supply via repair contracts remains. Plan migration to S7-1500 before that window closes.
What replaces the S7-200 for new machines?
Use S7-200 SMART (programmed by STEP 7 Micro/WIN SMART) for low-cost applications with a similar PPI/Modbus migration, or move to S7-1200 (TIA Portal) if integration with SINAMICS drives, SIMATIC HMIs, or PROFINET is required.
Can a STEP 7 V5.x S7-300 program be opened directly in TIA Portal?
Yes. TIA Portal includes a migration tool that converts S7-300 (and selected S7-400) projects to TIA Portal representation. STL/FBD/LAD programs are converted; review the conversion log and confirm optimised block access settings.
What is the difference between CPU 1515F and CPU 1515T?
The F suffix indicates fail-safe operation (SIL 3 / PL e per IEC 61508/ISO 13849-1). The T suffix indicates technology/motion-control extensions (synchronised axes, kinematics). FT variants combine both. The standard non-F non-T CPUs run only base SIMATIC program logic.