Siemens S7-1200 vs S7-1500: Differences and Comparison

In short

Deciding between the Siemens SIMATIC S7-1200 and S7-1500 controllers is a foundational choice in industrial control design. This comparison details memory, processing, and communication specs to help you select the exact CPU for your application.

Overview

Within the Siemens SIMATIC industrial automation ecosystem, the S7-1200 and S7-1500 represent the absolute core of current programmable logic controllers (PLCs). Introduced as the modern successors to the legacy S7-200 and S7-300 lines respectively, both controllers operate natively inside the Siemens Totally Integrated Automation (TIA) Portal engineering framework.

While they share a similar software ecosystem, they are engineered for distinctly different machine scales:

SIMATIC S7-1200: Designed as a modular, compact controller for basic to medium-scale standalone applications. It packages onboard I/O, communication ports, and technological functions directly onto the CPU housing.
SIMATIC S7-1500: Designed as the flagship, high-performance modular controller for mid-to-large-scale factory automation, process systems, and high-speed motion control. It features an active backplane, ultra-fast bit processing speed, and modular expandability.

Key Differences at a Glance

The functional boundary between a high-end S7-1200 (such as the CPU 1217C) and an entry-level S7-1500 (such as the CPU 1511-1 PN) presents some overlap. However, structural and backplane differences clearly define their target workloads.

Feature / Metric	SIMATIC S7-1200	SIMATIC S7-1500
System Architecture	Compact, monolithic design with fixed integrated I/O.	Fully modular backplane design; external physical standard I/O modules.
Backplane Speed	Moderate speed (optimized for localized serial expansion).	High-speed active backplane bus (with ultra-low bus cycle times).
Onboard Display	None. Diagnostic LEDs only.	Built-in color display on standard CPUs for network setup and diagnostics.
Languages Supported	LAD, FBD, SCL. (STL & GRAPH not natively supported).	LAD, FBD, SCL, STL, GRAPH, C/C++ (ODK variants).
Fail-safe (Safety) Option	Yes (F-CPUs available, e.g., CPU 1214FC).	Yes (F-CPUs, up to SIL 3 / PL e capability).
Redundancy Options	None natively supported at CPU level.	High availability (R/H redundant CPU architectures).

Specifications Comparison

To match the correct PLC to your plant or machinery specifications, analyze the hard mechanical and electronic limitations below.

Parameter	SIMATIC S7-1200	SIMATIC S7-1500
Controlled Drive Range	Micro to medium systems (Fractional to ~75 kW typical via basic PROFIBUS/PROFINET).	Unlimited (Multi-Megawatt multi-drive topologies utilizing PROFINET IRT).
CPU Supply Voltage	24 VDC, 120 VAC, or 230 VAC (model-dependent).	24 VDC (system power supplies can convert 120/230 VAC to internal bus power).
Control Modes & Motion	Open/Closed Loop PID, Basic Motion (PTO/PWM up to 4 axes at 1 MHz).	Advanced Motion Control (Isochronous Mode, Camming, Kinematics, Interpolation).
Communication Protocols	PROFINET (RT), Modbus TCP/RTU, TCP/IP, ISO-on-TCP, USS, OPC UA (Basic Server).	PROFINET (RT/IRT), PROFIBUS DP, OPC UA (Full Server/Client, Companion Specs).
Work Memory (Max)	Up to 150 KB (CPU 1217C).	Up to 10 MB Program / 40 MB Data (CPU 1518-4 PN/DP).
Load Memory (Max)	Up to 4 MB onboard (expandable to 32 GB using SIMATIC Memory Card).	Requires SIMATIC Memory Card (SMC) up to 32 GB (no internal load memory).
I/O Capacity (Local)	Max 8 Signal Modules (SM) + 1 Signal Board (SB) + 3 Comm Modules (CM).	Max 32 local modules on a single rack.
Lifecycle Status	Highly Active (SIMATIC S7-1200 G2 generation announced / in deployment).	Highly Active (Flagship system with continuous performance upgrades).

Performance & Capabilities

The core performance difference of the S7-1500 compared to the S7-1200 is characterized by its superior raw command execution speed.

Bit Instruction Processing Speeds

S7-1200 (CPU 1214C/1215C/1217C): Processes a boolean bit instruction in approximately 80 to 85 nanoseconds (ns).
S7-1500 (CPU 1511-1 PN up to 1518-4 PN): Processing speeds start at 60 ns on the entry-level 1511 and drop to an incredibly fast 1 ns on the high-end 1518 processor.

High-Speed Backplane Bus

The S7-1500 features a fast backplane bus integrated with a high baud rate, enabling the rapid transmission of signal module state changes directly to the CPU's memory registers. This configuration allows for Isochronous Mode operations, where the output signal update, program execution cycle, and communication bus frame synchronization occur deterministically down to sub-millisecond ranges. The S7-1200 does not support isochronous real-time (IRT) clock synchronization, making it unsuitable for highly synchronized multi-axis servo coordination.

Programming & Software

Both devices are configured using the Siemens TIA Portal software. However, the software Licensing structures and structural code capabilities diverge of these two lines.

       ┌────────────────────────────────────────────────────────┐
       │                 TIA PORTAL FRAMEWORK                   │
       └──────────────────────────┬─────────────────────────────┘
                                  │
         ┌────────────────────────┴────────────────────────┐
         ▼                                                 ▼
┌──────────────────┐                              ┌──────────────────┐
│ STAGE 7 BASIC    │                              │ STAGE 7 PROF.    │
│ (Cost-Effective) │                              │ (Full Scope)     │
└────────┬─────────┘                              └────────┬─────────┘
         │                                                 │
         ▼                                                 ▼
┌──────────────────┐                              ┌──────────────────┐
│  SIMATIC S7-1200 │                              │  SIMATIC S7-1500 │
│  - Basic logic   │                              │  - Full STL/GRAPH│
│  - LAD/FBD/SCL   │                              │  - C++ ODK Integration
│  - Basic Motion  │                              │  - Complex Motion│
└──────────────────┘                              └──────────────────┘

Software Licensing

STEP 7 Basic: Licensed at a lower price point, this software package targets only S7-1200 controllers and basic HMI panels.
STEP 7 Professional: Required to program, simulate, and commission the S7-1500 line. Step 7 Professional maintains full backward compatibility for the S7-1200.

Code Organization & Languages

While the S7-1200 accommodates standard logic loops written in Ladder (LAD), Function Block Diagram (FBD), and Structured Control Language (SCL), it excludes Statement List (STL) and GRAPH (sequential programming). The S7-1500 executes all five standard IEC 61131-3 languages natively, giving engineering teams the flexibility to write complex procedural routines using STL or manage sequence steps via GRAPH.

Communication & Networking

Modern industrial architectures rely heavily on horizontal and vertical industrial communication channels.

Industrial Ethernet Capabilities

S7-1200: Offers 1 or 2 RJ45 ports (dependent on model) acting as a single, common internal PROFINET IP address Interface. It operates strictly on PROFINET RT (Real-Time).
S7-1500: Mid-to-high-spec models (e.g., CPU 1516-3 PN/DP) offer multiple separate PROFINET interfaces with distinct IP addresses. This physical separation prevents traffic bottlenecks by letting you segment local I/O network networks from supervisory SCADA/MES networks. Additionally, the S7-1500 supports highly synchronized PROFINET IRT (Isochronous Real-Time) networks.

OPC UA Implementation

S7-1200 (Firmware v4.4+): Functions as a basic OPC UA Server. Its limited processing power restricts tag counts and subscription speeds.
S7-1500: Offers full-scale OPC UA Server and Client architecture. It supports encrypted communication, Companion Specifications (such as OMAC PackML or Weihenstephan), and user-defined method calls handled directly on the CPU.

Pricing & Lifecycle

The total cost of ownership (TCO) and long-term hardware availability are critical factors for design and maintenance teams.

Initial Capital Expenditure

S7-1200: Extremely cost-efficient. The hardware's compact size and integrated I/O points reduce the initial cost of ownership, making it ideal for high-volume OEMs.
S7-1500: Premium industrial pricing applies. Beyond the initial CPU investment, system integration costs must also account for mandatory SIMATIC Memory Cards (SMCs) and front rail-connector systems.

Hardware Lifecycle & Availability

Both families are highly supported and active within the Siemens roadmap:

S7-1200 G2: Siemens has announced the next generation S7-1200 (G2), ensuring long-term parts availability, firmware security upgrades, and engineering support for the compact controller tier until at least 2040.
S7-1500: Serves as the key focus for Siemens' industrial automation portfolio. It receives regular firmware upgrades to support modern cybersecurity features like secure communication protocols and legacy migrations.

When to Choose Each

Select the S7-1200 If:

Space Constraints Exist: The target panel demands a small footprint with direct DIN-rail mounting.
Highly Cost-Sensitive: Perfect for straightforward conveyor modules, standalone pumping skids, basic aggregate systems, and ventilation control panels.
Low I/O and Small Motor Counts: Perfect for applications utilizing simple VFDs via Modbus RTU or analog controls with fewer than 150 local physical digital connection points.
Basic Positioning Needs: Ideal for simple motor controls requiring only 1 to 4 basic PTO axes.

Select the S7-1500 If:

Interpolated, Multi-Axis Motion is Crucial: Required for packaging systems, sorting grids, robotic gantry controls, and high-speed flying shears.
Substantial Memory Demands: The program processes large recipes, massive SQL database transfers, or handles extensive diagnostic alarm listings.
High-Security & Regulation Standards: Essential for regulated chemical plants or medical manufacturing lines requiring OPC UA encryption and physical CPU run/stop locking.
System Redundancy: Essential for water processing, manufacturing facilities, or hazardous industrial applications where downtime is costly.

Migration & Upgrade Path

Upgrading an S7-1200 application to an S7-1500 in TIA Portal is a straightforward software conversion, but does require some manual adjustments.

┌─────────────────────────────────┐
│     Siemens S7-1200 Source      │
└────────────────┬────────────────┘
                 │
                 │ 1. Open TIA Portal System Design
                 ▼
┌─────────────────────────────────┐
│       Right-Click CPU           │
│    "Change Device" Utility      │
└────────────────┬────────────────┘
                 │
                 │ 2. Select S7-1500 target model
                 ▼
┌─────────────────────────────────┐
│    Automatic Address Mapping    │
└────────────────┬────────────────┘
                 │
                 │ 3. Resolve Compile Errors:
                 │    - Replace local S7-1200 HW IDs
                 │    - Convert PTO motion to TOs
                 │    - Wire physical modular terminals
                 ▼
┌─────────────────────────────────┐
│     Siemens S7-1500 Target      │
└─────────────────────────────────┘

Hardware Swapping: Open the TIA Portal hardware configuration view, right-click the S7-1200 CPU, and choose "Change device". Then, select your chosen S7-1500 model.
Addressing Allocation: Standard non-localized inputs/outputs register seamlessly, but any unique integrated analog input locations on the S7-1200 (e.g., standard IW64/IW66) must be manually remapped to S7-1500 modular system cards.
Technology Object Conversion: Basic PWM or High-Speed Counter (HSC) configurations mapped directly to S7-1200 hardware registers must be reconfigured to use the standard S7-1500 Technology Object blocks.
Wiring Harnesses and Footprint: Note that S7-1500 modules require unique front connector wiring blocks, meaning you will need to completely re-wire the physical terminal blocks during an upgrade.

Frequently Asked Questions

1. Can I use S7-1200 expansion modules directly on an S7-1500 system rack?

No. The physical backplane connectors and bus architecture are completely different. S7-1200 modules slide together on simple side pins, whereas S7-1500 modules use a dedicated high-speed modular backplane connector (U-connector) system on an active Din-Rail.

2. Is a SIMATIC Memory Card (SMC) mandatory for both PLCs?

No. S7-1200 PLCs have integrated, non-volatile load memory and can run without an SD card. In contrast, S7-1500 controllers do not have internal load memory and require a SIMATIC Memory Card (SMC) to run.

3. Does the S7-1200 support fail-safe (Safety) programming?

Yes. The fail-safe variants (e.g., CPU 1212FC, 1214FC, 1215FC) support SIL 3/Category 4/PL e functional safety standards. You can program safety functions along with standard logic within TIA Portal when using the STEP 7 Safety Basic add-on license.

Understanding Siemens TIA Portal Licensing Options
How to Choose the Correct SIMATIC Memory Card for S7-1500 controllers
Configuring PROFINET RT and IRT on Siemens S7 Systems
Retrofitting Legacy S7-300 PLCs to SIMATIC S7-1500