Siemens 6ES7315-2EH14 CPU Replacement

Overview

The Siemens SIMATIC S7-300 system remains one of the most widely deployed modular PLC lines globally. At its core, the 6ES7315-2EH14-0AB0 CPU 315-2 PN/DP has served as a reliable industrial control platform, integrating both PROFIBUS DP and PROFINET communication.

However, as Siemens transitions the S7-300 to legacy status (Product Milestone PM400/PM410), keeping industrial lines running requires a clear replacement and migration strategy. Programmers and maintenance managers must decide whether to perform a drop-in replacement with a successor S7-300 CPU or execute a modernization program migrating to the current SIMATIC S7-1500 system. This guide provides the technical specifications, compatibility mappings, and transition steps needed for both options.

Legacy Product Information (6ES7315-2EH14-0AB0)

The 6ES7315-2EH14-0AB0 is a mid-range S7-300 processor designed for installations demanding high-speed instruction execution, local and distributed I/O, and flexible industrial communications.

• Catalog Part Number: 6ES7315-2EH14-0AB0
• Family: SIMATIC S7-300
• Processor Performance: 0.05 microseconds per bit instruction; 0.09 microseconds per word instruction.
• Work Memory: 384 KB integrated work memory (non-volatile via SIMATIC Micro Memory Card / MMC).
• Integrated Interfaces:
  • Interface 1 (X1): Combined MPI (Multi-Point Interface) and PROFIBUS DP master/slave interface (RS485 physical layer, up to 12 Mbit/s).
  • Interface 2 (X2): PROFINET IO-Controller / IO-Device with an integrated 2-port switch (RJ45, 10/100 Mbit/s).
• Memory Card Requirement: Requires a SIMATIC Micro Memory Card (MMC) up to 8 MB for operation (non-volatile program and data storage).
• Software Compatibility: Configured via STEP 7 Classic (V5.5 SP2 or higher) or TIA Portal (V11 or higher).
• Current Lifecycle Status: Discontinued/Legacy. Replaced officially by Siemens with the 6ES7315-2EH15-0AB0.

Recommended Replacements

Depending on the operational goals, engineers can choose a direct "drop-in" S7-300 hardware replacement or migrate to the current SIMATIC S7-1500 standard.

Compatibility Considerations

Program code & Software Compatibility

Replacing a 6ES7315-2EH14-0AB0 with the successor 6ES7315-2EH15-0AB0 requires zero software rewrite. The firmware execution is backwards compatible. You can load your existing compiled STEP 7 Classic project straight onto the newer version, or configure it in TIA Portal.

Migrating to the S7-1500 platform requires transforming your software environment:

• **Legacy Code: ** Statement List (STL) compiler restrictions and direct block addressing (e.g., using absolute DB pointers like DB1.DBX0.0) must be adjusted for S7-1500's Optimized Block Access.
• **SFCs/SFBs: ** System Function Calls specific to the S7-300 firmware (e.g., SFC20 BLKMOV or SFC51 RDSYSST) are replaced by modern symbolic functions in the S7-1500 S7-Instruction set.

Hardware Layout & Form Factor

• S7-300 Successor (2EH15): Fits the exact same 40mm wide profile. The front connections, power supply wiring, and MMC slot remain identical.
• S7-1500 Series: Requires a completely different mechanical profile. S7-1500 modules mount on a proprietary S7-1500 DIN rail. Standard 35mm top-hat DIN rail is not supported natively.

IO Configurations and Networks

If migrating to an S7-1500 processor, the S7-300 local I/O modules (SM 321, SM 322, etc.) cannot be connected to the S7-1500 backplane. You must either:

1. Complete a full I/O hardware swap to S7-1500 modules.
2. Repurpose the existing S7-300 rail as a distributed I/O station by replacing the CPU 315 with an IM 153-4 PROFINET Interface Module (or IM 153-2 PROFIBUS Module), transforming the local rack into an ET 200M distributed I/O station.

Upgrade Benefits

Migrating to the S7-1500 family offers significant performance, maintenance, and security upgrades:

• Processing Speeds: Instruction execution drops down to the nanosecond range (1.5 to 10 ns for bit operations), reducing PLC cycle times and improving machine response.
• On-board Diagnostic Display: S7-1500 CPUs contain a built-in color display to read real-time diagnostics, register status, IP address settings, and firmware revisions without a programming laptop.
• Security: Advanced integrated security levels, including copy protection, block security, and password-protected firmware access.
• Long-Term Support: Standardizing on S7-1500 ensures replacement part availability for another 15 to 20 years, protecting plants from obsolete system risks.

Common Migration Challenges

• The S7-300 MMC Card: The MMC card used in the 6ES7315-2EH14-0AB0 operates on a proprietary file system. It cannot be read or written to by a typical PC card reader without corrupting it. S7-1500 uses a different, standard-format SD card system (SIMATIC Memory Card or SMC).
• PROFIBUS to PROFINET Topology: The 6ES7315-2EH14-0AB0 had an onboard PROFIBUS port. Standard S7-1500 CPUs (like the 1511-1 PN) only feature RJ45 PROFINET ports. Retaining local PROFIBUS communication requires adding a CM 1542-5 PROFIBUS DP Master Module or utilizing a PN/DP coupler.
• Wiring Terminations: S7-300 I/O modules use 20-pin or 40-pin screw/push-in front connectors. If you migrate the actual I/O to S7-1500, you must completely re-wire the field terminations unless you employ specialized migration front-connection adapters.

Step-by-Step Replacement Procedure

Scenario A: Replacing with the Drop-In Succession Model (6ES7315-2EH15-0AB0)

1. Perform a Backup

1. Connect to the existing 6ES7315-2EH14-0AB0 using STEP 7 Classic or TIA Portal via MPI or Ethernet.
2. Go Online and select "Upload Station to PG...". Save this project as a recovery backup.
3. If the processor is dead, locate the latest version-controlled project archive on your local network.

2. Power Down and LOTO

1. Turn off all power to the PLC system. Confirm that zero voltage resides across the primary target CPU nodes using a digital multimeter.
2. Apply appropriate Lockout/Tagout (LOTO) protocols to the cabinet isolating switches.

3. Remove the Legacy Processor

1. Swing open the front connection doors of the CPU.
2. Unplug the RJ45 PROFINET connectors from the X2 interfaces.
3. Unplug the DB9 sub-D connector from the X1 (MPI/DP) interface.
4. If wired directly, disconnect the 24V DC auxiliary power supply terminal block from the top left of the CPU.
5. Push down the plastic slide tab on the MMC slot and extract the SIMATIC MMC.
6. Use a flathead screwdriver to loosen the center mounting screw anchoring the CPU to the S7-300 profile rail.
7. Pivot the CPU forward and lift it clear from the backplane bus connector.

4. Install the Successor CPU

1. Attach the S7-300 backplane bus connector to the rear of the new 6ES7315-2EH15-0AB0 CPU.
2. Hook the top of the new CPU onto the S7-300 profile rail and pivot down until it rests flat.
3. Tighten the central mounting screw to secure the unit to the rail.
4. Insert the original legacy SIMATIC MMC into the MMC slot.
5. Reinsert the 24V auxiliary power connection, ensuring correct polarity (+24V to terminal 1, M to terminal 2).
6. Reconnect the RJ45 PROFINET networks and the MPI/PROFIBUS connectors to their matching interfaces.

5. System Restart and Verification

1. Remove LOTO brackets and apply 24V DC control power to the rack.
2. Observe the self-test sequence. The STOP LED should light steady.
3. Navigate to STEP 7 or TIA Portal and check online diagnostics. Ensure the MMC data blocks have loaded.
4. Switch the selector switch to RUN position. The green RUN LED should illuminate, indicating normal operation and communications.

---

Scenario B: Migrating to an S7-1500 CPU Platform

Legacy S7-300 Setup                     Migrated S7-1500 Setup
+------------------------+              +------------------------+
| 6ES7315-2EH14-0AB0 CPU |              | 6ES7511-1AL03-0AB0 CPU |
| [MPI/DP]   [PROFINET]  |              |        [PROFINET]      |
+------------------------+              +------------------------+
                                                    |
                                                    v
                                        +------------------------+
                                        | Optional: CM 1542-5    |
                                        |        [PROFIBUS]      |
                                        +------------------------+

1. Software Code Conversion

1. Open TIA Portal (V13 SP1 up to current versions).
2. Use the "Migrate Project" wizard. Select your legacy S7-300 .s7p (STEP 7 Classic V5.5) or .ap1x file.
3. Resolve any block compilation errors flagged by TIA Portal regarding discontinued system blocks (SFCs/SFBs).
4. Swap the hardware configuration inside TIA Portal: replace the S7-300 rack object with an S7-1500 CPU 1511-1 PN or CPU 1513-1 PN.
5. Compile the migrated code to ensure zero compilation errors.

2. Physical Rack Re-structure

1. Turn off system power and decouple S7-300 rail modules.
2. Mount the S7-1500 profile rail in the panel space.
3. Install the S7-1500 Power Supply module and the S7-1500 CPU.
4. Wiring Adapter Approach: Connect S7-300-to-S7-1500 Migration Front Connector Adapters to minimize rewiring, or wire field devices to new S7-1500 I/O terminal modules.

3. Network Integrations

1. Connect the RJ45 PROFINET cables to the S7-1500 active PROFINET ports.
2. If old PROFIBUS networks are connected, mount a CM 1542-5 communication module next to the S7-1500, and connect the PROFIBUS Sub-D cable.

4. Program Download

1. Power up the S7-1500 system.
2. Connect your programming PG via PG/PC interface on the target Ethernet port.
3. Assign the configured IP address and PROFINET Device Name via TIA Portal "Online & Diagnostics."
4. Download the newly compiled program hardware configuration and software blocks to the CPU.
5. Put the S7-1500 in RUN mode using the integrated display panel or the software menu.

Frequently Asked Questions

Can I run a 6ES7315-2EH15-0AB0 CPU with my old S7-300 program without making any modifications?

Yes. The 6ES7315-2EH15-0AB0 is a direct functional replacement. The memory layout, block handling, and physical communication ports are fully compatible. You can write your existing program directly to the new CPU.

What is the maximum size SIMATIC MMC card I can use in the S7-300 CPU?

The 6ES7315-2EH14-0AB0 and its successor can address up to an 8 MB SIMATIC MMC. However, for most programs, a 512 KB or 2 MB card is adequate. Do not use standard off-the-shelf SD cards, as they will not fit or function.

How do I migrate my PROFIBUS networks to a PROFINET-only S7-1500 CPU?

If your legacy setup used the local S7-300's MPI/DP port to talk to local drives or remote nodes, you can either add a CM 1542-5 communication module to the S7-1500 system rack or configure a PN/DP Link gateway to route communications between the networks.

What should I do if my legacy CPU fails and I do not have a backup file?

You can pull the SIMATIC MMC from the dead 6ES7315-2EH14-0AB0 and insert it directly into a functioning spare 6ES7315-2EH15-0AB0. The CPU load memory resides entirely on the MMC. Once powered, the CPU reads the user blocks directly from the card.

Related Products & Families

• SIMATIC S7-300 Power Supplies: PS 307 (5A, 10A models) used to supply the 24V DC bus voltage.
• SIMATIC S7-300 I/O Modules: Digital Input/Output modules (SM 321, SM 322) and Analog modules (SM 331, SM 332).
• SIMATIC S7-1500 CPUs: Standard (CPU 1511, 1513, 1516), Compact (CPU 1511C, 1512C), and Fail-Safe (F-series) controllers.
• SIMATIC Memory Cards (SMC): Used for S7-1500 controllers (e.g., 6ES7954-8LF03-0AA0).

Need Help?

Whether you are performing a drop-in replacement or executing a full legacy-to-modern platform migration, staying stocked on reliable hardware components is critical.

Palm Parts Solution specializes in sourcing high-quality new, refurbished, and surplus industrial automation products. We carry a wide selection of Siemens SIMATIC S7-300 legacy components, micro memory cards, and S7-1500 transition hardware. Contact us today to locate obsolete spares, verify part numbers, or plan your next machine modernization.