Updating CPU 315-2DP Firmware via MMC: S7-300 Procedure

The Siemens CPU 315-2DP (6ES7 315-2AG10-0AB0) ships from the factory with firmware V2.0.12 as the operating system baseline. To move the controller to V2.6.11 - or any other release within the V2.6.x branch - the firmware image must be written to a Siemens-formatted Micro Memory Card (MMC) and applied at the next power-up. The MMC must be written by a Siemens Field PG, Power PG, PG 720/740 with MMC adapter, or the external SIMATIC MMC programmer (6ES7 792-0AA00-0XA0). Consumer laptop MMC readers will re-format the card in FAT, destroy the Siemens proprietary filesystem, and the CPU will refuse to boot from the corrupted media.

This reference covers the official Siemens procedures for CPU 315-2DP firmware updates, the exact STEP 7 V5.5 and TIA Portal V11+ menu paths, MMC ordering data, LED status patterns, diagnostic buffer evaluation, and the troubleshooting matrix for the most common field failures.

Overview

The SIMATIC S7-300 family uses a different firmware update mechanism than the S7-400 family. S7-400 CPUs can accept firmware (.fwu) files over MPI/PROFIBUS via STEP 7's online functions, but the S7-300 CPU family - including the CPU 315-2DP - requires the firmware image to be physically present on the MMC at power-up. The CPU detects the firmware file on the MMC, copies it into internal flash, runs a checksum verification, and only then activates the new operating system.

Two official Siemens procedures are documented for the CPU 315-2DP family:

• STEP 7 V5.5 with HW Config: PLC > Update Firmware - the canonical procedure, documented in Siemens KB 37334767 (note: KB text addresses the 6ES7 315-2AH14-0AB0, but the menu sequence is identical for the 6ES7 315-2AG10-0AB0).
• TIA Portal V11 with HW Config and Target system menus: Target system > Update firmware - documented in Siemens KB 16750732.

MLFB Identification and Firmware Compatibility

The CPU 315-2DP has been produced under several order numbers (MLFBs). Each MLFB is bound to a specific firmware branch, and firmware files are not interchangeable across MLFBs. Loading the wrong firmware image is the most common cause of failed updates in the field.

The user's controller 6ES7 315-2AG10-0AB0 is at V2.0.12 and the target is V2.6.11. Both releases belong to the same V2.6.x branch, so a direct in-place upgrade is supported. The firmware file is typically delivered as a ZIP archive containing CPU_315-2DP_V2.6.11.upd or S7300FW.upa; the exact filename depends on the Siemens support portal packaging for that build.

To read the MLFB and current firmware version on the physical CPU, navigate Online > Accessible Nodes in STEP 7 V5.5, or use Online & Diagnostics > Module Information in TIA Portal. The module order number and firmware version appear on the Identification tab.

Prerequisites and Required Hardware

Before beginning the firmware update, gather the following items. Skipping any one of them is the most common reason for incomplete or failed updates.

1. Siemens-formatted MMC - order from Siemens. Standard SD cards from consumer vendors will not work, even after manual re-formatting.
2. Siemens Field PG (e.g., SIMATIC Field PG M4/M5/M6), Power PG, or legacy PG 720 / PG 740 with MMC adapter - to write the firmware file to the MMC.
3. External MMC/PROM programmer 6ES7 792-0AA00-0XA0 - the alternative for shops that do not own a Field PG.
4. STEP 7 V5.5 SPx or TIA Portal V11 SPx or later, with the firmware image downloaded from Siemens Online Support.
5. MPI or PROFIBUS cable (only required for post-update online verification, not for the card-based update itself).
6. 24 V DC supply to the S7-300 station with sufficient hold-up time - at least 30 seconds - to ensure the update is not interrupted by a power dip.

Validate the firmware file integrity before beginning. The Siemens Online Support portal publishes the SHA-256 checksum alongside the download. Verify it with a tool such as certutil -hashfile CPU_315-2DP_V2.6.11.upd SHA256 on Windows or sha256sum on Linux. If the checksum does not match, re-download.

Required Hardware: Field PG vs. External Programmer

The choice between a Siemens Field PG and the external MMC programmer depends on shop equipment and frequency of firmware updates.

The 6ES7 792-0AA00-0XA0 external programmer is the most accessible option for a one-off update. It connects to a Windows host via USB, and the bundled Field PG Tools utility writes the Siemens filesystem and the firmware image to any SIMATIC MMC up to 8 MB. No STEP 7 installation is required for the write operation - only the firmware file.

MMC Capacity and Ordering Data

Siemens offers MMCs in seven capacity points. Not all are usable for firmware updates on the CPU 315-2DP.

The Siemens MMC Filesystem and Why Consumer Readers Fail

The SIMATIC MMC uses a proprietary block-based filesystem that is not visible to Windows, macOS, or Linux desktop operating systems. The MMC reserves a 16-byte header block at offset 0 that identifies the card as a Siemens media and contains the MMC's serial number, capacity, and write-protection flag. The remaining blocks are organized into a proprietary directory structure with type tags, content blocks, and CRC fields.

When a Siemens MMC is inserted into a consumer laptop reader, the operating system cannot interpret the proprietary header and misidentifies the card as unformatted. Windows prompts the user to format the disk in drive E: before use. macOS shows that the disk inserted was not readable by this computer. Linux attaches the card as /dev/mmcblk0 but cannot mount it.

If the user accepts the format prompt - even by reflex - the MMC's first 16-byte Siemens header is overwritten with a FAT boot sector. Once destroyed, the CPU 315-2DP will:

• Reject the card with the SF (red) LED on and the STOP LED on at power-up.
• Refuse to load any firmware or project from the media.
• Treat the card as a non-Siemens media, even though the FAT filesystem is intact.

The only recovery path is to re-format the card using a Siemens Field PG's SIMATIC Manager > File > Memory Card > Format menu, or the external MMC programmer's Re-format as SIMATIC command. The re-format is non-reversible - any prior Siemens data on the card is lost.

Operating systems sometimes attempt to write hidden system files (e.g., Windows creates System Volume Information) to any newly mounted card, which also corrupts the Siemens header. Disable auto-mount or set the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\mountmgr\NoAutoMount = 1 before inserting a Siemens MMC into a Windows host.

Downloading the Firmware from Siemens Support

The firmware file is hosted on the Siemens Industry Online Support portal. The download requires a free Siemens account.

1. Open support.industry.siemens.com in a browser.
2. In the search box, type the MLFB 6ES7 315-2AG10-0AB0 and click the result that matches the CPU 315-2DP family.
3. Click Support > Firmware in the right-hand sidebar.
4. Locate the entry CPU 315-2DP, Firmware V2.6.11. The entry lists the file size (~1.8 MB compressed), the supported MLFBs, and the changelog.
5. Click Download and accept the EULA. The file is delivered as a ZIP archive containing one or more .upd files and a PDF changelog.
6. Verify the SHA-256 checksum against the value published on the portal.
7. Extract the ZIP to a folder accessible to the Field PG.

STEP 7 V5.5 / HW Config Firmware Update Procedure (Online)

This procedure follows Siemens KB 37334767. Although the KB describes the 6ES7 315-2AH14-0AB0, the menu sequence is identical for the 6ES7 315-2AG10-0AB0.

1. Start STEP 7 and open the project that contains the CPU 315-2DP station, or create a new offline project with the CPU configured.
2. Open HW Config: double-click the Hardware object under the S7-300 station.
3. Earmark the CPU (single-click on the CPU icon in the rack).
4. Open the menu: PLC > Update Firmware - the menu item is greyed out if the marked CPU does not support firmware update, or if no online connection exists. To use this menu path, the PG must be online to the target CPU via MPI/PROFIBUS.
5. Browse to the firmware .upd file on the Field PG's disk.
6. STEP 7 prompts for confirmation of the firmware update on CPU 315-2DP. Click Yes.
7. STEP 7 reports progress in a dialog box. The CPU's RUN LED flashes; the SF LED is on. Typical duration: 1-5 minutes for V2.6.x on a CPU 315-2DP.
8. When complete, the CPU restarts. STEP 7 reports firmware update completion in the dialog.
9. Verify the new firmware version under PLC > Module Information. The Firmware field should read V2.6.11.

MMC-Based Firmware Update Procedure (Offline)

Use this procedure when the CPU is offline (not yet wired to a network) or when you do not have a Field PG with an MPI/PROFIBUS connection at the rack.

1. Insert the Siemens MMC into the Field PG's MMC slot (or the external programmer's slot).
2. Open SIMATIC Manager on the Field PG.
3. Navigate to File > Memory Card > Update Firmware (STEP 7 V5.5 SP2 or later). For older STEP 7 versions, use PLC > Update Firmware after selecting the CPU in HW Config, with the MMC inserted in the PG.
4. Browse to the firmware .upd file.
5. Click Update. The MMC slot LED on the PG blinks during the write. Do not eject the card during the write.
6. When SIMATIC Manager reports success, safely eject the MMC.
7. Power down the S7-300 station. Turn OFF the 24 V DC supply to the PS 307 power supply module.
8. Open the CPU's front door (the small plastic flap on the front face of the CPU 315-2DP).
9. Insert the MMC into the CPU's MMC slot. The slot is keyed - the card fits only one way, with the gold contacts facing into the slot.
10. Power ON the station. The CPU detects the firmware file on the MMC and begins the update:
    • SF LED: ON (red) - indicates firmware activity.
    • RUN LED: slow flash (green) - indicates update in progress.
    • STOP LED: ON (yellow) - CPU is not yet in RUN.
11. Wait 1-5 minutes. Do not interrupt 24 V DC power.
12. When the update completes, the CPU performs an automatic memory reset and restarts in STOP. The new firmware V2.6.11 is now resident in internal flash.
13. Remove the MMC if you do not intend to store a project on it, or leave it inserted and download the STEP 7 project to it via Field PG.

TIA Portal V11+ Firmware Update Procedure

The TIA Portal procedure is documented in Siemens KB 16750732.

1. Launch TIA Portal and open the project that contains the CPU 315-2DP station (or create a new device configuration that includes the 6ES7 315-2AG10-0AB0).
2. Select the CPU in the device view or the project tree.
3. Right-click the CPU and choose Target system > Update firmware from the context menu. The menu item is enabled only if the selected CPU supports the firmware update function.
4. Browse to the firmware .upd file.
5. TIA Portal prompts for the target path of the MMC. If the host is a laptop (not a Field PG), this step fails unless the card is already Siemens-formatted. You must either:
   • Pre-format the card on a Field PG, then re-insert into the laptop reader and continue, or
   • Use the laptop only to download the firmware file, then transfer the file to a Field PG for the MMC write.
6. Once written, follow steps 7-13 of the MMC-Based Firmware Update Procedure above to apply the firmware on the physical CPU.

For an online firmware update via TIA Portal (no MMC required), use the same menu path while the TIA Portal host is connected to the CPU via MPI/PROFIBUS. TIA Portal writes the firmware directly to the CPU's internal flash over the fieldbus, identical in result to the STEP 7 V5.5 procedure.

Verification, Diagnostic Buffer, and LED Status

After the CPU restarts, verify the new firmware is active through three independent methods: online query, diagnostic buffer, and LED observation.

Online Query via STEP 7 V5.5

1. Establish an online connection: PLC > Accessible Nodes (F11).
2. Select the CPU 315-2DP and click Online.
3. Open PLC > Module Information (Ctrl+D).
4. Click the Diagnostics tab. The diagnostic buffer contains a firmware-update success entry with the new version V2.6.11.
5. Click the Identification tab. The Firmware field reads V 2.6.11; the Module field reads 6ES7 315-2AG10-0AB0.

Online Query via TIA Portal

1. Right-click the CPU in the project tree and select Online & Diagnostics.
2. Expand Diagnostics in the left pane and click Module information.
3. Click the Identification area. The firmware version is displayed.
4. Open the Diagnostic buffer area. The most recent firmware-update events are listed at the top.

LED Status Patterns

Troubleshooting Matrix

Downgrade and Lifecycle Considerations

The CPU 315-2DP firmware is generally one-way upgradable within the V2.x branch. Siemens does not officially support downgrading the firmware on the CPU 315-2DP, but the procedure is the same: write the older firmware file to a Siemens MMC and apply it at power-up. The CPU's flash loader does not enforce version monotonicity.

For long-term support planning, the CPU 315-2DP (6ES7 315-2AG10-0AB0) has been in active production since approximately 2002 and is approaching the end of standard product lifecycle. Spare MMCs and Field PGs are still available from Siemens spares channels but with extended lead times. Plan migration to a successor controller (CPU 315-2 PN/DP, 6ES7 315-2EH14-0AB0) for new installations.

FAQ