Resolving Siemens S7-313 Upload Error 33:17106 MMC Card Fault

Problem Definition

When attempting to upload a STEP 7 project from a SIMATIC S7-313 CPU using SIMATIC Manager V5.4 SP3 over an MPI USB PC Adapter, the operation aborts with the dialog error:

Error 33:17106 — "Communication Link to the adapter is damaged" (Verbindung zum Adapter ist gestört).

The error appears at the very first handshake between STEP 7 and the target CPU, before any block read is performed. Two diagnostic facts narrow the root cause to the CPU's removable storage rather than the PC side:

1. The same PC, the same USB MPI Adapter, and the same cable successfully upload other S7-300 stations in the plant — confirming that the hardware path (USB driver, COM port mapping, MPI bus termination, and PC Adapter firmware) is healthy.
2. Swapping the Micro Memory Card (MMC) on the affected CPU restores the upload path. Reinserting the original MMC reproduces the error on the same CPU, on other S7-313 CPUs, and on a brand-new replacement CPU installed in the same slot.

This pattern isolates the fault to the MMC itself, not to the CPU, the backplane, or the PC Adapter.

Affected Hardware and Software

Root Cause Analysis

Error 33:17106 is a STEP 7 error class 33 (online interface / adapter) and code 17106 (0x42E2 — adapter communication interrupted). It does not, by itself, prove that the MMC is at fault; STEP 7 can raise the same code when:

• The PC Adapter USB drops characters because the COM port mapping is wrong.
• The MPI bus is unterminated or terminator-only-on-one-end.
• The CPU is in STOP-with-fatal-error and cannot service MPI requests.
• The MMC has internal CRC faults, write-protect, or a corrupted directory structure.
• Know-how-protected or password-encrypted blocks trigger an early abort during the upload of the project header.

The diagnostic matrix that resolves the ambiguity is:

In the reported case, all four rows produced the same pattern: only the suspect MMC is non-functional. The machine keeps running with the suspect MMC installed (the CPU can still execute the loaded blocks from RAM), but any attempt to read the offline image through STEP 7 fails at the very first Online → Accessible Nodes request.

Diagnostic Procedure

Run the following checks in order before declaring the MMC defective. Each step is cheap and reversible.

Step 1 — Verify the PC Adapter Channel

1. Open SIMATIC Manager → Options → Set PG/PC Interface.
2. Set the access point S7ONLINE to PC Adapter (MPI) -> USB (or PC Adapter (Auto) for newer adapters).
3. In Properties, confirm the local MPI address (default 0), the highest MPI address (default 15), and the transmission rate (187.5 kbps for S7-313).
4. From the Windows Control Panel, confirm that the PC Adapter enumerates as a virtual COM port and that no other application holds it open (Siemens COM-monitor, Putty, HyperTerminal, etc.).

Step 2 — Verify the MPI Bus

• Terminate the bus at both physical ends with 220 Ω terminators (or use the active terminator on the PC Adapter cable).
• Confirm that the MPI address of the target CPU is unique on the bus and that its highest MPI address is set higher than the actual address — STEP 7 scans up to that address.
• Cycle power on the S7-313 and watch the SF / BF / DC5V LEDs. A steady SF with a flashing pattern other than the request-from-PG blink usually means a hardware fault that also blocks online access.

Step 3 — Read the CPU Diagnostic Buffer

Even when upload fails, the diagnostic buffer can usually be retrieved through PLC → Diagnostics/Settings → Diagnostic Buffer, because that read uses the operating-system interface rather than the project-image interface. Look for entries containing:

• Memory card removed/inserted
• MMC read error
• Flash error in load memory
• Corrupted block or Inconsistency in MMC

Any of these entries, combined with the matrix above, confirms MMC-level corruption.

Step 4 — Read the SZL System State List

From STEP 7, execute PLC → Diagnostics/Settings → System Information (or use a small script calling SFC 51 with SZL ID W#16#0131 and W#16#0132) and inspect:

MMC Card Verification

When the diagnostic matrix points at the MMC, validate the card with the following checks before declaring it scrap.

Visual Inspection

• Look for cracked solder joints at the connector fingers — common on cards that have been hot-plugged dozens of times.
• Inspect the alignment notch: an MMC inserted in reverse polarity (with a third-party adapter) will still fit but will not be detected; an MMC that has been bent may report present-and-faulty.
• Check for oxidation on the contact pads. A pencil eraser followed by isopropyl alcohol often restores a borderline card.

File-System Inspection

Insert the suspect MMC into a SIMATIC Field PG or a SIMATIC PC with an MMC reader. From a DOS prompt:

DIR <MMC-DRIVE>\S7_JOB\
DIR <MMC-DRIVE>\SIMATIC\
DIR <MMC-DRIVE>\FWUPDATE\

A healthy MMC contains at least the SIMATIC and S7_JOB directories. Missing directories or zero-byte files in SIMATIC indicate a corrupted FAT. The S7-300 MMC uses a 16-bit FAT (no subdirectories beyond the four Siemens-defined ones). Any deviation points to a defective card.

Test in a Reference CPU

Insert the suspect MMC into a known-good S7-313C-2 DP on the bench. Power up. The CPU should perform a RAM-to-MMC consistency check. If the SF LED lights solid and the diagnostic buffer reports Memory card fault, the MMC is unrecoverable.

Encryption Check

Siemens S7-300 MMC files can be encrypted with one of the following mechanisms:

• Know-how protection on individual blocks (OB, FB, FC, DB) — set with STEP 7 in the block properties. Encrypted blocks upload only as a placeholder stub; this is not the root cause of 33:17106.
• CPU password (read/write/insert/remove protection) — set in PLC → Access Protection. The CPU will reject a Read-Online request without the password, but it will not raise 33:17106; it will raise a different dialog ("Access to the object is denied").
• SIMATIC Logon / MMC encryption (only available on S7-31x PN/DP and S7-1500 with newer firmware, not on the S7-313). The S7-313 CPU family does not support MMC-level encryption, so encryption can be ruled out as a cause of the failure.

Because the S7-313 cannot encrypt the MMC, the answer to the recurring question "What if the MMC is encrypted?" is: in the S7-313 product line, MMC encryption is not a feature. If the same MMC behaves as defective across multiple CPUs, the card has a hardware fault, not an encryption state.

MPI Communication Settings

Once the MMC is replaced, lock in the MPI parameters to prevent recurrence. Recommended values for a small S7-300 station with one CPU and one PG:

STEP 7 Configuration Checks

Three configuration paths must be aligned. Mismatches here produce exactly the same 33:17106 dialog as an MMC fault, so verify them after the MMC swap to make sure the new card is not masking a configuration issue.

Path 1 — PG/PC Interface

From Start → SIMATIC → STEP 7 → Set PG/PC Interface:

• Access Point of the Application: S7ONLINE
• Interface Parameter Assignment Used: PC Adapter (MPI) -> USB

Path 2 — Accessible Nodes

From SIMATIC Manager → PLC → Accessible Nodes the CPU must appear with its MPI address. If it does not, the bus is the problem, not the MMC.

Path 3 — Online View

From SIMATIC Manager → View → Online the project tree of the running CPU should mirror the offline tree. If it does not, the new MMC has not yet been written by the CPU's RAM-to-MMC copy, or it contains a project that the online view cannot reconcile with the offline view in STEP 7.

Step-by-Step Resolution

1. Power down the S7-313. Open the front cover, depress the MMC ejector, and remove the card. Place it in an antistatic bag and label it "DO NOT REUSE — TEST ONLY".
2. Insert a known-good MMC of equal or larger size. For an S7-313, the smallest card Siemens ships is the 64 KB 6ES7 953-8LF11-0AA0. Newer cards in the 6ES7 953-8Lxxx-0AA0 family (up to 8 MB) are fully backward-compatible.
3. Power up the CPU. The CPU will boot from RAM (the project is mirrored in work memory) and will mark the new MMC as unformatted. The SF LED will be off; the RUN LED may flash once and go solid green.
4. Connect STEP 7 with the PC Adapter and PLC → Accessible Nodes. The CPU should appear.
5. Download the project to the new MMC: PLC → Download User Program to Memory Card. STEP 7 writes the entire project image to the MMC.
6. MRES the CPU if you want a fully clean state: place the mode switch in MRES, hold for ~3 s until the STOP LED blinks, release, push again within 1 s, hold for ~3 s. The CPU erases work memory and reloads from the new MMC.
7. Verify by reading the diagnostic buffer. It should contain a single entry Restart (cold start) initiated by user with timestamp 0.
8. Mark the suspect MMC for RMA or destruction. Even if the card passes a one-time read, its flash wear is non-uniform and the failure will recur.

Verification Procedure

After the resolution, run the following acceptance checks. The machine must be in a safe state; the checks are read-only.

1. Accessible Nodes returns the CPU with correct MPI address.
2. Upload (PLC → Upload Station to PG) succeeds without error.
3. Compare Online / Offline shows no differences (or only the expected time-stamp differences in OB1 / OB35).
4. Diagnostic buffer shows no MMC-related entries since the swap.
5. Monitor / Modify of a known tag (e.g., a marker in MB10) returns a current value.
6. Cycle time on PLC → Module Information → Scan Cycle Time is within ±10 % of the design value.

Related Error Codes

Official Siemens References

The Siemens support database contains the canonical root-cause notes for this family of errors. The most directly relevant entries are:

• Siemens FAQ 19215608 — "Why is it not possible to upload to the PG?"
• Siemens FAQ 26123822 — "S7-300/S7-400: Communication problems between PG and CPU"
• Siemens FAQ 10420976 — "MPI parameter settings for the S7-300"

FAQ