Siemens 810D Alarm 120202 MMC Waiting for Communication Partners

Problem Overview

The Siemens Sinumerik 810D control with MMC100.2 HMI boots, services load, and then the operator screen displays "MMC100.2 version 05.03.31 Waiting for communicationpartners". The boot is interrupted before ShopMill can render, leaving the panel effectively black. Alarm 120202 "Wait for connection to NC/PLC" is raised in parallel. The fault usually appears immediately after the on-board lithium cells (NCK battery and CMOS battery on the MMC/PCU) are replaced on an aged machine such as a Hardinge VMC, Fadal 4525, or similar 3-axis vertical machining center equipped with the 810D powerline or 810D CCU3 architecture.

The condition is recoverable in most cases. The HMI process is alive and able to render the Siemens Services, Diagnostics, and Start-up areas if the operator repeatedly cycles the Machine area key, which proves the underlying link from the CCU to the NCK/PLC is at least partially intact. The boot halt is a startup-ordering problem, not a fatal link failure.

Observed Symptoms

Root Cause Analysis

Alarm 120202 in Sinumerik 810D/840D is raised by the HMI when the HMI-MMC (or the modern PCU/TCU equivalent) cannot complete the OPC-style or NCVAR.INI-driven handshake with the NCK and PLC within the configured timeout. The default timeout window on MMC100.2 software version 05.03.31 is short (typically 30-60 s after the last Services-area phase). Three root-cause families dominate field reports:

1. NCK / PLC data loss after battery replacement. With dead batteries, the persistent NCK machine data, PLC retentive flags, and the licensed option set (CF card slot on the NCU) may not survive a power-down. The NCK boots into an "empty" machine configuration and asks the HMI for commissioning data that no longer exists.
2. HMI application dino failed init-complete handshake. dino is the display initialization component of the MMC HMI. A failure here means the HMI never marks the link ready, so the NCK times out trying to confirm the partner is present.
3. MMC vs. NCU software / version mismatch. The unit may be a MMC102 (despite the silk-screen label) running a software set that does not match the boot sector the NCK expects. Cross-flashed or partial image restoration commonly produces this exact symptom.

The most common contributor is a partial or failed general reset (NC + PLC clear) on the NCU. A clean reset is the prerequisite for the HMI to re-initialise the link and for the on-board archives to be reloaded successfully.

Pre-Procedure Verification

Before clearing the NC or PLC, confirm the following so the reset does not lock the machine out of recoverable data:

1. Archive the on-board images. From Start-up → Series Commissioning → Create Service Commissioning Archive, copy the active NC and PLC archives to an external PG/PC over Ethernet or to a PC card. Files of interest: *.ARC in /user/sinumerik/hmi/data/ and PLC project *.dp in the PLC area.
2. Image the MMC drive. If the MMC is a PCU 50 / PCU 50.3 or an MMC100.2 with a CompactFlash or HDD, connect a USB or Ethernet and create a sector image. Tools: WinSCP over the documented MMC IP, or a Linux dd image from a bootable MHI rescue stick.
3. Verify drive integrity. A chkdsk /f on every MMC partition must return clean. Bad blocks on the partition holding mmc2.exe or the registry will mimic a communication-partner fault even when the NCU is fine.
4. Identify the NCU variant. Open the cabinet and read the NCU label. 6FC5410-0AY03-0AA0 is a 810D CCU3. 6FC5410-0AY01-0AA0 is an earlier 810D. The switch positions below are valid for both, but the LED colour mapping (PS / PF / PR) is identical.
5. Identify the HMI module. Confirm whether the unit is MMC100.2 (CPU 586, 32 MB RAM, 4 MB Flash) or MMC102 (StrongARM, 64 MB RAM, 16 MB Flash). The image and the licence are tied to the module, not just to the disk.

NC and PLC General Reset (Reference Procedure)

The Sinumerik 810D / 840D NCU uses a 4-position rotary switch S4 and a 2-position mode switch S3 on the front of the NCU. The PS (Power Supply) and PR (PLC Run) LEDs above the 7-segment display report state. Use the following reference sequence for a full NC + PLC clear.

PLC General Reset

1. Set S3 on the NCU to position 1.
2. Power on the control. Wait for the 7-segment to show a stable number.
3. When the control is fully powered up, press the Reset pushbutton on the NCU front.
4. Wait for the NCU display to show 6.
5. Set S3 to 0 and press Reset.
6. Wait for the NCU display to show 6 again.
7. Turn S4 to position 2 — PS LED is ON.
8. Turn S4 to position 3 — PS LED is OFF.
9. When the PS LED comes on, turn S4 to position 2 then immediately back to position 3.
10. PS LED should now be blinking at ~2 Hz. This is the PLC clear-in-progress state.
11. Set S4 to position 0 — PR LED should become solid green within a few seconds.
12. If the PR LED does not light solid green, the procedure was not performed correctly. Repeat PLC steps 1 through 4 (with the 0 → 1 → 0 transitions) before retrying the S4 sequence.

NC General Reset

1. Set S4 to position 2.
2. Press Reset on the NCU.
3. Wait for the 7-segment to step through 1, 2, ..., 6 and to land on 6 with the PF (Power Fail / PLC Fault) LED OFF.
4. Power-cycle the control.
5. On reboot, the HMI should now be able to complete the communication handshake and either drop into Start-up mode or boot ShopMill directly.

Recovering the Original MHI Environment

If the active Windows / MHI image will not boot, the MMC 100.2/102 carries a hidden Original MHI Environment partition with a baseline HMI. Booting from it is the fastest path to a working display, but it is password-protected.

If none of the above work, the password hash is stored in \mhi\system\hmi.ini and can be cleared by editing the registry hive HMI under SOFTWARE\Siemens\SINUMERIK with a regedit offline mount from a Linux rescue environment. A direct edit of mhisetup.ini on the Original MHI partition with a new Password= entry and re-seal is documented for field service on the 810D.

Reloading the On-Board Archives

1. After a successful NC + PLC clear, the HMI will boot to either the Start-up area or directly into ShopMill / ShopTurn, depending on configuration.
2. From the active HMI, navigate to Start-up → Archive → Read In.
3. Select the on-board NC archive (*.ARC) from /card/user/sinumerik/hmi/data/archive/ or from the same path on the internal HDD.
4. Read in the NC archive, then the PLC archive, in that order. Acknowledge all popups.
5. Power-cycle the control. The next boot should reach the operator screen without alarm 120202.

MMC100.2 vs MMC102 - Identify Before You Reflash

Verification Checklist

Run the following checks after the procedure to confirm the fix is complete and stable:

1. Alarm 120202 is no longer present in the alarm log at next boot. Verify under Diagnostics → Alarm Log.
2. ShopMill loads fully without the "dino didn't post initcomplete" warning.
3. Jog the spindle in manual mode at low RPM. NCK → HMI feedback must show the actual RPM without timeouts.
4. Run a dry-run NC program (e.g. G91 G00 X1.0) and confirm the active block display updates in real time.
5. Power-cycle the control three consecutive times. Each boot must reach the operator screen without the "Waiting for communicationpartners" banner.
6. Replace the NCK and CMOS batteries with fresh cells (e.g. Panasonic BR-2032 on the MMC, Tadiran TL-5104 on the NCU) and record the install date on the cabinet label.

Troubleshooting Matrix

Field-Proven Cautions

• Do not pull the NCK or CMOS battery while the control is energised. Loss of NCK memory mid-write can corrupt the licence on the CF card slot and require a Siemens re-licence procedure.
• Do not skip the S3 = 1 → S3 = 0 transition at the start of the PLC clear. Without it, the PS LED sequence will not behave as documented and the clear will not register.
• Do not power off the control during the "dino" init-complete phase. Power-loss here is the most common cause of needing to re-image the MMC entirely.
• The "Machine" key cycling workaround is for diagnostics only. It does not clear the alarm and the control will not run a part program until the HMI-NCK link is fully established.
• If the machine has a Hardinge, Fadal, or any third-party PLC project, the OEM-specific ladder logic must be reloaded from the OEM archive after a PLC general reset. A standard Siemens archive will not contain the custom PLC blocks.