The MMC (PCU) has a configuration file that tells it where to look for the NCK. If this file is corrupt or reset to defaults, it will look at the wrong address.
"It’s stuck in a loop," Elias muttered, gesturing to the screen. "I’ve cycled the power thrice. Checked the cables. The PLC status LEDs are green, but the HMI just won't bridge the gap." sinumerik 810d waiting for nck connection
The display should count up from 0 to 6 (or A to F depending on firmware) and settle on a steady green "6" (or "0" or "8" – consult your manual). If it freezes on "1" or "4", the NCK is halted in hardware initialization. The MMC (PCU) has a configuration file that