What happened?
On the Prusa CORE One, communication with the xBuddy extension board is achieved using the MODBUS protocol. In MODBUS, there are two types of devices: the master and the slave, also known, respectively, as client and server. On Prusa CORE One firmware, the master is the xBuddy, and each slave is called puppy.
A fingerprint is a unique identifier of a specific version of the firmware. The Prusa CORE One checks the fingerprint of the puppies, to ensure the firmware flashed on the peripheral boards is compatible with the printer, and the boards are safe to use. In case this procedure does not occur in the correct time window, the printer will show the message: "Waiting for fingerprint timed out".
Error name: Puppy fingerprint timeout
Error code: #31521
The error indicates most likely a configuration problem that might have stemmed from the firmware, or a faulty connection of the xBuddy extension board.
How to fix it?
Access the xBuddy and xBuddy extension boards by loosening six M3x4bT bolts to remove the cover. Once visible, check the boards for visible damage on their surface, and check the connection between xBuddy and xBuddy extension for any irregularities.
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