Code 235-007B: Unknown device on SPI bus (%1)
Issue Description & Safety Warning
The Heidenhain TNC Series CNC has triggered a critical Unknown device on SPI bus (%1) alarm. Immediate attention from a qualified operator or maintenance technician is required to prevent secondary damage to the equipment or spoiled parts during the manufacturing cycle. Always ensure standard safety and LOTO procedures are followed before accessing electrical cabinets.
Official Troubleshooting Steps
[Cause of error] The NC software identifies every connected devices by means of a device table. The table indicates whether the device is supported by the software version installed on the control. A device that the software does not support or that is not yet entered in the device table is connected with the SPI bus. The device concerned is indicated in the additional information. [Error correction] - Inform your service agency. - Run an update of the NC software if the device is not supported by the currently installed version of NC software. - Update the device table. A new device that is not yet listed in the device table might be supported by the installed software. In this case an update of the device table is required. [598] 10/2023
Source: HEIDENHAIN NC Error Messages — TNC7/640/620/320/128, CNC PILOT 640, MANUALplus 620 (10/2023)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Heidenhain TNC Series CNC Alarms
Heidenhain controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code 235-007B on the TNC Series CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Heidenhain's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 4497 Heidenhain TNC Series CNC codes.
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