Code 201220: <location>CU: Bas clk cyc too low
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical <location>CU: Bas clk cyc too low 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
Message value: Parameter: %1 Drive object: All objects Reaction: NONE Acknowledge: IMMEDIATELY Cause: The parameter for the basic cloc k cycle is set too short for the number of connected drives. Fault value (r0949, interpret decimal): The fault value specifies the parameter involved. See also: r0110 (Basic sampling times) Remedy: - increase the basic clock cycle. - reduce the number of connected drives and start to re-commission the unit. See also: r0110 (Basic sampling times)
Source: SINUMERIK 840D sl / 840Di sl / SINAMICS S120 Diagnostics Manual (DAsl, 03/2009)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Siemens SINUMERIK 840D CNC Alarms
Siemens controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code 201220 on the SINUMERIK 840D CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Siemens's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 4014 Siemens SINUMERIK 840D CNC codes.
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