Code 208756: <location>CBC: Number of mapped bytes exceeded
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical <location>CBC: Number of mapped bytes exceeded 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: Drive object: A_INF, B_INF, CU_LINK, CU_S, HUB, S_INF, SERVO, TB30, TM15, TM15DI_DO, TM17, TM31, TM41, TM54F_MA, TM54F_SL, VECTOR Reaction: NONE Acknowledge: NONE Cause: The number of bytes of the mapped objects exceeds the telegram size for net data. A max. of 8 bytes is permissible. Remedy: Map fewer objects or objects with a smaller data type. See also: p8710, p8711, p8712, p8713, p8714, p8715, p8716, p8717, p8730, p8731, p8732, p8733, p8734, p8735, p8736, p8737
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 208756 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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