dl-breadcrumbs__homedl-breadcrumb-item__separatorAC500-S safety PLCdl-breadcrumb-item__separatorSafety user manual V1.3.2dl-breadcrumb-item__separatorConfiguration and programmingdl-breadcrumb-item__separator...dl-breadcrumb-item__separatorAC500-S librariesdl-breadcrumb-item__separatorSafetyExt2_LV110_AC500_V27.libdl-breadcrumb-item__separatorSpecific functions for user-defined CRC calculationdl-breadcrumb-item__separatorApplication guidelines
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Application guidelines

This is the web edition of the original ‎⮫ AC500-S safety user manual, version 1.3.2. This web edition is provided for quick reference only. The original safety user manual must be used to meet functional safety application requirements.

We recommend to follow the guidelines to prevent the risk of getting invalid CRC values or unwanted SAFE STOP of the safety CPU.

Preparation guideline

  • Analyze the safety communication protocol specification you want to realize. Define the configuration values which are needed to configure your CRC functionality. It affects all input values of SF_CRC_INIT function.

Implementation guideline

  • Make sure that you call SF_CRC_INIT only once and with a polynomial unequal to 0.

    Only if SF_CRC_INIT returns TRUE, allow subsequent calls of SF_CRC_INPUT and SF_CRC_FINSH.

  • Make sure that you call SF_CRC_INPUT/SF_CRC_FINISH with correct CRC_SLOT input.

  • Make sure that you call SF_CRC_INPUT within the allowed safety application memory space, e.g., by using ADR and SIZEOF functions.

  • Make sure that you call SF_CRC_FINISH exactly one time after completion of the CRC calculation for the given user data block, and before the next CRC calculation cycle.

  • Make sure that you always exclude the received CRC value from the CRC calculation, and validate the received CRC value against the calculated CRC value from SF_CRC_FINISH output. In the case of mismatch, reject the received data. Only accept data with successful CRC validation.