SF_CRC_INIT

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.

The SF_CRC_INIT function initializes the CRC calculation table and does further settings for the used safety communication CRC calculation identified via input CRC_SLOT.

This function shall only be called once per safety communication and related CRC slot because:

Internal tables are created for optimized runtime calculation which needs processing time.
Further calls (after successful configuration) return FALSE and re-configuration is rejected because the former successful initialization remains unchanged, as designed.

The function SF_CRC_INIT must be called for each used safety communication identified via CRC_SLOT input.

Table 1097: FB name: SF_CRC_INIT
Name	Data type	Initial value	Description, parameter values
VAR_INPUT
CRC_SLOT	BYTE	0	Identifies the CRC for the given safety communication with related CRC slot value for which the CRC initialization is configured. Allowed values: 0..7
BITS	BYTE	0	Defines the CRC bit size to be used (depending on degree of the used polynomial). Allowed values: 8 … 32
START_VALUE	DWORD	16#00000000	Defines the start value for CRC calculation. It depends on the safety communication protocol specification. All values are allowed.
POLYNOM	DWORD	16#00000000	CRC polynomial (represented by the hexadecimal value of the given CRC equation). All values except 0 are allowed. 0 value leads to SAFE STOP of the safety CPU if SF_CRC_FINISH function is called afterwards.
REFLECT_IN	BOOL	FALSE	Defines if input data shall be rotated bitwise or not. FALSE: No bitwise rotation TRUE: Bitwise rotation
REFLECT_OUT	BOOL	FALSE	Defines if CRC value shall be rotated bitwise or not FALSE: No bitwise rotation TRUE: Bitwise rotation
XOR_OUT	DWORD	16#00000000	Defines the operand for bitwise XOR operation with the CRC value, which is later delivered at the output using SF_CRC_FINISH function. All values are allowed.
VAR_OUTPUT
SF_CRC_INIT	BOOL	TRUE	Result of CRC calculation initialization for safety communication and related CRC slot. TRUE: CRC calculation initialization is successful. FALSE: Error in CRC calculation initialization. Possible reasons: CRC_SLOT invalid (> 7) BITS invalid (not in range 8 … 32) CRC_SLOT already successfully initialized.

Call in ST

SF_CRC_INIT_Slot1 := SF_CRC_INIT(CRC_SLOT1,
                            BITS_SLOT1,
                            START_VALUE_SLOT1,
                            POLYNOM_SLOT1,
                            REFLECT_IN_SLOT1,
                            REFLECT_OUT_SLOT1,
                            XOR_OUT_SLOT1);