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6 Control communication
The control frame
The control frame enables the protected and confirmed reading and writing of the register of a slave and the
protected and confirmed sending of commands to the slave. The control frame results from a count of BiSS
frames generating and transmitting sensor data.
The register access or the command is always carried out at the end of the cycle of the last DCM bit, i.e. with
the expiration of the BiSS timeout in the slave. The control frame can be canceled at any time with the
transmission of 14 “0“ bits. The start bit of a control frame must be preceded by at least 14 cycles with
CDM = “0“.
CRC checking
Control communication also uses a checksum for transmission checking. The CRC polynomial used is the
same as in protected SCD data transmission:
X^(6) + X^(1) + 1
With it, 6 CRC bits are available which are transmitted inverted. Calculation is carried out with the starting
value zero via the addressing sequence or the data bits beginning with the most significant bit, always
excluding the start bit.
Note: Before each control frame at least 14 bits with CDM=“0“ must be transmitted.