Cyclic redundancy check (CRC) is an error detection byte that detects communication errors to and from the host and ADC. CRC is the division remainder of the payload data by the prescribed CRC polynomial. The payload data are 1, 2, 3, or 4 bytes depending on the data transfer operation.

The host computes the CRC over the two command bytes and appends the CRC to the command string (third byte). A fourth, zero-value byte completes the command field to the ADC. The ADC performs the CRC calculation and compares the result to the CRC transmitted by the host. If the host and ADC CRC values match, the command executes and the ADC responds by transmitting the valid CRC during the fourth byte of the command. If the CRC is error free and the operation is a data read, the ADC responds with a second CRC that is computed for the requested data byte payload. The response data payload is 1, 3, or 4 bytes depending on the type of operation.

If the host and ADC CRC values do not match, the command does not execute and the ADC responds with an inverted CRC value, calculated over the received command bytes. The inverted CRC is intended to signal the host of the failed operation. The host terminates transmission of further bytes to stop the command operation. The CRC1 bit is set in the STATUS0 register when an error pertaining to ADC commands occurs. The STAT12 and CRC2 flags are set when an error pertaining to PGA register access occurs.

The ADC is ready to accept the next command after all required bytes are transmitted when no CRC error occurs, or after a CRC error occurs when terminated at the end of the fourth command byte.

The CRC data byte is the 8-bit remainder of the bitwise exclusive-OR (XOR) of the argument by a CRC polynomial. The CRC polynomial is based on the CRC-8-ATM (HEC) polynomial: X⁸ + X² + X + 1. The nine binary polynomial coefficients are 100000111b. The following sections detail the input and output data of each command.

See the example C code for the CRC calculation in the ADS125H02 Example C Code software. Also see the ADS125H02 Design Calculator software to calculate specific CRC code values.

In the command descriptions from the Section 9.5.5 section, these CRC mnemonics apply:

• CRC-2: Input CRC of command byte 1 and command byte 2
• Out CRC-1: Output CRC of one register data byte
• Out CRC-2: Output CRC of two command bytes, inverted value if an input CRC error is detected
• Out CRC-3: Output CRC of three conversion data bytes
• Out CRC-4: Output CRC of three conversion data bytes plus the STATUS0 byte
• Echo Byte 1: Echo out of input byte 1
• Echo Byte 2: Echo out of input byte 2