The no-operation command bytes are 00h and 00h. Use this command if no input command is desired. If the SPI CRC check is enabled, the CRC byte is required (byte 3), which is always D7h for bytes 00h and 00h. SDI can be held low during data readback, but in CRC mode the SPI_ERR flag is set, which blocks future register write operations. The SPI_ERR flag can be ignored while reading conversion data until the next register write operation. At that point, the SPI_ERR flag of the STATUS register must be manually cleared by writing 1b.