I believe this is a typo error as there is no AD5698 part. I think you are referring to either AD5696 or AD5694 which are almost identical when it comes to the digital communication.
When writing to the part, the microcontroller acts as the master…
AD5681R: Tiny 12-Bit SPI nanoDAC+, with ±1 LSB INL and 2 ppm/°C Reference
AD5682R: Tiny 14-Bit SPI nanoDAC+, with ±2 LSB INL and 2 ppm/°C Reference
AD5683: Tiny 16-Bit SPI nanoDAC+, with ±2 (16-Bit) LSB INL
Q1. What is new?
A1. The nanoDAC+(TM) family offers improved analog performance in terms of INL and glitch energy specifications.. Some members of the family, those with a part number ending in 'R', for example AD5686R, include a low drift…