Compiler: DAC8718 can't be used

Tool/software: TI C/C++ Compiler

Hello, I am testing DAC8718.

I want to use unipolar mode to let DAC offer 8-way adjustable output., and I offer AVDD = 32V, AVSS = 0V, VREF = 5V, IOVDD = DVDD = 5V, gain=6. But I got a problem that DAC outputs offset voltage(about 8V) whatever I want it to output.

I don't know if the problem is on a solid-state circuit or a program driver. Can you point out where the problem is or provide a driver for me to refer to?

Thanks for reading.