DAC8501: Behavior when 23-bit data is input to the DAC8501E

Part Number: DAC8501

Tool/software:

I'd like to know about the DAC8501E.

When I input 23-bit data in with the CLK while sync is Low, and then return the sync signal to Hi,
Vout changes.(Unexpected behavior)

The data I input is 0 for the first 6 bits (xxxxxx on the datasheet),
PD1 and PD0 are both 0,
D23 is 0,
D22 to D1 are 1.

(Confirmed with an oscilloscope)

According to the datasheet, if the sync signal is returned to Hi before inputting 24 bits,
Vout is not supposed to change.

Please tell me how the DAC8501E's Vout behaves when only 23-bit data is input.