When I observed the voltage waveform of VT, I found that no matter how to modify the value of VT register, the waveform did not change. During the period, I have changed the DATA[1] of (0X0C) to 1 or the DATA[0] of (0X0D) to 1, and the value of RCV has also been changed. But VT is always 0. What I can be sure of is that the registers read and write values correctly, and that VDUT0 behaves correctly when setting VH and VL. The screenshot below is the value of VDUT0 that I measured while setting the values of different registers.