Hi Karen
1. Should I read angle register when the phase voltage zero crossing event occurred? Or it doesn't matter.
hmani: It doesn't matter. The angle register updates only after getting the two necessary zero-crossings (negative to positive transitions) needed for the measurement. So, you need not worry about reading any bad values in-between.
2. Upon the data sheet, for the angle register, 1 LSB presents 3.90625 us. It is independent from the line voltage frequency, is it righ?
hmani: Yes. But based on the line frequency, the angle resolution will vary (as per datasheet- page 33 Rev.B)
3. Can I change the ANGLESEL bits setting dynamically (any time) during the operation? Or must reset the ADE7880 chip after the change? If I could, is there any settling time after the change?
hmani: No reset required. After you change the ANGLESEL bits, wait for the first zero-crossing to occur on both signals being sensed (as per the new setting) and then read the ANGLEx register.
Regards
hmani