Motor phasing error

I have a machine that is giving me and motor phasing error on one motor intermittintly. This is a Umac with Geodrives using halls for phasing. What are the causes of a phase error when the "$" command is given? Mark Miller

If you have Hall Sensors and those are used for phasing, when a $ command is sent to the addressed motor, PMAC will look at the register addressed by Ixx81 and read it based upon the instructions in Ixx91. The Ixx91, bit 23 high means PMAC should handle the register pointed in Ixx81 as a hall sensor input. Meaning it expects the hall data to be on bits 20(W), 21(V), 22(U) and 23(T). Ixx91, bit 22 is the direction of Halls and whether it matches the direction of on-going phase position sensor. Ixx91, bits 16 to 21, defines the offset between the zero of the phase and the zero of Hall sensor defined as V crossing when U is Low. The only time on a Hall sensor setup, you would get a phase search error is when you have all high U:1, V:1 and W:1 or all low U:0, V:0 and W:0 which means either there is a problem with your wiring or the sensor. Also, I have seen noise on hall sensor lines causing this problem. In 120-degree hall sensors, A combination of 111 or 000 is not possible and that's why you are getting an error.