Multiturn Overflow

If using a multiturn feedback where the machine period is not an integer divisor of the encoder period, the full turn count must be saved so that the exact position can be recovered after a power cycle. The machine period is the number of units required by the machine to complete one operational cycle. The encoder period is the maximum amount of travel measurable by the encoder. The encoder period is calculated using the following formula:

encoder period = 2(number of encoder turn bits)(units for one turn of an end system)(gear ratio)

In some applications, a multiturn feedback is not enough to ensure that the position is known after a power cycle. These applications are those where:

Machine period ≠ encoder period * N

In these cases, it is necessary to track and store the number of turn bits beyond the bits stored in the feedback. These bits can be stored by setting FB1.PMTSAVEEN = 1. The supported feedback types include all multiturn encoders: BiSS"Bi-directional Serial Synchronous interface" An open-source communication protocol for feedback devices. With BiSS, all of the computation for interpolation in regard to position occurs on the ASIC directly in the encoder, EnDat, HIPERFACE and Tamagawa (the algorithm requires at least 12 multiturn bits). If FB1.PMTSAVEEN is set to 1 on an invalid feedback type then an error will be reported and FB1.PMTSAVEEN will be set to 0.