TMC389 Datasheet, PDF (19/48 Pages) TRINAMIC Motion Control GmbH & Co. KG. – three phase stepper motor driver

TMC389 DATASHEET (V. 1.15 / 2015-OCT-27)
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figure 7: internal microstep table showing the first quarter of the sine wave
7.3 Switching between different microstep resolutions
In principle, the microstep resolution can be changed at any time. The microstep resolution determines
the increment respectively the decrement, the TMC389 uses for advancing in the microstep table. At
maximum resolution, it advances one step for each step pulse. At half resolution, it advances two
steps and so on. This way, a change of resolution is possible transparently at each time. However, you
may experience the motor behavior becoming direction dependant, when switching microstep
resolutions. This behavior results from table sampling points not evenly shifted inside the microstep
table with respect to the step width. To avoid this, always switch to a lower resolution, when the actual
microstep position is a multiple of the desired table step width. This is always satisfied at position zero
in the microstep table.
7.4 Step rate multiplier and stand still detection
The step rate multiplier can be enabled by setting the INTPOL bit. It supports a 16 microstep setting
and Step/Dir mode, only. In this setting, each step impulse at the input causes the execution of 16
times 1/256 microsteps. The step rate for the 16 microsteps is determined by measuring the time
interval of the previous step pulses and dividing it into 16 equal parts. This way, a smooth motor
movement like in 256 microstep resolution is achieved. The maximum time between two microsteps
corresponds to 2^20 i.e. roughly one million clock cycles, in order to reach evenly distributed 1/256
sine wave steps. At 16MHz clock frequency, this results in a minimum step input frequency of 16Hz for
step rate multiplier operation, i.e. one and a half motor fullsteps per second. A lower step rate causes
the stand still flag to become set as soon as the time is expired. Execution of microsteps will happen
with a frequency of 1/(2^16) clock frequency.
Copyright © 2010 TRINAMIC Motion Control GmbH & Co. KG