Datasheet
TMC429 DATASHEET (v. 1.07 / 2012-AUG-01) 50
Copyright © 2010-2012, TRINAMIC Motion Control GmbH & Co. KG
The shape parameter σ selects one of three functions f
box
(φ), f
circle
(φ), f
rhomb
(φ), respectively a
superposition of two of them. The shape parameter σ = 0 selects the function f
circle
(φ) which is the sine
function sin(
) as used for sine cosine microstepping. With this, one gets the unit circle (r=1.0) by
transformation to Cartesian coordinates {y = sin(
); x = cos(
)} as outlined in Figure 13-1, a shape
parameter σ = +1.0 results in a box, and a shape parameter σ = -1.0 results in a rhomb. Other values
except those, result in something between box and circle respectively something between circle an
rhomb.
The data values y(i) of the look-up table range from 0 to 63 and the argument I ranges also from 0 to
63. In the following, natural angles (ra
< 2
) are used for the description.
The three functions for superposition controlled by the shape parameter σ are
2
)(
)sin()(
4
2
1
4
0
2
4
)(
hombr
circle
box
f
f
if
if
f
All together, these three functions are combined to form the function
0
0
0
)]()([)(
)(
)]()([)(
)(
hom
for
for
for
fff
f
fff
f
brcirclecircle
circle
circleboxcircle
So, the shape parameter σ selects the type of function and it also provides a continuous transition
between circle and box respectively circle and rhomb. To estimate, what function would be best for a
given type of stepper motor, one can try microstepping based on different shape parameters σ by
downloading different micro step tables on-the-fly into the TMC429 during motion of a stepper motor.
For calculation of data for the micro step look-up table of the TMC429, one has to replace
I
ranging from 0 to
/2 for the quarter period by
}63,...,3,2,1,0{
642
iwith
i
i
.
The amplitude of the shape function f
σ
(φ
i
) has to be limited to the range of 0.0 to 1.0 respectively to the
range of 0 to 63 for the on-chip RAM as described in the beginning of the microstepping section.
14 How to get Started in Running a Motor
First of all, the Stepper Motor Driver Datagram Configuration has to be written into its RAM area.
Additionally, the Microstep Look-Up-Table has to be initialized when using microstepping. The
parameter LSMD, that is part of the global parameter register, has to be initialized. After that, the
parameters v_min, v_max, and the clock pre-dividers pulse_div and ramp_div and the micro step
resolution usrs has to be set. Then, a_max together with a valid pair of pmul and pdiv has to be set.
The switch configuration ref_conf together with the ramp mode rm has to be chosen. The reference
switch inputs REF1, REF2, REF3 should be pulled down to ground or disabled by setting ref_conf.
With those settings, the TMC429 runs a motor if one writes either x_target or v_target, depending on
the choice of the ramp mode rm. An application note named TMC428 Getting Started together with
C source code examples are available on www.trinamic.com