TMC428_06 Datasheet, PDF(44/58 Page) List of Unclassifed Manufacturers – Intelligent Triple Stepper Motor Controller with Serial Peripheral Interfaces

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TMC428_06 Datasheet, PDF (44/58 Pages) List of Unclassifed Manufacturers – Intelligent Triple Stepper Motor Controller with Serial Peripheral Interfaces

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TMC428 DATASHEET (v. 2.02 / April 26th, 2006)

The shape parameter Ï selects one of three functions fbox(Ï), fcircle(Ï), frhomb(Ï), respectively a

superposition of two of them. The shape parameter Ï = 0 selects the function fcircle(Ï) which is the sine

function sin(Ï ) as used for sine cosine microstepping. With this, one gets the unit circle (r=1.0) by

transformation to Cartesian coordinates {y = sin(Ï ); x = cos(Ï )} as outlined in Figure 12-1, a shape

parameter Ï = +1.0 results in a box, and a shape parameter Ï = -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 (radians) ranging from (0 â¤ Ï < 2Ï ) are used for the description.

The three functions for superposition controlled by the shape parameter Ï are

fbox (Ï )

ï£±

ï£´ï£´ï£²Ï

ï£´

â2

âÏ

ï£´ï£³ 2

â¤

â¥

fcircle (Ï ) = sin(Ï )

fr hom b (Ï )

âÏ

All together, these three functions are combined to form the function

ï£± f (Ï) + Ï â[ f (Ï) â f (Ï)]

f (Ï)

ï£´ï£´

fï£²

ï£´

f f f ï£´ï£³

circle

(Ï )

circle

(Ï ) + Ï â[

circle

box

circle

(Ï ) â

(Ï )]

circle

r hom b

for

Ï >0

Ï =0

Ï <0

So, the shape parameter Ï 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 Ï by

downloading different micro step tables on-the-fly into the TMC428 during motion of a stepper motor.

For calculation of data for the micro step look-up table of the TMC428, one has to replace ÏâÏi

ranging from 0 to Ï /2 for the quarter period by

Ïi

with i = {0,1,2,3,...,63} .

The amplitude of the shape function fÏ (Ïi) 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.

13 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 TMC428 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 â Getting Started" together with

C source code examples are available on www.trinamic.com

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