Datasheet

TMC429 DATASHEET (v. 1.07 / 2012-AUG-01) 47

% 11 10010 0 00000000 00 110010 00 110001 : 50 & 49 : $E4003231

% 11 10011 0 00000000 00 110100 00 110011 : 52 & 51 : $E6003433

% 11 10100 0 00000000 00 110110 00 110101 : 54 & 53 : $E8003635

% 11 10101 0 00000000 00 111000 00 110111 : 56 & 55 : $EA003837

% 11 10110 0 00000000 00 111001 00 111000 : 57 & 56 : $EC003938

% 11 10111 0 00000000 00 111011 00 111010 : 59 & 58 : $EE003B3A

% 11 11000 0 00000000 00 111100 00 111011 : 60 & 59 : $F0003C3B

% 11 11001 0 00000000 00 111101 00 111100 : 61 & 60 : $F2003D3C

% 11 11010 0 00000000 00 111110 00 111101 : 62 & 61 : $F4003E3D

% 11 11011 0 00000000 00 111110 00 111110 : 62 & 62 : $F6003E3E

% 11 11100 0 00000000 00 111111 00 111111 : 63 & 63 : $F8003F3F

% 11 11101 0 00000000 00 111111 00 111111 : 63 & 63 : $FA003F3F

% 11 11110 0 00000000 00 111111 00 111111 : 63 & 63 : $FC003F3F

% 11 11111 0 00000000 00 111111 00 111111 : 63 & 63 : $FE003F3F

Table 13-2 – Datagrams for initialization of a quarter sine wave period microstep look-up-table

These 32 datagrams (Table 13-2) are sufficient for all programmable micro step resolutions. If micro

stepping is used for at least one stepper motor, these 32 datagrams have to be sent once to the

TMC429 for initialization of the micro step table after power-on reset. The initialization of the micro step

look-up-table is not necessary, if full stepping is used for all stepper motors. The on-chip RAM is not

initialized during power-on reset. So, the full initialization of the whole micro step look-up-table is

recommended to avoid trouble caused by missing look-up table entries. Additionally, a fully initialized

micro step look-up-table allows the selection of individual micro step resolutions for different steppes.

Hint: The previous section describes how to calculate values for the TMC429 sine wave look-up table,

and how to write those values into the look-up table RAM of the TMC429 via SPI datagramms.

Nevertheless, other formulas might generate sine wave look-up tables that better fit with respect to

equidistance of micro steps or concerning torque ripple. Alternatively, a sine wave look-up table based

y(i) = int[ 63 * sin(¼ * 2 *  * i / 64) ]

can be used. Even, adding some offset o within theoretical range from 0 to 63

y(i) = int[ o + (63-o) * sin(¼ * 2 *  * i / 64) ]

might enhance the micro step behavior together with mixed decay. Finally, a sine wave look-up table

has to be tested within the application and might need some fine adjustments for optimization.

13.1 Stepping through the Wave Look-Up-Table

The 64 values of the wave look-up table (LUT) hold a quarter period of a sine wave, indexed from 0 to

63. This quarter sine wave is expanded to full sine wave and full cosine wave by indexing the 64 values

of the LUT. The LUT index is mapped from a wave index of a full period from 0 to 255. The stepping

through the LUT is done with fixed increment width. The increment width is a power of two and it

depends on the micro step resolution selection usrs. The Table 13-4 gives the indices for the LUT for

the different micro step resolutions. For motion in positive direction, the full period index is incremented

from micro step to micro step. For motion into negative direction, the full period index is decremented

from micro step to micro step.

The sine is associated to phase A (PH_A) and the cosine is associated to phase B (PH_B). The phase

bits represent the sign of the sine resp. cosine function. The polarity of the phase bit (PH_A, PH_B)

and the polarity of the fast decay control bits (FD_A, FD_B) can be changed by the polarity bits within

the global stepper motor parameter register (see section 10.11, page 35).