TMC428_06 Datasheet, PDF (22/58 Pages) List of Unclassifed Manufacturers – Intelligent Triple Stepper Motor Controller with Serial Peripheral Interfaces

TMC428 DATASHEET (v. 2.02 / April 26^th, 2006)
22
resolution microstepping, overshooting of one micro step is negligible in most applications. To avoid
overshooting, use pmul-1 instead of the selected pmul or select a pair (pmul, pdiv) with q = 0.95. The
first given source code example ‘pmulpdiv.c’ showing programming in C language based on this brute
force approach. Some conversions of the base present equations help to reduce the calculation effort
drastically.
8.11.1 Optimized Calculation of p_mul and p_div
With the equations above, one can simplify the calculation of the parameters pmul and pdiv using the
expression
pmul = p * 2^3 * 2^pdiv – 128
with
p = a_max / ( 128 * 2^( pulse_div – ramp_div ) ).
To avoid overshooting, use
p_reduced = p * ( 1 – p_reduction[%])
with p_reduction approximately 5% instead of unreduced p. With this, one gets
pmul = p_reduced * 2^3 * 2^pdiv – 128 = 0.95 * p * 2^3 * 2^pdiv – 128.
With this, pmul becomes a function of the parameter pdiv. To find a valid pair {pmul, pdiv} one just
has to choose that pair {pmul, pdiv} out of 14 pairs for pdiv = {0, 1, 2, 3, ..., 13} with pmul within the
valid range 0 ≤ pmul ≤ 127. An example ‘pmulpdiv.c’ showing programming in C language can be
found on page 53. This source code can directly be copied from the PDF datasheet file.
8.12 lp & ref_conf & ramp_mode (rm) (IDX=%1010)
The bit called lp (latched position) is a read only status bit. The configuration words ref_conf and
ramp_mode are accessed via a common address, because these parameters normally are initialized
only once. The configuration bits ref_conf select the behavior of the reference switches, while the two
bits ramp_mode (rm) select one of the four possible stepping modes.
ramp_mode
%00
%01
%10
%11
mode
RAMP_MODE
SOFT_MODE
VELOCITY_MODE
HOLD_MODE
function
default mode for positioning applications with trapezoidal ramp
similar to RAMP_MODE, but with soft target position approaching
mode for velocity control applications, change of velocities with linear ramps
velocity is controlled by the microcontroller, motion parameter limits are ignored
Table 8-3 - Outline of TMC428 motion modes
The mode called RAMP_MODE is provided as the default mode for positioning tasks, while the
VELOCITY_MODE is for applications, where stepper motors have to be driven precisely with constant
velocity. The SOFT_MODE is similar to the standard RAMP_MODE except that the target position is
approached exponentially reduced velocity. This feature can be useful for applications where vibrations
at the target position have to be minimized. The HOLD_MODE is provided for motion control
applications, where the ramp generation is completely controlled by the microcontroller.
The TMC428 has three reference switch inputs REF1, REF2, REF3. Without additional hardware,
three reference switches are available. These switches can be used as reference switches and can be
Copyright © 2004-2006, TRINAMIC Motion Control GmbH & Co. KG