Datasheet
TMC429 DATASHEET (v. 1.07 / 2012-AUG-01) 19
Copyright © 2010-2012, TRINAMIC Motion Control GmbH & Co. KG
9 Register Description
The registers hold binary coded numbers. Some are unsigned (positive) numbers, some are signed
ent, and some are control bits or single flags. The functionality of different
registers depends on the ramp mode (s. page 25).
9.1 x_target (IDX=%0000)
This register holds the current target position in units of full steps, respectively micro steps. The unit of
the target position depends on the setting of the associated micro step resolution register usrs. If the
difference x_target – x_actual is unequal zero, the TMC429 moves the stepper motor in that direction
of x_target so that the difference becomes zero. The condition | x_target – x_actual | < 2
23
must be
satisfied for motion into the correct direction. Both, target position x_target and current position
x_actual may be altered on the fly. Usually x_target is modified to start a positioning. To move from
one position to another, the ramp generator of TMC429 automatically generates ramp profiles in
consideration of the velocity limits v_min and v_max and acceleration limit a_max.
Note: The registers x_target, x_actual, v_min, v_max, and a_max are initialized with zero after
power up. Thus, no step pulses are generated because motion is prohibited.
9.2 x_actual (IDX=%0001)
The current position of each stepper motor is available by read out of the registers called x_actual.
The actual position can be overwritten by the microcontroller. This feature is for reference switch
position calibration under control of the microcontroller.
9.3 v_min (IDX=%0010)
This register holds the absolute value of the velocity at or below which the stepper motor can be
stopped abruptly. The parameter v_min is relevant only for deceleration while reaching a target
position. It should be set greater than zero. This control value allows to reach the target position faster
because the stepper motor is not slowed down below v_min before the target is reached. Also
consider, that due to the finite numerical representation of integral relations, the target position can not
be reached exactly, if the calculated velocity is less than one, before the target is reached. So, setting
v_min to at least one assures reaching each target position exactly. The unit of velocity parameters
(v_max, v_target, and v_actual) is steps per time unit. The scale of velocity parameters (v_min,
v_max, v_target, v_actual) is defined by the parameter pulse_div (see page 29 for details) and
depends on the clock frequency of the TMC429.
v_max
t
v(t)
t
0
t
1
a_max
v_min
t
3
t
4
t
2
v
t
7
t
8
t
5
v
a_max
- a_max
- a_max
t
6
acceleration constant velocity deceleration acceleration deceleration
t
01
t
56
Figure 9-1: Velocity ramp parameters and velocity profiles