TMC428_06 Datasheet, PDF (16/58 Pages) List of Unclassifed Manufacturers – Intelligent Triple Stepper Motor Controller with Serial Peripheral Interfaces

TMC428 DATASHEET (v. 2.02 / April 26^th, 2006)
16
8 Register Description
The registers hold binary coded numbers. Some are unsigned (positive) numbers, some are signed
numbers in two’s complement, and some are control bits or single flags. The functionality of different
registers depends on the ramp mode (s. page 22).
8.1 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 TMC428 moves the stepper motor in that direction
of x_target so that the difference becomes zero. The condition | x_target - x_actual | < 2²³ 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 TMC428 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.
8.2 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.
8.3 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 26 for details) and
depends on the clock frequency of the TMC428.
v(t)
v_max
v_min
a_max
∆v
t₀
∆t₀₁
t₁
acceleration
constant velocity
- _{a_max}
a_max
∆v
- _{a_max}
t
t₂
t₃ t₄
t₅
∆t₅₆
t₆
t₇ t₈
deceleration
acceleration deceleration
Figure 8-1: Velocity ramp parameters and velocity profiles
Copyright © 2004-2006, TRINAMIC Motion Control GmbH & Co. KG