TMC428 ETC-unknow, TMC428 Datasheet - Page 16

• Manufacturer Part Number: TMC428
• Description: Intelligent Triple Stepper Motor Controller With Serial Peripheral Interfaces
• Manufacturer: ETC-unknow

TMC428 DATA SHEET (V. 1.00 / February 12, 2001)
v_max (IDX=%0011)
This is the limit of the velocity. The absolute value of velocity– which may be positive or negative –will not
exceed this limit, except the limit is changed during motion to a value below the current velocity. Note: To
set target position x_target and current position x_actual to an equivalent value (e.g. to set both to zero
at a reference point), the assigned stepper motor should be stopped first, and the parameter v_max
should be set to zero to hold the assigned stepper motor at rest before writing into the register x_target
and x_actual.
v_target (IDX=%0100)
In modes RAMP_MODE and SOFT_MODE this register holds the current target velocity calculated internally
by the ramp generator. In mode VELOCITY_MODE a target velocity can be written into this register. Then
the associated stepper motor accelerates until it reaches the target velocity specified. Changing velocity
occurs in consideration of motion parameter limits in VELOCITY_MODE. In HOLD_MODE the register can
be overwritten but it is ignored.
v_actual (IDX=%0101)
This read only register holds the current velocity of the associated stepper motor. Internally, the ramp
generator of the TMC428 processes with 20 bits while only 12 bits can be read out as v_actual. So, an
actual velocity of zero read out by the micro controller means that the current velocity is in an interval
between zero and one. Because of this, the actual velocity should not be used to detect a stop of a
stepper motor. For stop detection there is a dedicated bit within the interrupt register, which can simply
be read out by the micro processor or generate an interrupt. But, if one writes zero to register v_actual,
which is possible in HOLD_MODE only, the associated stepper motor stops immediately, because hidden
bits are set to zero with each write access to the register v_actual. In HOLD_MODE only, this register is a
read-write register. In HOLD_MODE, motion parameters are ignored and the micro controller has the full
control to generate a ramp. In that mode, the TMC428 only handles the micro stepping and datagram
generation for the associated stepper motor of the daisy chain.
a_max (IDX=%0110)
The maximum acceleration is defined by this register. The unit of the acceleration parameters (a_max,
a_actual, a_threshold) is change of velocity per time unit divided by 256. Note: In contrast to the time
unit of the velocity parameters defined by pulse_div, the time unit of the acceleration parameters is
defined by the parameter ramp_div (see page 22). The change of pulse frequencies expressed as change
of velocity per second also depends on the frequency of the clock signal at pin CLK of the TMC428.
a_actual (IDX=%0111)
The actual acceleration, which the TMC428 actually applies to a stepper motor can be read out by the
micro controller from this register for monitoring purposes. Internally, it is updated with each clock. The
actual acceleration is used to select scale factors for the coil currents. The returned value a_actual is the
smoothed internal acceleration. This smoothing avoids oscillations of the readout value. Thus the returned
a_actual values should not be used directly for high precision applications.
Copyright © 2000, TRINAMIC Microchips GmbH
TRINAMIC
M I C R O C H I P S
16
16