TMC428_06 Datasheet, PDF(34/58 Page) List of Unclassifed Manufacturers – Intelligent Triple Stepper Motor Controller with Serial Peripheral Interfaces

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TMC428_06 Datasheet, PDF (34/58 Pages) List of Unclassifed Manufacturers – Intelligent Triple Stepper Motor Controller with Serial Peripheral Interfaces

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TMC428 DATASHEET (v. 2.02 / April 26th, 2006)

negative direction

reference

switch

motor

traveller

dx1 x1 xref x2 dx2

xtraveler

xmax

mechanical inaccuracy of switches

(switching hysteresis)

positive direction

Figure 9-7: Reference search

dx_ref_tolerance

9.9 Reference Search

The goal of the reference search is to determine the position xref of a reference switch (see Figure

9-7). Due to mechanical inaccuracy of switches, the reference switch is active within a range x1 < xref <

x2, where x1 and x2 may vary. If the traveler is within the range x1 < xtraveler < x2 before reference

search, it is necessary to go outside this range, because the associated reference switch is active. A

dummy write access to x_latched initializes the position latch register. Then, with the traveler within

the range x2 < xtraveler < xmax and the initialized register x_latched, the position x2 can simply be

determined by motion with a target position x_target set to -xmax. When reaching the position x2, this

position is latched automatically. With stop switch enabled, the stepper motor automatically stops if the

position x2 is reached. Then, the dx_ref_tolerance has to be set, so that motion within the active

reference switch range x1 < xref < x2 is allowed and to move the traveler to a position xtraveler < x1 if

desired. Then the register x_latched has to be initialized again to latch the position x1 by a motion to a

target position xtraveler < x1. When the positions x1 and x2 are determined the reference position xref =

(x1 + x2 ) / 2 can be set. Finally, one should move to the target position x_target = xref and set x_target

:= 0 and x_actual := 0 when reached.

9.10 Simultanous Start of up to Three Stepper Motors

Starting stepper motors simultaneously can be acheved by sending successive datagrams starting the

stepper motors. If the delay between those datagrams is of the magnitude of some microseconds, the

stepper motors can be considered as started simultaneously. Feeding the reference switch signals

through or gates (see Figure 9-8) allows exact simultaneous start of the stepper motors under software

control.

hold

nSCS_C

74HC32

REF1 REF2 REF3

nSCS_S

74HC157

/EN

SEL1/ /0

< MUX

+VCC

REF2_RIGHT

REF2_LEFT

REF3_RIGHT

REF3_LEFT

REF1_LEFT

REF1_RIGHT

SDI_C

TMC428

SDO_S

SCK_C

SDO_C CLK

V33

SCK_S

V5 TEST GND SDI_S

Figure 9-8: Reference switch gateing for exact simultanous stepper motor start

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