Datasheet

TMC429 DATASHEET (v. 1.07 / 2012-AUG-01) 26
Copyright © 2010-2012, TRINAMIC Motion Control GmbH & Co. KG
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 TMC429 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
used as automatic stop switches as well. Per default, one reference switch input is assigned
individually to each stepper motor as a left reference switch (see Figure 10-4, page 37). The reference
switch input REF3 can alternatively be assigned as the right reference switch of stepper motor number
one (see Figure 10-5, page 37). In that configuration a left and a right reference switch is assigned to
stepper motor one, a left reference switch is assigned to stepper motor two, and no reference switch is
assigned to stepper motor three. The bit named mot1r in the stepper motor global parameter register
(rrs=1 & address=%111111) selects one of these configurations. With additional hardware, up to six
reference switches a left and a right one assigned to each stepper motor are supported. The
additional hardware is just a 74HC157, where three of four 2-to-1-multiplexers are used (see Figure
10-7, page 38). The feature of multiplexing is controlled by the bit named refmux in the stepper motor
global parameter register (rrs=1 & address=111111).
A reference switch can be used as an automatic stop switch. The reference switch indicates the
reference position within a given tolerance. The automatic stop function of the switches can be enabled
or disabled. Also a reference tolerance range (see register dx_ref_tolerance, page 30) can be
programmed, to allow motion within the reference switch active range during reference point search.
When a reference switch is triggered, the actual position can be stored automatically. This allows
precise determination of the reference point. This is initiated by writing a dummy value to register
x_latched (see page 30). The read-only status bit lp (latch position waiting) then indicates that the next
change of the selected reference switch will trigger latching the position x_actual. The lp bit is
automatically reset after position latching.
negative direction
mechanical inaccuracy of switches
(switching hysteresis)
x
1
x
2
motor
traveller
left switch
x
left
dx_ref_tolerance
positive direction
x
3
x
4
x
right
right switch
x
traveler
Figure 9-4: Left switch and right switch for reference search and automatic stop function
ref_conf mnemonic
Function
DISABLE_STOP_L
0 :
Stops a motor if velocity is negative (v_actual < 0) and the left reference switch becomes
active.
1 :
Left reference switch is disabled as a an automatic stop switch.
DISABLE_STOP_R
0 :
Stops a motor if velocity is positive (v_actual > 0) and the right reference switch becomes
active.
1 :
Right reference switch is disabled as an automatic stop switch.
SOFT_STOP
0 :
Stopping takes place immediately, motion parameter limits are ignored.
1 :
Stopping takes place in consideration of motion parameter limits, stops with linear ramp.
REF_RnL
0 :
The left reference switch controls reference switch functions.
1 :
The right (not left) reference switch controls reference switch functions.
lp
0 :
This is the power-on default of the lp (latched position waiting) bit.
1 :
x_latched has been initialized by a write access to latch the position on a change of the
reference switch. 
Table 9-4: Reference switch configuration bits (ref_conf)