TMC428 ETC-unknow, TMC428 Datasheet - Page 20

• 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)
To represent the parameter p = p_mul / p_div = (128+pmul) / 2^(3+pdiv) one just has to find a pair of
pmul and pdiv that approximates p, with pmul in range 0 ... 127 and pdiv one of {8, 16 , 32 ,64 ,128 ,
256, 512, 1024, 2048, 4096, 8192, 16384, 32786, 65536}. There are only 128 * 14 = 1792 pairs of
(pmul, pdiv). So, one can simply try all possible pairs (pmul, pdiv) with a program and choose one pair.
To find one pair, one has to calculate
and
and
for each pair (pmul , pdiv) and select one pair for that 1.0 < q < 0.95 is valid. So, the value q interpreted
as a function q(a_max, ramp_div, pulse_div, pmul, pdiv) gives the quality criterion required. Although
q = 1.0 indicates that (pmul , pdiv) perfectly represents the desired p for a given a_max, this could
cause overshooting because of finite numerical precision. In case of high resolution micro stepping,
overshooting of one micro step is negligible, if it is below the micro step resolution of a stepper motor. To
avoid overshooting, one can use pmul-1 instead of the selected pmul. An example program in C
language can be found on page 47.
lp & ref_conf & ramp_mode (rm) (IDX=%1010)
The bit vectors ref_conf and ramp_mode are accessed via a common address, because these parameters
normally are initialized only once. The bit called lp (latched position) is a read only status bit. The TMC428
has three reference switch inputs. Without additional hardware, three reference switches are available. Per
default, each reference switch input is assigned individually to each stepper motor as a left reference
switch. The reference switch input REF3 can alternatively be assigned as the right reference switch of
stepper motor number one. 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 (see Figure 11). The
additional hardware is just a 74HC157, where three of four 2-to-1-multiplexers are used. The feature of
multiplexing is controlled by the bit named refmux in the stepper motor global parameter register (rrs=1
& address=111111).
The two least significant bits on this address named ramp_mode (rm) select one of the four possible
stepping modes:
The mode called RAMP_MODE is proposed as the default mode for positioning tasks, where the
VELOCITY_MODE is the default 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 quite slowly, but this feature could be useful for those applications where
vibrations at the target positions have to be minimized. The HOLD_MODE is proposed for motion control
applications, where the ramp generation is completely controlled by the micro controller.
Copyright © 2000, TRINAMIC Microchips GmbH
TRINAMIC
M I C R O C H I P S
p = a_max / ( 128 * 2^( ramp_div-pulse_div ) )
p’ = p_mul / p_div = (128+pmul) / 2^(3+pdiv)
q = p / p’
00 : RAMP_MODE
01 : SOFT_MODE
10 : VELOCITY_MODE
11 : HOLD_MODE
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