TMC428_06 Datasheet, PDF (4/58 Pages) List of Unclassifed Manufacturers – Intelligent Triple Stepper Motor Controller with Serial Peripheral Interfaces

TMC428 DATASHEET (v. 2.02 / April 26^th, 2006)
4
SS
µC
CLK
MOSI
SCK
MISO
nSCS_C
SDI_C
REF1 REF2 REF3
TMC428-PI24 /
TMC428-DI20
nSCS3
nSCS2
nSCS_S
SDO_S
SCK_C
SCK_S
SDO_C _{CLK V33 V5 V5 TEST GND GND} SDI_S
470 nF
Note: output SDO_C will
nerver be high impedance
+5 V
nSCS
SDI
Driver
w/o SDO
SCK
10K
SM#3
nSCS
SDI
Driver
w/o SDO
SCK
SM#2
nSCS
SDI
Driver ^SDO
w/o SDO
SCK
SM#1
Figure 2-2: Usage of drivers without serial data output (SDO) with TMC428 in larger packages
(*the DI20 package variant is not recommended for new designs)
2.1 Step Frequencies
The maximum SPI^TM data rate is the clock frequency divided by 16. The maximum step frequency
depends on the total length of the datagrams sent to the SPI^TM stepper motor driver chain. At a clock
frequency of 16 MHz, with a daisy chain of three SPI^TM stepper motor drivers of 16 bit datagram length
each, the maximum full step frequency is 16 MHz / 16 / ( 3 * 16 ). This is approximately 20 kHz and
that is much higher than needed for typical stepper motors. But, the micro step rate may be higher,
even if the stepper motor driver does not see all micro steps due to SPI^TM data rate limit, as long as the
number of skipped micro steps is less than a full step. In this respect, one should remember, that at
high step rates– respectively pulse rates –the differences between micro stepping and full step
excitation vanishes.
2.2 Modes of Motion
The TMC428 has four different modes of motion, programmable individually for each stepper motor,
named RAMPMODE, SOFTMODE, VELOCITYMODE, and HOLDMODE. For positioning applications
the RAMPMODE is most suitable, whereas for constant velocity applications the VELOCITYMODE is.
In RAMPMODE, the user just sets the position and the TMC428 calculates a trapezoidal velocity profile
and drives autonomously to the target position. During motion, the position may be altered arbitrarily.
The SOFTMODE is similar to the RAMPMODE, but the decrease of the velocity during deceleration is
done with a soft, exponentially shaped velocity profile. In VELOCITYMODE, a target velocity is set by
the user and the TMC428 takes into account user defined limits of velocity and acceleration. In
HOLDMODE, the user sets target velocities, but the TMC428 ignores any limits of velocity and
acceleration, to realize arbitrary velocity profiles, controlled completely by the user. The TMC428 has
capabilities to generate interrupts depending on different stepper motor conditions chosen by an
interrupt mask. However, status bits sent back automatically to the microcontroller each time it sends
data to the TMC428 are sufficient for polling techniques.
The TMC428 provides different modes for reference switch handling. In the default reference switch
mode, the three reference switch inputs (REF1, REF2, REF3) are defined as left side reference
switches, one for each stepper motor. In another mode, the 1^st reference input (REF1) is defined as left
reference switch input of motor number one, the 2^nd reference input (REF2) is defined as left reference
switch input of motor number two, and the 3^rd reference input (REF3) is defined as right reference
switch of stepper motor number one. In that mode, there is no reference switch input available for
stepper motor three. With an external multiplexer 74HC157 any stepper motor may have a left and a
right reference switch.
Many serial stepper motor drivers provide different status bits (driver active, inactive, ...) and error bits
(short to ground, wire open, ...). To have access to those error bits, datagrams with a total length up to
48 bits sent back from the stepper motor driver chain to the TMC428 are buffered within two 24 bit
wide registers. The microcontroller has direct access to these registers. Although, the TMC428
provides datagrams with up to 64 bits, only the last 48 bits sent back from the driver chain are buffered
for read out by the microcontroller. This is because buffering of 3 times 16 bits is sufficient for a chain
of three stepper motor drivers (see Figure 2-1, page 3) and most other drivers sending back up to 16
bits. For a chain of three TMC236 / TMC239 / TMC246 / TMC249 all status bits are accessible. From
Copyright © 2004-2006, TRINAMIC Motion Control GmbH & Co. KG