TMC424-PI24 Trinamic Microchips, TMC424-PI24 Datasheet - Page 36

• Manufacturer Part Number: TMC424-PI24
• Description: Economic Miniature Three Axis Microstepping Stepper Motor Controller
• Manufacturer: Trinamic Microchips

TMC428 DATASHEET (V. 2.00 / November 12, 2003)
36
The control signals for each of the two coils of a 2-phase stepper motor are 6 bits for the DAC
controlling the current of a coil, a phase polarity bit, and a fast decay bit for those stepper motor driver
chips with a fast decay feature for the coil current. These signals are available individually for each coil
(COIL A and COIL B). Constant configuration bits named Zero and One are provided. Additionally,
step and direction bits are available. One unique 5 bit code word– named primary signal code –is
assigned to each primary control signal (see Table 11-1).
The microstep unit (including sequencer) provides the full set of control signals for three stepper motor
driver chips. A subset of these control signals is selected by the stepper motor driver datagram
configuration, which is stored within the first 32 addresses representing 64 values of the on-chip RAM
(see Table 10-1, page 34). The stepper motor drivers are organized in a daisy chain. So the
addressing of the stepper motor driver chips within the daisy chain is by its position.
As mentioned before, the TMC428 sends datagrams to the stepper motor driver chain on demand. To
guarantee the integrity of each datagram sent to the stepper motor driver chain, the status of all
primary control signals is buffered internally before sending. Afterwards, the transmission starts with
selection of the buffered primary control signals of the first motor (smda=%00) by reading the first
primary signal code word (even data word at on-chip RAM address %00000) from on-chip
configuration RAM area. The primary signal codes select the primary signals provided for the first
stepper motor. The first stepper motor is addressed until the NxM (next motor) bit is read from on-chip
configuration RAM. The stepper motor driver address is incremented with each NxM=’1’ as long as the
current stepper motor driver address is below the value set by the parameter LSMD (last stepper
motor driver). If the stepper motor driver address is equivalent to the LSMD parameter, a NxM=’1’
indicates the completion of the transmission. With that, the stepper motor driver address counter of the
serial interface is reinitialized to %00 and the unit waits for the next transmission request.
So, the order of primary signal codes in the on-chip RAM configuration area determines the order of
datagram bits for the stepper motor driver chain, whereas the prefixed NxM bit determines the stepper
motor driver positions. If no NxM bit with a value of ‘1’ is stored within the on-chip RAM, the TMC428
will send endlessly. So, the on-chip RAM has to be configured first. After power-on reset, the registers
of the TMC428 are initialized in a way, that no transmission of datagrams to the motor driver chain is
required. Access to on-chip RAM is always possible, also during transmission of datagrams to the
driver chain.
11.1 Initialization of on-chip-RAM by µC after power-on
All registers are initialized by the automatic power-on reset. The registers are initialized, and the
stepper motors are at rest. The on-chip RAM is not initialized by the power-on reset. Writing to
registers may involve action of the stepper motor units initiated by the TMC428 resulting in sending
datagrams to the stepper motor driver chain. Those datagrams have a random power-on configuration
of the on-chip-RAM. So, before trying to move a motor, the on-chip RAM must be initialized first.
11.2 An Example of a Stepper Motor Driver Datagram Configuration
The following example demonstrates, how to configure the datagram and shows what has to be stored
within the on-chip RAM to represent the desired configuration. That example refers to a driver chain of
three TRINAMIC stepper motor drivers of type TMC236, TMC239, TMC246, TMC249. From the
TMC428 datagram configuration point of view, there is no difference between these drivers. All these
drivers have a serial interface of 12 bits length. The configuration is as follows. For the first and the
second stepper motor driver of the chain the fast decay control bit (FD_A, FD_B) is fixed to ‘0’. For the
third driver the fast decay control bit are used. The corresponding content of the configuration on-chip
RAM is outlined in Table 11-2. The sequence to be sent to the TMC428 for this configuration is
outlined in Table 11-3.
Hint: The stepper motor driver datagram configuration can be accessed at any time without conflict,
e.g. to changed between a configuration using fast decay versus a configuration where fast decay is
disabled.
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