GUI Application
6
SLVUBR6A – October 2019 – Revised October 2019
Copyright © 2019, Texas Instruments Incorporated
DRV8899-Q1 EVM GUI User's Guide
3.3.1.1.2
Step Mode
Step Mode allows the user to move the stepper motor a configured number of steps. Stepper controls are
enabled only when the 'Motor Driver' control is enabled for example, DRVOFF pin is set to low. When the
‘Start Steps’ button is clicked, the motor starts spinning at the starting speed and accelerates at the rate
configured. When the number of steps is reached, the motor stops.
The acceleration and deceleration profiles work similarly as before, except when the deceleration routine
starts and when the motor stops are a function of the 'Steps to Stop' and deceleration rate parameters.
The configuration can be visualized in the graph embedded in the GUI. If the "Reciprocate" button is
enabled, the stepper will travel the set number of steps, then reverse direction. It will do this continuously
until 'Stop Steps' is clicked.
shows the controls available in Step Mode
Figure 6. Controls for Step Mode
The parameters from 'Speed Mode' are reused as well, and they operate the same as described in
. Two new parameters have been added to properly control the limited number of steps
actuation. These parameters are described as follows:
Number of Steps —
This parameter is the number of steps that the controller will issue.
Steps to Stop —
The controller is continuously monitoring the step being issued and when the current
step is equal to the 'Steps to Stop' parameter, a deceleration profile is issued. If the value of the
'Steps to Stop' parameter is larger than the number of steps, then the motor stops abruptly and
without undergoing a deceleration profile.
When a deceleration profile is issued, the controller decreases the speed until reaching the 'Stopping
Speed' value. If the 'Number of Steps' parameter is met before the deceleration profile is complete, then
the motor stops at the current speed. If the stopping speed is met before all the number of steps is issued,
then the motor rotates at the stopping speed value until all the steps are executed.
Ideally, the system should resemble the case in which the controller executes all the commanded steps at
a speed as close as possible to the stop speed. In the event this is not possible because of the particular
parameters that were selected, stopping the motor at a speed very close to the 'Stopping Speed'
parameter is often good enough to ensure good motion quality and application performance.
shows the three conditions possible when stopping and the action taken.