GUI Application
5
SLVUBR6A – October 2019 – Revised October 2019
Copyright © 2019, Texas Instruments Incorporated
DRV8899-Q1 EVM GUI User's Guide
3.3.1.1
Stepper Control Modes
The GUI allows the user to control the stepper motion profile in two modes – Speed Mode and Step Mode.
To toggle between the modes, use the toggle button at the top of the screen.
3.3.1.1.1
Speed Mode
Speed Mode allows the user to spin the stepper motor continuously at a desired speed. The user
configures the starting speed, stopping speed, acceleration rate, and target speed. Stepper controls are
enabled only when 'Motor Driver' control is enabled for example, DRVOFF pin is set to low. The ‘Start
Steps’ button is enabled only when ‘Driver Outputs' control is enabled for example, DRVOFF pin is set to
low. When the ‘Start Steps’ button is clicked, the motor begins spinning at the starting speed and
accelerates to the target speed according to the configured acceleration rate. The acceleration profile in
the microcontroller firmware accepts the starting-speed and target-speed PPS values and calculates the
appropriate PWM clock period to create the stepping signal on the STEP pin. When the ‘Start steps’
button is clicked, the PWM timer generates steps at a rate specified by the 'Starting Speed' PPS
parameter. When ‘Stop Steps’ is clicked, the motor starts decelerating at the ‘Acceleration Rate’
configured to reach the stopping speed and eventually stop. The configuration is visualized by the
embedded graph shown on the GUI screen (
When accelerating or decelerating, the PPS signal is adjusted every 32 ms based on the integer value of
PPSPS / 32 ms. Acceleration rates must be between 1 and 65,535 PPSPS. The step rate increases by
the calculated value until the target speed is reached.
The starting speed must be less than or equal to the target speed. If the starting speed and target speed
are equal, the EVM firmware will not perform an acceleration routine. The stopping speed must also be
less than or equal to the target speed. The target speed is limited to a range between 1 and 65,535 PPS.
The 'Start Steps' command computes how frequently automatic speed updates are issued and a second
timer is used to change the speed according to the programmed acceleration rate profile. Once clicked,
the motor will begin spinning according to the parameters set in the GUI.
When the target speed PPS value is reached, the acceleration profile ends, and the motor continues
running at the target speed until the 'Stop Steps' button is clicked. When the stepper is commanded to
stop, the controller performs the same actions as it did while accelerating, but in reverse order, to
decelerate until the stopping speed PPS value is reached. At this point, the motor fully stops.
Figure 5. Controls available for Speed Mode