AN3208

Driving stepper motors using STM8A and STM8S microcontrollers

Doc ID 17411 Rev 1

9/19

4

Driving stepper motors using STM8A and

STM8S microcontrollers

This application solution makes use of a PWM current control technique. The stepper motor

is driven directly by PWMs, I/O pins and a 74HC/HCT244 buffer/driver (so the position of the

motor can be controlled with precision without any feedback mechanism) of an an STM8A or

STM8S microcontroller. Two ends of each motor winding are connected to one PWM and

one I/O line. TIM1 (16-bit advanced control timer) peripheral on the STM8A or STM8S

allows two independent PWM signals to be generated. The PWM signals have the same

frequency and are controlled by the counter clock period and the capture/compare register

values (TIM1_CCRxH and TIM1_CCRxL). For detailed information about TIM1, refer to the

STM8A and STM8S device datasheets. Figure 7 shows the functional block diagram of a

stepper motor, STM8A PWM and I/O signals, and an 74HC244 buffer.

Figure 7.

Functional block diagram

The stepper motor used in the current solution is the M-S motor X25.689 from Switec (see

Figure 8 and Figure 9). The main features are:

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1/3 ° resolution per step

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Low current consumption

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High speed (greater than 600 °/s)

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Can be driven directly by a microcontroller

The M-S motor has two types of movement:

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Rotor movement

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Pointer shaft movement

This motor is therefore a bipolar motor. It has four different wires which operate the motor in

both clockwise and anti-clockwise directions.