A4988 stepping without input at 50khz

I have an A4988 and wired it on a breadboard with using the minimal wiring diagram.
It is not connected to a microcontroller, instead i want to generate the steps with a push button.

My problem: the motor is only vibrating when i energize the circuit and wont react to step input.

Using my oscilloscope i found the driver is stepping at a very high frequency, while step and direction pins are pulled to ground via 1kOhm resistor:

Sorry for the bad quality, time interval is 20us (so output is repeating at 50khz) and voltage is 5V per segment.

The circuit is powered by a 12V switching power supply and 5V is generated with an 7805 regulator.
I am using capacitors at both 12V (100uF) and 5V (10nF) input.
Ouput current limit is set to 800mA.
The circuit only includes the minimal elements to use the A4988, including 2 coils (1.6 ohm and 3.1 ohm, inductance about 1-3 mH)

What can cause this and how do i fix it?


Could you post pictures that show all of your connections including where the two sides of your scope probe are attached? Could you also post a link to more information about your stepper motor? If you measure the VREF voltage what is it?