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I have gone through the DRV8849 datasheet and I have doubts regarding the initial position mentioned in that.
As per the datasheet :
"The initial excitation state is an electrical angle of 45°, corresponding to 71% of full-scale current in both coils. This state is entered after power-up, after exiting logic undervoltage lockout, or after exiting sleep mode"
Does this driver rotate( mechanically rotate) the stepper motor to a default stage after every power reset ?
Take an example that the driver was pointing to 180 degree and if reboot happens It will come to angle 45 degree automatically and rotate the motor(Mechanically) to a default position?
This startup condition is commonly used in stepper drivers. This is the electrical angle of the coil current or known as phase angle not the stepper rotor position angle. When energized in this manner, the stepper locks on to the nearest magnetic pole step that corresponds to this electrical angle of excitation. Depending on the motor's rotor position there may or man not be any motion felt. Often times it may just be a fraction of a step or a single step at the most. The stepper generates maximum hold torque with both coils energized. No, the driver will not rotate the stepper if its indexer was reset.
If you'd want to drive the motor to it's home position after reboot irrespective of previous position then you must use the external microcontroller to determine the home usually sensed with a microswitch or optical or hall sensors for end point sensing. Alternatively you could use a stepper driver from our portfolio that supports stall detection. Example devices DRV8434S, DRV8434A, DRV8461, DRV8462, DRV8452.. A stall will be detected when the motor is driven to the end points. Based on the mechanical design of your application you should device a simple algorithm to determine the home position. You may be able to find several examples when you perform a web search for "finding home position in stepper motor drives" or similar search text. I hope this helps.
So we have to go for microswitch or hall sensor option to detect end point because in out mechanical setup there won't be any stopper, It will be 360 degree continuous rotation. That is why stall detection will not happen.
