DRV8818: ENABLEn and RESETn together connection

Hi Michel,

When the RESETn signal is asserted and released (high to low to high), the indexer is reset to 45 degrees electrical angle (Table 2 Home state).

If you have stopped the stepper at any location other than the home state, the motor could move 1 to 2 full steps when reset.

For the reason above, may I suggest we focus on the loss of one step first?

After the full rotation of 200 steps, what changes are made to the STEP, RESETn, and ENABLEn signals?
What is the timing between the three signals?
Is there any load on the stepper motor that could cause the motor to move when the outputs are disabled (RESETn low, or ENABLEn high)?

Hi Rick,

The RESETn signal is activated only just  after the power up of the board ,  after, this signal RESETn   is always high.

The ENABLEn   is activated 49 ms before the STEP signal  (and RESETn is always high)

Today, the only way to avoid  to lose a step  is to activate simultaneously  ENABLEn  and RESETn (connection between the  two signals with an inverter 74HC14)

Thanks a lot for your velocity to answer

Michel  Thiébaut

Hi Michel,

Thank you for the images. This has not been reported previously.

By lose a step, do you mean the motor is one step short of 360 degree mechanical rotation?

Are you changing DIR after setting RESETn high?

Please note there is a HOMEn pin (it is open drain and requires a pullup) that helps determine the indexer position. If you started at the HOMEn position after releasing the reset, the HOMEn position should appear after 200 full steps.

Please check the HOMEn pin after RESETn is released. If it is not at the HOMEn position, this could be part of the reason.
 

Hi Rick,

Sorry for my delayed answer, I was absent the day before yesterday.

I send you graphs with the signals RESETn and ENABLEn  (connection  between the 2 signals with an inverter)  --> the stepper motor works correctly: no lose of steps  

So, at the beginning of a new rotation ,  ENABLEn goes low  and  RESETn goes  high  about 9 ns after  (74HCT04 propagation delay: tpd), at the end of the rotation ENABLEn goes high and  RESETn goes  low

Is it correct for you?

Thanks in advance for your answer

Michel Thiébaut

END of the rotation

Hi Michel,

What is the opto detection signal?

I cannot determine if this is correct. If at all possible, a scope capture of the STEP input and the HOMEn signal to count the number of HOMEn pulses and confirm the nHOME is at the same location at the end of 200 steps would help.

A scope capture of the current in one winding also helps.

Hi Rick

The following test was made with a connection between RESETn and ENABLEn via an inverter 

I send you a graph with HOMEn signal, we count  50 falling edges  ( 50 x 4 states in full step = 200 steps)

The optical detection is the signal coming from an optical switch .

The locating pin,  fixed on the axis of the stepper motor,  cut or not the IR beam of the optical switch

So, I am able to confirm that the time between the rising edge of OPTO DETECTION and STEP signal does not vary, even after 100   full rotations

Best Regards

Michel Thiébaut

Hi Rick,

Thanks for you  answer 

I also noted  that "having STEP high when releasing RESETn is considered the first rising edge"

Thanks a lot for your reactivity

Michel Thiébaut