68300

Hi all,
I am using the Table Stepper Motor (TSM) function in the TPU to, 
well, run a stepper motor.  I am having two problems that I am hoping 
someone can help me solve.

First, I have some c-code to run the motor in an open-loop mode. 
Every 5mS I read the PRESENT_POSITION register, add an interger (say 
8), then write the result to DESIRED_POSITION. Then update the HSR to 
implement the command. My start rate is around 140 pulses per second 
(pps) and the slew rate is around 2135 pps.  I would expect the motor 
to run at a somewhat constant rate, or at least dither back and forth 
around the given rate based on the discrete acceleration rates in the 
profile lookup table. Instead it is very jerky doing stop and go type 
behavior. The pulse waveform out of the TPU shows both phases pulsing 
as expected, then one phase stops while the other phase keeps 
toggling a few times, then both phases begin pulsing again. This 
occurs somewhat rhythmically.

The second problem is the 1.8 degree per step motor will be rotating 
in the proper direction, suddenly reverse at a somewhat higher rate 
and travel more than one revolution, then reverse again and travel as 
normal. The phasing never changes to warrant the motor changing 
directions. I suspect the anomally above is causing the motor to have 
a resonance problem, but I have never heard of a motor traveling 
backwards for any substantial distance.

Can anyone help me with these problems?

Thanks,
Jeff