I am driving a simple stepper motor in my application at 100% torque. To reduce heat and wear, I dial back TRQ to 25% between motor movements.
When I drive the motor normally, everything seems fine. However, if I attempt to issue a single pulse to the driver (in any step/microstep mode) the motor doesn't step! I did notice though, that if I issue 2 pulses, the motor successfully moves each time. (This is true in each step mode) Furthermore, when I completely remove the code that sets the 25% holding torque, single-pulse movements work as expected.
Finally, I probed my STEP pin and triggered a capture on the falling edge of TRQ0 (setting torque from 25% to 100%). I measured 10µs between the falling-edge of TRQ0 and the rising-edge of STEP. There are no timing requirements in the datasheet regarding the TRQ pins, however. But perhaps TRQ isn't meant to be used like this or there is actually a setup time required before stepping?
I actually have three motors in my system, all driven with 8880s, using almost identical code (so I know it's not a firmware issue). The other two motors are set to TRQ 25% for 100% of the time and the issue does not arise at all. They are able to move using single pulses.
Has anyone seen anything like this?