L6470PD - motor speed vs. clock setting

[Central SUPPORT]

We are using L6470PD driver IC for driving 2-phase stepping motor. Problem is related to external clock and internal clock setting in L6470.

1. In fact, we noticed different motor rotation speed when we switch between external clock of 16MHz and internal clock of 16MHz generated by OSC. We realized that motor rotation number in using external clock is slower x 0.666 than using internal clock in 16MHz clock. This is an important aspect of our application where we have to use internal and external clock with exactly same resulting motor speed.
2. By the way, is there any method of changing motor speed without changing SPEED parameters?

NOTE: This question and answer originated from a customer support case which was handled by us. We regularly review support cases and add any helpful ones here for all to benefit from.

[Central SUPPORT]

1. Reported difference between internal and external clock behavior is unusual. Please check directly the internal oscillator precision monitoring the OSCOUT pin (EXT_CLK='1' & OSC_SEL='011' in the CONFIG register). In any case, before changing clock source configuration, a hardware reset is mandatory. Switching to different clock configurations during operation may cause unexpected behavior.
2. The only way to change the motor rotation speed is acting on SPEED parameters.