Clarification of Serial control with Position feedback

The documentation for the SMC03A is a bit sketchy. In fact, it has been marked as preliminary for several years now.

What I would like to clarify is precisely how the serial commands drive the unit in Position Feedback mode:

  • Does the “motor speed” parameter, 0 thru 7F, actually correspond to the position from 0 volts feedback to 5 volts feedback?
  • What effect does the direction bit have on the behavior?

In reading the doc for the newer SMC04, there is the potential for more resolution by using the 4 byte code. Does the direction bit behave the same way with the SMC04?

Bill Grant

Hi, Bill.

Yeah, the documentation is pretty bad. The speed command corresponds to a position command when in analog feedback mode. One direction gives you positions above 2.5V, and the other direction gives you positions under 2.5V, with higher speed commands corresponding to positions toward the extremes. Thus, with one direction bit and seven speed bits, you get 8-bit position resolution. The regular interface is the same on the SMC04, but that unit also has a higher-resolution 10-bit option.

- Jan