AN-693| Application Note

LM628 Programming Guide

National Semiconductor Application Note 693 Steven Hunt January 1999

Introduction
The LM628/LM629 are dedicated motion control processors. Both devices control DC and brushless DC servo motors, as well as, other servomechanisms that provide a quadrature incremental feedback signal. Block diagrams of typical LM628/LM629-based motor control systems are shown in Figures 1, 2. As indicated in the figures, the LM628/LM629 are bus peripherals; both devices must be programmed by a host processor. This application note is intended to present a concrete starting point for programmers of these precision motion controllers. It focuses on the development of short programs that test overall system functionality and lay the groundwork for more complex programs. It also presents a method for tuning the loop-compensation PID filter. (Note 1)

Reference System
Figure 15 is a detailed schematic of a closed-loop motor control system. All programs presented in this paper were developed using this system. For application of the programs in other LM628-based systems, changes in basic programming structure are not required, but modification of filter coefficients and trajectory parameters may be required.

I. Program Modules
Breaking programs for the LM628 into sets of functional blocks simplifies the programming process; each block executes a specific task. This section contains examples of the principal building blocks (modules) of programs for the LM628.

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FIGURE 1. LM628-Based Motor Control System

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FIGURE 2. LM629-Based Motor Control System
Note 1: For the remainder of this paper, all statements about the LM628 also apply to the LM629 unless otherwise noted.

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