Method and apparatus for multiplex control of a plurality of stepper

Abstract

A plurality of step time tables consisting of a sequence of step times defining intervals between steps and thus a velocity profile to be executed by a stepper motor are stored in a first memory. A step table defining a plurality of identical sequences of excitation pattern for driving a stepper motor is stored in a second table. Identical DMA channels output the step times to a timer and the plurality of exitation patterns to a buffer. The timer measures the duration of the step times and when each step time expires generates a trigger signal which initiates the transfer of the next step time and next excitation pattern through the respective DMA channels. The buffer includes a control register which selects one excitation pattern from the plurality of excitation patterns output from the step table to be output for control of a selected one of a plurality of motors connected to the buffer. The buffer outputs are inverted to form bipolar signals to drive current drivers in accordance with the excitation pattern. The apparatus is initialized by a data processor to select one of the plurality of excitation tables and to select one of the groups of outputs of the buffer to drive a corresponding selected motor. The DMA channel for outputting the step time table is initialized for non-repetitive operation and the DMA channel outputting the step table is initialized for cyclic operation. The direction in which the selected stepper motor is to be driven is determined by the direction in which the step table is accessed.