Increment-decrement logic for serial printer

Abstract

A serial printer comprises a carriage, a print member rotatably mounted to the carriage and including a plurality of character elements, a drive coupled to the print member for rotating the print member to a desired rotational position, a device coupled to the print member for generating a plurality of periodic position signals each indicative of the rotational movement of the print member, and a device for storing a count indicative of the actual rotational position of the print member, the device for storing including a device responsive to an increment pulse for incrementing the count by one and a device responsive to a decrement pulse for decrementing the count by one. An increment-decrement device is coupled to the device for generating and is responsive to the position signals for generating an increment pulse at a predetermined point during the period of a predetermined one of the position signals during rotation of the print member in one direction and a decrement pulse at said predetermined point during rotation of the print member in the opposite direction. The increment-decrement device includes a device for inhibiting the generation of a predetermined increment pulse that would normally occur when the print member has been rotated too far and overshoots the desired rotational position by a predetermined amount and then is returned to the desired rotational position. The printer further includes a device responsive to the count and to a signal representative of the desired rotational position of the print member for controlling the direction and speed of rotation of the print member.