Apparatus for reducing the number of undetected errors read along the length of a binary information bearing medium

摘要

An apparatus is described for reducing the number of undetected errors serially read along the length of a magnetic stripe containing binary information. The magnetic stripe is adhesively attached to a plastic card. A serial self-clocking data stream is developed from a manual magnetic stripe encoded card reader. The data stream comprises clock and data signals including a start signal, an end signal and a summation signal. A four-stage down counter counts a predetermined number of clock signals which occur in a predetermined portion of the stripe after the occurrence of the summation signal. State machine control circuitry delays the detection of the data signals occurring after the end signal for a predetermined time to prevent the detection of the summation signal. Control circuitry controls the down counter and provides a finish signal after the down counter has counted off the number of clock signals in the predetermined portion of the stripe. A first AND gate provides an error signal upon the occurrence of a data signal after the summation signal. A status latch is provided to indicate which one, the error signal or the finish signal, occurs first.