Single width bar code with end code providing bidirectionality

摘要

A single width bar code is appended with an end mark which includes a blank interval and a bar. The resulting bar code is bidirectional and inherently self clocking so as to be particularly useful in the identification of semiconductor wafers in very large scale integrated circuit manufacturing processes. The codes described are robust, reliable, and highly readable even in the face of relatively high variations in scanning speed. The codes are also desirably dense in terms of character representations per linear measurements, an important consideration in semiconductor manufacturing wherein space on chips and wafers is at a premium. Additionally, a preferred embodiment of the present invention exhibits a minimum number for the maximum number of spaces between adjacent bars in code symbol sequences.