Modified biphase modulation bar code printer

Abstract

In biphase operations where logic 1's are represented by a logic 0-1 code in a data stream which controls bar code printing, and logic 0's are represented by a logic 1-0 code, the invention involves altering to a logic 0-0 code in the stream each logic 1-0 code which follows a logic 0-1 code. In a more specific aspect, binary information signals are encoded for detection by a reading system effective within a bandwidth of bar densities. Such encoding is effected by sensing each bit time period of the binary information signal, and representing a logic one level occurring within a bit time period by inserting a logic one level in a trailing half of a corresponding bit time period of an encoded signal. If a logic zero level is sensed in a bit time period of the binary information signal after the detection of a logic one level in an immediately preceding bit time period, logic 0's are inserted in the leading and trailing halves of a corresponding bit time period of the encoded signal. Further, if a logic zero level is sensed in a bit time period of the binary information signal after a logic zero level is detected in the immediately preceding bit time period, a logic one is inserted in the leading half of a corresponding bit time period of the encoded signal. The foregoing steps are repeated for each bit time period of the binary information signal.