| 摘要 |
<p>A CODED RECORD AND METHODS OF AND APPARATUS FOR ENCODING AND DECODING RECORDS A novel record with alternate width modulated bars and spaces is decoded by comparing the width of each bar or space with a pair of reference values based on the product and quotient of a constant and the width of another bar or space to establish bit value. When the width value is greater or less than the reference value, the bit value is established. When the width values lie between the reference values, a state of equality is established which is resolved into a bit value by reference to the results of a prior or subsequent comparison. A system embodying the method includes storage means for storing width values, reference registers for establishing successive different sets of product and quotient reference values, and comparators controlled by the stored width and reference values for establishing the greater and less than and equality status conditions. In one embodiment, a shift register and logic circuits controlled by the status conditions provide dynamic interpretation of the status conditions into code bits as the character is read. In another embodiment, the status conditions are stored and then translated into code bits after a complete character has been read. In one code set, each character code of seven bits formed by four bars and three spaces uses five bits to define the character and the remaining two bits to provide separate bar and space parity bits. This and the fact that only one space "1" and one bar "1" are included in a proper code results in a code with an extremely low expected rate of undetected error. The system also includes separate parity check circuits for the decoded bar and space bits.</p> |
