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Error Improvement Delta B Self Clocking Code

IP.com Disclosure Number: IPCOM000078321D
Original Publication Date: 1972-Dec-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 29K

Publishing Venue

IBM

Related People

Huth, HT: AUTHOR

Abstract

Self-clocking bar coded and magnetic coded data may be read and decoded by detecting transitions in the coded data and measuring the elapsed time between transitions with reference to a known reference, which precedes the data initially and thereafter with the next previously coded data element. The maximum error is a function of the shortest reference or data element measured. If T and 2T represent the extent of the data elements or references used in the code and E is the error factor then T+E over T-E = 2T+E over T+E and E = 1 over 5 T. Therefore, as long as E is less than 20% of T (the shortest element in the code) a correct decode will be made.

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Error Improvement Delta B Self Clocking Code

Self-clocking bar coded and magnetic coded data may be read and decoded by detecting transitions in the coded data and measuring the elapsed time between transitions with reference to a known reference, which precedes the data initially and thereafter with the next previously coded data element. The maximum error is a function of the shortest reference or data element measured. If T and 2T represent the extent of the data elements or references used in the code and E is the error factor then T+E over T-E = 2T+E over T+E and E = 1 over 5 T. Therefore, as long as E is less than 20% of T (the shortest element in the code) a correct decode will be made.

With codes such as F/2F and phase code, multiple transitions (two) sometimes occur. In F/2F. multiple transitions occur each time a "1" bit is encoded. In phase code, multiple transitions occur whenever a bit ("1" or "0") is followed by an identical bit. When a multiple transitions occurs, the normal reference available is reduced by a factor of two.

The circuit illustrated detects a multiple transition and generates a reference equal to the sum of the adjacent multiple transition, thus increasing the smallest reference available by a factor of two and thus achieving a 42.5% increase in error tolerance when the measurement technique described is used.

In the drawing, analog-to-digital wave shaper provides pulse signals coincident with the transition in the coded data. These are applied to three counters and a compare and control circuit. A source of clock pulses is connected to the counters which count the clock pulses under control of the compare and control circuit. Assuming that counter 1 has a count corresponding to a two unit reference stored in it at a transiti...