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Read Time Pulse Selection Apparatus

IP.com Disclosure Number: IPCOM000097476D
Original Publication Date: 1962-Dec-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 4 page(s) / 70K

Publishing Venue

IBM

Related People

Harrison, AR: AUTHOR [+3]

Abstract

The apparatus is used in a system for reading binary bits from a magnetic medium, where there is the possibility of error in bit sampling operations. Such is introduced by drift in the read clock oscillator frequency and by phase distortion inherent in high density magnetic recording systems. Distortion of the type considered here is the shifting of time position of bits which have been recorded at regular intervals on a medium and are being read at a uniform rate. It is summarized as being a shift of a 1 bit away from an adjacent 1 bit and toward an adjacent 0 bit, but where the presence of bits of like value on either side of a bit under scrutiny causes no shift.

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Read Time Pulse Selection Apparatus

The apparatus is used in a system for reading binary bits from a magnetic medium, where there is the possibility of error in bit sampling operations. Such is introduced by drift in the read clock oscillator frequency and by phase distortion inherent in high density magnetic recording systems.

Distortion of the type considered here is the shifting of time position of bits which have been recorded at regular intervals on a medium and are being read at a uniform rate. It is summarized as being a shift of a 1 bit away from an adjacent 1 bit and toward an adjacent 0 bit, but where the presence of bits of like value on either side of a bit under scrutiny causes no shift.

This apparatus selects one of the four successive clock pulses A, B, C, and D for admission to output line 1. Signals on line 1 are used to step a ring counter (not shown). The latter, in turn, is used with other apparatus for assembling into eight bit characters binary information bits which have been read in serially occurring time positions. A sync bit occurs between the eighth bit position of each character and the first bit position of the next succeeding character. It is sensed along with character bits as the recording medium is scanned. Pulses A, B, C and D are produced at a rate such that a complete sequence of pulses occurs in the time position allotted to each character bit or sync bit. The apparatus is effective to admit the same clock pulse to line 1 throughout the sensing of bits of an entire character and repeats the selection operation upon the occurrence of each sync bit.

The A, B, C, or D pulse, so selected normally, is the one which occurs two pulse positions after the observed position of the sync bit and may be shifted one pulse position in either direction in order to compensate for the above-identified phase shift. In this manner, the pulses are put on line 1 to step the above- mentioned ring counter during the interval between successive character bits. For instance, where the sync bit following character has been detected at pulse time B and the value of the eighth bit in the character preceding the sync bit is a 1, D pulses normally are admitted to line 1. Depending on the value of the first bit of the next character, it is necessary to advance the stepping time, i.e., admit C pulses to line 1, or to leave choice of stepping times unchanged, i. e., to admit D pulses to line 1, if the first bit of the next succeeding character is a 0 or a 1, respectively.

It is assumed next that the selection of an A, B, C, or D pulse for admission to line 1 has been effected for a first, currently received character, and that one of timing triggers 10 has been set in the process of such selection. Consequently, the And conditioned by the trigger 10 which has been set admits the appropriate (selected) A, B, C or D pulse to output line 1 for use in assembling the bits of this first character.

The 0 or 1 value of the eighth bit...