Browse Prior Art Database

Mark Generation in 2,7 Code

IP.com Disclosure Number: IPCOM000044551D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Gardner, HJ: AUTHOR [+2]

Abstract

A special address mark is generated during a format or record update operation in a diskette drive. The marks are generated by modifying a run-length limited, variable-word length encoder. This allows illegal code words to be used as special marks. These marks are of such a nature as to never occur in the normal encoded data. The special marks are detected without disturbing the normal decode process. This technique is illustrated for a 2,7 run-length limited code. Fig. 1 illustrates the code assignment for the mark. It can be shown that the code words (00100000)(001000) will not occur in any combination of assigned code words or in any half byte variation. Such a mark identifier meets the 2,7 constraints (minimum two zeroes; maximum seven zeroes).

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 61% of the total text.

Page 1 of 2

Mark Generation in 2,7 Code

A special address mark is generated during a format or record update operation in a diskette drive. The marks are generated by modifying a run-length limited, variable-word length encoder. This allows illegal code words to be used as special marks. These marks are of such a nature as to never occur in the normal encoded data. The special marks are detected without disturbing the normal decode process. This technique is illustrated for a 2,7 run-length limited code. Fig. 1 illustrates the code assignment for the mark. It can be shown that the code words (00100000)(001000) will not occur in any combination of assigned code words or in any half byte variation. Such a mark identifier meets the 2,7 constraints (minimum two zeroes; maximum seven zeroes). The choice of this sequence for part of an address mark is arbitrary, with many other possible choices available. This marker sequence would be concatenated with, at least, two legal code words to distinguish between the different types of markers required to support various recorded track architectures in disk drives. The selected encoder implementation is shown in Fig. 2. There will be two code bits for every single data bit so outputs T0 and T1 from combinational logic 10 provide the resulting encoded data word. The input to logic 10 is the state of the latches 11 through 16 in the data encoder. Examination of the expression for T0 illustrates that the third term is active when encoding t...