Browse Prior Art Database

Markers in Run Length Limited Codes

IP.com Disclosure Number: IPCOM000073623D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Lewis, DM: AUTHOR

Abstract

Run-length-limited codes have been used to limit the bandwidth of a data channel. Each run-length-limited code has rules for maintaining the run-length limit. For example, in a data channel having NRZ signals, the number of zeros in a row (i.e., cell positions without a change in signal state) may be limited to two. In such a situation, maximum number of zeros permissible in the data code group at either end is one. This permits joining two code groups, each having a zero at the end and maintaining the run-length limit of two. It is desired to generate special marker signals which are identifiable and which do not violate the run-length limit of the code.

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 3

Markers in Run Length Limited Codes

Run-length-limited codes have been used to limit the bandwidth of a data channel. Each run-length-limited code has rules for maintaining the run-length limit. For example, in a data channel having NRZ signals, the number of zeros in a row (i.e., cell positions without a change in signal state) may be limited to two. In such a situation, maximum number of zeros permissible in the data code group at either end is one. This permits joining two code groups, each having a zero at the end and maintaining the run-length limit of two. It is desired to generate special marker signals which are identifiable and which do not violate the run-length limit of the code. These markers are preferably arranged symmetrically such that when the data channel includes a magnetic media, reading the media in either direction of motion results in the same signal pattern for the marker signals.

Examples of special marks usable in run-length-limited codes are shown below for a five bit code group. Marks reading from the left which may be adjacent a data code group or another marker group are: 11100

10100

01100.

A similar set of special code groups which violate the coding rules but which maintain the run-length limit for reading from right to left: 00101

00110

00111.

Another special code group could be all 1's. Yet another one which may be used in the center of a special code group is: 00100.

A distinguishing characteristic of these marks is that the run...