Method and system for overriding error correction

Details Method and system for overriding error correction Method and system for overriding error correction

1998-03-02

2001-10-30

Decady, Albert (Department: 2133)

Error detection/correction and fault detection/recovery

Pulse or data error handling

Digital data error correction

C714S756000, C380S001000, C341S106000, C341S058000, C341S059000, C360S040000

Reexamination Certificate

active

06311305

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to the disabling of error-correction on digital optical media, such as Compact Disc (CD), Compact Disc Read_only Memory (CD-ROM) and Digital Video Disc (DVD).
Digital optical media is well-known in the art and is utilized to store large amounts of digital data in digital form, such as audio data, video data, software data, or document data. Software and document data may be read and utilized by a computer from digital optical media, such as Compact Disc Read-Only Memory (CD-ROM). There are also widely-available players for reading data from digital optical media and using this data to reconstruct audio, visual, text, and audio-visual information. Such players include, but are not limited to, CD players, CD-ROM multi-media players, game-playing systems, and DVD-players, which can reproduce sound, images, and test from data stored on digital optical media. Some computers are also configured to duplicate the functionality of CD players, CD-ROM multi-media players, game-playing systems, and DVD-players.
Description of Prior Art Digital Optical Media
Digital optical media technology is established according to a series of international standards, all of which are incorporated herein by reference. For example, some common standards applicable to CD's include: the International Standards Organization (ISO) standard 9660 entitled “Information Processing—Volume and File Structure of CD-ROM for Information Interchange, ISO standard 13490-I”, the International Electrotechnique Commission (CEI-IEC) standard 908, also known as the “Red Book”, and ISO/IEC 10140, also known as the “Yellow Book”.
FIG. 1
is a cross-sectional schematic of a portion of the data surface of a digital optical medium. Referring briefly to
FIG. 1
, according to these standards, digital optical media has at least one layer of transparent refractive material
10
which has data recorded on one surface which is coated with a reflective material
12
, and covered with an optional protective layer
14
. Reflective material
12
, in combination with transparent refractive material
10
, produces transparent reflective layer
24
whose optical properties depend on the properties both of reflective material
12
and transparent refractive material
10
.
Reading Data from Digital Optical Media
In order to read the data written onto Digital Optical media, such as CD-ROM and DVD, the media is rotated at a precisely-controlled speed, and light from a laser is focused through the disc-shaped substrate into transparent reflective layer
24
from which it is reflected back to a detector which measures the intensity of the reflected light. During the recording or manufacturing process of the digital optical media, the optical properties of the layer
24
are physically modified according to the data to be recorded so that the reflected light will vary significantly in intensity depending on where the laser light strikes. Typically, there are two different intensity levels for the reflected light. A region
18
which reflects a high intensity of the laser light is referred to as “land”, and a region
20
which reflects a low intensity of light is referred to as “pit”. Pits and lands may be physically implemented in different ways, but they always have the property of reflecting discernibly different light intensities. Moreover, pits and lands have sharp, well-defined boundaries
22
, so that it is possible to precisely identify the location where a pit ends and a land begins and where a land ends and a pit begins. The boundary
22
between one region and another is known as a “transition”.
Data is recorded on to Digital Optical Media in a spiral track along which these patterns of pits and lands are laid out in a linear fashion. As the media spins, the laser light sweeps along the track and whenever the intensity of the reflected light changes from one value to another, i.e. when the incident light passes either from land to pit or from pit to land, the detector circuitry signals that a transition has occurred. It is not the intensity of the reflected light, but rather the precise timing of these transitions from one intensity to the other (relative to a data clock maintained within the digital data detector of the medium reader) which represents the digital data recorded on the media.
Data Representation
Digital data is represented within a computer or optical media player as a series of “bits” (binary digits, i.e., 1's and 0's), where 8 bits are typically grouped into a data unit referred to as a “byte”. In general, the sequence of bits is unconstrained in the sense that any specific bit can be succeeded by a 1 or a 0. It is not desired, however, to record unconstrained data on digital optical media using the recording technique previously described (i.e., if pits represent 1's and lands represent 0's or if a transition occurs only when a 1is recorded), because transitions may then occur too frequently or not frequently enough, depending on the data. For example, a long sequence of 1's or a long sequence of 0's would result in a very long space between transitions, and this would cause the data decoder clock to lose synchronization with the data recorded on the track. Moreover, on extremely long runs of 1's or 0's would cause a very long space to occur between successive pits in the in-track direction, this could interfere with the ability of the playback spot to follow such a track. A series of alternating 1's and 0's on the other hand would result in a very short space between transitions and would require the disc reader to have an extremely small focused spot size. To avoid these problems, therefore, prior to recording,. every byte of data is instead encoded to convert it to a constrained binary sequence that exhibits at least a desired minimum number of 0's, but not more than a desired maximum number of 0's, between any two 1's.
For example, on a CD, data bytes are converted to a 14-bit constrained sequence using a mapping known as the Eight-to-Fourteen-Modulation (EFM) code, as is partially illustrated by way of example in the table of
FIG. 2
, to which reference is now briefly made. The table of
FIG. 2
comprises two columns, referenced
26
and
28
, which list the byte values and the corresponding channel bit EFM codes, respectively. Each 14-bit EFM code sequence observes strict limits in the spacing of the transitions along the digital optical media data track. In the EFM code sequences, transitions are indicated by 1's and no variation of the media track feature (i.e., pit or land) is indicated by 0's, but only certain patterns are used. Valid EFM code sequences have the property that transitions occur no closer than three (3) length units from one another, and no further than eleven (11) length units from another. The value of a length unit which corresponds to a single EFM code bit, may vary from one embodiment to another, but in CD digital optical media it is nominally on the order of 0.3 micrometers. There are 256 different valid EFM codes which have been arbitrarily assigned to represent the 256 different byte patterns, and it is the EFM code sequences which are actually recorded on the digital optical media data track. The individual bits of these code sequences are referred to as “channel bits” of the recorded data, of which EFM encoding is but one embodiment of channel coding.
Referring briefly to
FIG. 3
which is a schematic illustration of digital signals, the player detects transitions and indicates them by a pulse
30
in time, and it indicates an absence of transition by a constant signal value
32
. This pulse signal can be obtained by taking a rectified derivative of signal
34
which is output by the disc player as its focused read spot scans the data track segment formed by pits
20
(FIG.
1
). When the signal is plotted as an ordinate
38
against a time abscissa divided into suitable time units
36
, which correspond to the scanning of a single lengt

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