Write protection and data detection using differential detector

Details Write protection and data detection using differential detector Write protection and data detection using differential detector

1984-02-08

1986-08-12

Canney, Vincent P.

Dynamic information storage or retrieval

Condition indicating, monitoring, or testing

Including radiation storage or retrieval

369 58, G11B 390, G11B 2736

Patent

active

046060162

ABSTRACT:
Disclosed is an apparatus for detection of write protect data written on an optical disk by simultaneously reading the data during writing using differential detection and disabling further writing if write protect data is present. The write protect data is the same format as other data written on the optical disk and is written as the first byte of data on all data fields. The data is written in a fixed-block format defining a symbol having a predetermined number of symbol positions and a predetermined number of holes which may be written at the symbol positions, an equal number of holes at odd and at even positions. The write protect symbol has holes written at symbol position numbers two and five. During the writing of a write protect symbol, the laser is operated at read power before it is operated at write power and a signal associated with the hole associated power of the reflected beam is sampled at position number eight of the previous symbol and at position number one of the write protect symbol. The hole associated power at position number one will be significant if a hole was previously written at position number two. The read signals at positions one and eight are compared to each other. If the position number one signal exceeds that at number eight by a predetermined differential, a hole was previously recorded at position number two, indicating the presence of a previously written write protect byte of data.
The same apparatus is also used to detect the presence of or absence of data in a data sector during read mode.

REFERENCES:
patent: 4546462 (1985-10-01), Koishi et al.

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