Browse Prior Art Database

Diskette Scan Mechanism

IP.com Disclosure Number: IPCOM000049103D
Original Publication Date: 1982-May-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Bradley, DJ: AUTHOR [+4]

Abstract

A "key" searching arrangement is disclosed for transferring a predetermined sector of information from the diskette storage device 10 to the buffer area 11 of memory 12. The direct memory access (DMA) controller 14 is set to read from the diskette storage 10 into memory 12, specifically the buffer area 11. DMA 14 is set to transfer one byte more than is in one sector on the diskette. In practice, the sector contains 256 bytes, so the DMA 14 is set to transfer 257 bytes. The diskette controller portion of the microprocessor 16 is set to read all the sectors on one track.

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Diskette Scan Mechanism

A "key" searching arrangement is disclosed for transferring a predetermined sector of information from the diskette storage device 10 to the buffer area 11 of memory 12. The direct memory access (DMA) controller 14 is set to read from the diskette storage 10 into memory 12, specifically the buffer area 11. DMA 14 is set to transfer one byte more than is in one sector on the diskette. In practice, the sector contains 256 bytes, so the DMA 14 is set to transfer 257 bytes. The diskette controller portion of the microprocessor 16 is set to read all the sectors on one track.

After the first 32 bytes have been transferred from the first sector to the buffer, the "key" being searched for is compared against the appropriate byte positions in the buffer. If the key is found, the remainder of the sector is transferred to the buffer and the operation is completed by sensing the Compare Equal and the Interrupt signal generated when the "one more byte" (#257) is detected.

If the results of the compare are not equal, the DMA controller 14 is reset and the next sector is read into the buffer, overriding the first sector, and the process is repeated.

The scan process is terminated when the last sector on the diskette track is detected and the key being searched for has not been found.

This method allows all the sectors on a diskette track to be scanned in a single revolution and, when the desired sector is found, for that sector to be read into the storag...