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Logic States for the Design of a Hardware Disk Attachment

IP.com Disclosure Number: IPCOM000045007D
Original Publication Date: 1983-Jan-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 3 page(s) / 61K

Publishing Venue

IBM

Related People

Tutt, WE: AUTHOR

Abstract

In designing an attachment for a direct-access storage device (DASD), such as a disk, it is necessary to define logic states for the attachment The attachment must permit the following complement of operations to be initiated by the I/O processor: 1. IDLE 2. READ ID 3. READ RECOVERY 4. WRITE ID 5. READ SECTOR 6. WRITE SECTOR 7. SCAN SECTOR 8. READ ID-VERIFY DATA.

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Logic States for the Design of a Hardware Disk Attachment

In designing an attachment for a direct-access storage device (DASD), such as a disk, it is necessary to define logic states for the attachment The attachment must permit the following complement of operations to be initiated by the I/O processor: 1. IDLE

2. READ ID

3. READ RECOVERY

4. WRITE ID

5. READ SECTOR

6. WRITE SECTOR

7. SCAN SECTOR

8. READ ID-VERIFY DATA.

Fifteen logic states are defined to perform these operations, called states 0 through 14. Some states are modified in length depending on the desired function for the particular sector. The attachment always runs from state B through state 14 for each sector of the DASD. States B-5 concern themselves with the identification (ID) portion of a sector and states 7-14 with the data portion, while state 6 is the transition state. The 15 states are: State 0. - Start of New Sector - Sector Pulse Active.

State 1. - For Read and Compare - First Byte of variable frequency oscillator (VFO)

Sync Field read from disk.

For Write - Write first 15 bytes of VFO Sync Field.

State 2. - For Read and Compare - Second Byte of VFO Sync Field read from disk.

For Write - Write sixteenth byte of VFO Sync Field.

State 3. - For Read and Compare - Remainder of VFO Sync Field. Read from Disk. Wait for

sync detected.

For Write - Write last 2 bytes of VFO Sync Field.

State 4. - For Read - Read 4 bytes of ID field from disk into storage.

For Compare - Compare 4 bytes of ID field on disk

with ID mask in storage.

For Write - Write 4 bytes of ID onto disk

from storage.

State 5. - For Read and Compare - Compare Cycle Redundancy Character (CRC) read from disk

with CRC generated for ID

field.

For Write - Write 2 bytes of CRC from generator onto

disk.

State 6. - For Read and Compare - One byte long transition state

between ID portion and data

portion of sector.

1

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For Write - Three byte long transition state between

ID and data portions of the sector.

State 7. - Same as state 1 except for data portion of sector. State 8. - Same as state 2 except for data portion of sector. State 9. - Same as state 3 except for data portion of sector. State 10. - For Read - Read 256 bytes of data from disk into storage.

For Compare - Compare 256 bytes of data from disk

with 256 bytes of data from storage.

For Write - Write 256 bytes of data from storage to

disk.

State 11. - For Read and Compare - Read first 4 bytes of external check character

(ECC) from disk into ECC

generator.

For Write - W...