45 lines
1.8 KiB
Plaintext
45 lines
1.8 KiB
Plaintext
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####################
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# Read Disk Sector #
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####################
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System programming:
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-------------------
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(Int 13h, ah=2)
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in 1f7 until BSY cleared
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out 1f2, AL # number of sectors
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out 1f3, cl (bits 0-5) # starting sector number
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out 1f4, ch # cylinder number bits 0..7, 0 based
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out 1f5, cl (bits 6,7) & dh (bits 6,7) # cyl, bits 8..9, 10..11
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out 1f6, dh (bits 0..3) --> bits 0..3 # head number
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dh (bits 4..5) --> ??? # head number
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dl (bit 0) --> bit 4 # drive number
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out 1f7, 0x20 # read sectors command normal
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Drive response:
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---------------
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* drive sets the busy bit in Status Reg to 1
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* if command parameters are wrong:
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> drive sets the aborted-command bit in the Error register and
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error bit in the Status register to 1.
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> Drive also sets the busy bit in the Status register to 0.
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> Drive then generates an interrupt to the system.
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* else:
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> drive executes an implied seek to desired track and
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reads sectors into sector buffer
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> when sector buffer is filled and the data is ready to be
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transferred, the drive sets the data-request bit to 1, sets
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the busy bit to 0, and generates an interrupt.
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> on a single-sector transfer, after the system has transferred
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the data, the drive sets the data-request bit and the busy bit to 0.
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> on a multiple-sector transfer, after the system has transferred
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the first sector of data, the drive sets the data-request bit to 0,
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and the busy bit to 1. When each subsequent sector is ready to be
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transferred, the drive sets the data-request bit to 1, the busy bit to 0,
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and generates an interrupt. When the system has tranferred the last sector,
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the drive sets the data-request bit and busy bit to 0.
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