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T13/2132-D Revision 3 June 23, 2010
32 Working Draft Enhanced Disk Drive - 4 (EDD-4)
8.4 Read Sectors into Memory (FN 02h)
This function shall be used to read data from the device into the host memory buffer beginning at the location
specified by the contents of the ES:BX registers. If the command transfers some of the data and then returns a
failure, carry is set, the buffer pointed to by ES:BX shall contain the partial data transfer, and AH shall contain an
error code. When there is a partial data transfer, there is no reliable indication of what part of the data was
successfully transferred. Some systems use DMA to return the data in an out-of-order fashion. This function
does not have a mechanism to report what data is valid in the case of a partial transfer. In some conventional
systems when a partial transfer occurs, AL contains the number of sectors transferred.
Entry
AH 02h
AL Number of sectors to read, shall be greater than 0 and less than 128
CH Low order 8 bits of the cylinder number
CL
Bit Description
7:6 high order 2 bits of the cylinder
5:0 sector number
DH Head number
DL BIOS device number
ES:BX Pointer to destination buffer in memory
Exit
Carry Clear Function completed without error
AH Shall be cleared to zero
AL Number of sectors read
ES:BX Pointer to buffer filled with read data
Carry Set Function completed with an error
AH Shall be set to the error code
AL Vendor Specific
ES:BX Pointer to buffer partially filled with read data