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