1 #################### 2 # Read Disk Sector # 3 #################### 4 5 System programming: 6 ------------------- 7 8 (Int 13h, ah=2) 9 in 1f7 until BSY cleared 10 out 1f2, AL # number of sectors 11 out 1f3, cl (bits 0-5) # starting sector number 12 out 1f4, ch # cylinder number bits 0..7, 0 based 13 out 1f5, cl (bits 6,7) & dh (bits 6,7) # cyl, bits 8..9, 10..11 14 out 1f6, dh (bits 0..3) --> bits 0..3 # head number 15 dh (bits 4..5) --> ??? # head number 16 dl (bit 0) --> bit 4 # drive number 17 out 1f7, 0x20 # read sectors command normal 18 19 20 21 Drive response: 22 --------------- 23 24 * drive sets the busy bit in Status Reg to 1 25 * if command parameters are wrong: 26 > drive sets the aborted-command bit in the Error register and 27 error bit in the Status register to 1. 28 > Drive also sets the busy bit in the Status register to 0. 29 > Drive then generates an interrupt to the system. 30 * else: 31 > drive executes an implied seek to desired track and 32 reads sectors into sector buffer 33 > when sector buffer is filled and the data is ready to be 34 transferred, the drive sets the data-request bit to 1, sets 35 the busy bit to 0, and generates an interrupt. 36 > on a single-sector transfer, after the system has transferred 37 the data, the drive sets the data-request bit and the busy bit to 0. 38 > on a multiple-sector transfer, after the system has transferred 39 the first sector of data, the drive sets the data-request bit to 0, 40 and the busy bit to 1. When each subsequent sector is ready to be 41 transferred, the drive sets the data-request bit to 1, the busy bit to 0, 42 and generates an interrupt. When the system has tranferred the last sector, 43 the drive sets the data-request bit and busy bit to 0. 44 45
