Commodore Amiga A500 Technical Reference Manual page 186

Set Drive Parameters
(Class 0, Opcode C)
No error, invalid command, invalid sector address, invalid LUN, drive
not ready, write fault, DMA error.
Action
This command points to a 6 byte block of memory, specified by
bytes 6 and 7 of the command block, that sets the following
parameters for both of the hard disk drives (logical units 0 and 1):
Table 5-9. Set Drive Parameters
D7 D6 D5
User Options
0 Num. Of Heads
Precompensation Cylinder / 16
Reduce Write Current Cylinder / 16
Number of Sector per Track
If the above command is not executed after power up or every
reset, the HDC will assume the following default parameters:
306. = Number of cylinders (131 hex)
4 = Numberof heads
128. = Starting write precompensation cylinder
128. = Reduce write current cylinder
3 mS = Step rate
5 = Maximum length of an error bust to be corrected
17. = Number of sectors per track
8. = Retries & ECC enable
The acceptable range of values for these parameters are as follows:
0 – 2047. Number of cylinders
0 – 7 Number of heads
0 – 255 Sector Numbers
0 – 1023. Starting write precompensation cylinder
5/11. Maximum length of error burst to be corrected
0 / 8 Retries
If one of the parameters is out of range, then an "invalid command"
error code is generated by the HDC. Bytes 2 and 5 of table are self
explanatory and will not be discussed any further.
User Options
183
D4 D3
CYL. Nums. MSN
Number of Cylinders LSB
D2 D1 D0
Step Rate