Commodore Amiga A500 Technical Reference Manual page 187

Initialize Unit 1
(Opcode CC)
Change Command
Block
(Class 0, Opcode F)
This four bit field can be used to specify options as indicated below:
Bit 7 = 0
= 1
Bit 6 = 0
= 1
Bit 5 = 0
Bit 4 = 0
Step Rate
Step Rate 14 = 11.1 usec
Step Rate 15 = 30 usec
All Others =
Possible Error Codes
No error, invalid command, DMA error.
Action
This command with initialize or set drive parameters of unit 1 only.
This allows for the HDC to support two different drive types at the
same time. The action of this command is identical to the action of
the 'Set Drive Parameter' command noted above except that it will
effect only unit 1. For command details see section 6.2.9.
Action
The Change Command Block is used to move the location of the
command block from the default on power up to a new location.
Bytes 6 and 7 of the command block are used as indirect address
pointers for the beginning of a 7 byte block of memory organized as
follows:
Table 5-10. Change Command Block Address
D7 D6 D5
0
A23
A15
A07
184
5 bit correction span (default value)
11 bit correction span
Retries & ECC enabled (default value)
Retries & ECC disabled
Not Used
Not Used
3 msec
D4 D3 D2
High Order DMA Byte
Mid Order DMA Byte
Low Order DMA Byte
D1 D0
0
A16
A08
0