Commodore Amiga A500 Technical Reference Manual page 191

Read Long
(Class 7, Opcode
5)
Write Long
(Class 7, Opcode
6)
Since the host
R/W
bit, and address bits A23-A17, form the data
byte for the host LD2- counter, the
DMA
high and middle order ad-
dress bytes are shifted right
1
bit position before being used. Since a
copy of the previous address is not maintained, the command status
is returned to the new address location specified and not the old one.
Possible Error Codes
No error, invalid command,
DMA
error.
Action
Similar to Read Sector except the ECC operation producing the
syndrome is inhibited in the HDC. Instead the HDC copies the
recorded CHECK bytes from the disk and passes them unaltered to
the host. This command is useful in debugging and verifying the ECC
hardware and software. To do this first write normally, and then
READLONG. The data or the check bits may now be altered by the
host and written to the disk using the WRITELONG command.
If
a
READ command were issued, then the HDC should invoke error cor-
rection on the data field and correct it as long as the error
induced is within the correction capability of the ECC polynomial.
Because there is no storage register on board, this command is im-
plemented only for diagnostic purposes. Also note that the
4
extra
checkbytes are to be accessed directly to the host. Hence the diag-
nostic tester used is required to support a
S1
6 byte block transfer
instead of the standard 51 2 byte block transfer supported by the
Amiga system.
Possible Error Codes
N o error, invalid command, invalid sector address, invalid
LUN, IDNF
error, bad block mark, address mark not found, write fault, drive not
ready, seek not complete, DMA error.
Action
The Write Long command functions similarly to the Write Sector
command except the ECC operation of computing the ECC word is
inhibited in the HDC. Instead. the HDC accepts a 32 bit appendage
from the host and passes it unaltered to the DJC to be written on the
disk after the data. This command is useful for diagnostic purposes
only. It allows the generation of a sector containing a correctable
ECC error. See the Read Long command description for operation
details and system requirements.