Result Phase
The generation of FINT determines the
beginning of the result phase. For each of the
commands, a defined set of result bytes has to
be read from the FDC before the result phase is
complete. These bytes of data must be read out
for another command to start.
RQM and DIO must both equal "1" before the
result bytes may be read. After all the result
bytes have been read, the RQM and DIO bits
switch to "1" and "0" respectively, and the CB bit
is cleared, indicating that the FDC is ready to
accept the next command.
COMMAND SET/DESCRIPTIONS
Commands can be written whenever the FDC is
in the command phase. Each command has a
unique set of needed parameters and status
results. The FDC checks to see that the first
byte is a valid command and, if valid, proceeds
with the command. If it is invalid, an interrupt
is issued. The user sends a Sense Interrupt
Status command which returns an invalid
command error. Refer to Table 18 or
explanations of the various symbols used. Table
19 lists the required parameters and the
results associated with each command that the
FDC is capable of performing.
SYMBOL
C
D
D0, D1,
D2, D3
DIR
DS0, DS1
DTL
EC
NAME
Cylinder
Address
Data Pattern
Drive Select 0-
3
Direction
Control
Disk Drive
Select
Special Sector
Size
Enable Count
Table 18 - Description of Command Symbols
DESCRIPTION
The currently selected address; 0 to 255.
The pattern to be written in each sector data field during formatting.
Designates which drives are perpendicular drives on the Perpendicular
Mode Command. A "1" indicates a perpendicular drive.
If this bit is “0”, then the head will step out from the spindle during a
relative seek. If set to a “1”, the head will step in toward the spindle.
DS1 DS0 DRIVE
0 0 drive 0
1 1 drive 1
1 0 drive 2
1 1 drive 3
By setting N to zero (00), DTL may be used to control the number of
bytes transferred in disk read/write commands. The sector size (N =
0) is set to 128. If the actual sector (on the diskette) is larger than
DTL, the remainder of the actual sector is read but is not passed to
the host during read commands; during write commands, the
remainder of the actual sector is written with all zero bytes. The CRC
check code is calculated with the actual sector. When N is not zero,
DTL has no meaning and should be set to FF HEX.
When this bit is "1" the "DTL" parameter of the Verify command
becomes SC (number of sectors per track).
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