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IT8673F
11.4.10 Command Set
The FDC utilizes a defined set of commands to communicate with the host. Each command is comprised of
a unique first byte, which contains the op-code, and a series of additional bytes, which contain the required
set of parameters and results. The op-code byte indicates to the FDC how many additional bytes should be
expected for the command being written. The descriptions use a common set of parameter byte symbols,
which are presented in Table 11-14. The FDC commands may be executed whenever the FDC is in the
Command phase. The FDC checks to see that the first byte is a valid command and, if so, proceeds. An
interrupt is issued if it is not a valid command.
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Table 11-14. Command Set Symbol Descriptions
Symbol
Name
Description
C
Cylinder Number
The current/selected cylinder (track) number: 0
255.
D
Data
The data pattern to be written into a sector.
DC3
DC0
Drive Configuration
Bit3-0
Designate which drives are perpendicular drives on the PERPENDICULAR
MODE command.
DIR
Direction Control
Read/Write Head Step Direction Control. 0 = Step Out; 1 = Step In.
DR0, DR1
Disk Drive Select
The selected drive number: 0 or 1.
DTL
Data Length
When N is defined as 00h, DTL designates the number of data bytes which users
are going to read out or write into the Sector. When N is not 00h, DTL is
undefined.
DFIFO
Disable FIFO
A “1” will disable the FIFO (default). A “0” will enable the FIFO.
EC
Enable Count
If EC=1, DTL of VERIFY command will be SC.
EIS
Enable Implied Seek
If EIS=1, a SEEK operation will be performed before executing any READ or
WRITE command that requires the C parameter.
EOT
End of Track
The final sector number on a cylinder. During a READ or WRITE operation, the
FDC stops data transfer after the sector number is equal to EOT.
GAP2
Gap 2 Length
By PERPENDICULAR MODE command, this parameter changes Gap 2 length in
the format.
GPL
Gap Length
The length of Gap 3. During a FORMAT command, it determines the size of Gap
3.
H
Head Address
The Head number 0 or 1, as specified in the sector ID field. (H = HD in all
command words.)
HD
Head
The selected Head number 0 or 1. Also controls the polarity of HDSEL#. (H = HD
in all command words.)
HLT
Head Load Time
The Head Load Time in the FDD (2 to 254 ms in 2 ms increments).
HUT
Head Unload Time
The Head Unload Time after a READ or WRITE operation has been executed (16
to 240 ms in 16 ms increments).
LOCK
If LOCK=1, DFIFO, FIFOTHR, and PRETRK parameters of the CONFIGURE
command will not be affected by a software reset. If LOCK=0 (default), the above
parameters will be set to their default values following a software reset.