
SMSC DS – LPC47M14X 
Page 41 
Rev. 03/19/2001 
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 17 for explanations of the various symbols used. Table 18 lists the 
required parameters and the results associated with each command that the FDC is capable of performing. 
Table 17  –  Description of Command Symbols 
SYMBOL
C 
D 
D0, D1 
NAME
DESCRIPTION
Cylinder Address The currently selected address; 0 to 255. 
Data Pattern 
The pattern to be written in each sector data field during formatting. 
Drive Select 0-1 
Designates which drives are perpendicular drives on the 
Perpendicular Mode Command.  A "1" indicates a perpendicular 
drive. 
Direction Control 
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. 
Disk Drive Select           DS1          DS0          DRIVE 
            0              0            Drive 0 
            0              1            Drive 1 
Special Sector 
Size 
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.                        
Enable Count 
When this bit is "1" the "DTL" parameter of the Verify command 
becomes SC (number of sectors per track). 
Enable FIFO 
This active low bit when a 0, enables the FIFO.  A "1" disables the 
FIFO (default). 
Enable Implied 
Seek 
read or write command that requires the C parameter in the 
command phase.  A "0" disables the implied seek. 
End of Track 
The final sector number of the current track. 
Alters Gap 2 length when using Perpendicular Mode. 
Gap Length 
The Gap 3 size.  (Gap 3 is the space between sectors excluding the 
VCO synchronization field). 
Head Address 
Selected head:  0 or 1 (disk side 0 or 1) as encoded in the sector ID 
field. 
Head Load Time 
The time interval that FDC waits after loading the head and before 
initializing a read or write operation.  Refer to the Specify command 
for actual delays. 
Head Unload 
Time 
write command) until the head is unloaded.  Refer to the Specify 
command for actual delays. 
Lock defines whether EFIFO, FIFOTHR, and PRETRK parameters of 
the CONFIGURE COMMAND can be reset to their default values by 
a "software Reset". (A reset caused by writing to the appropriate bits 
of either the DSR or DOR) 
MFM/FM Mode 
Selector 
density (FM) mode. 
DIR 
DS0, DS1 
DTL 
By setting N to zero (00), DTL may be used to control the number of 
EC 
EFIFO 
EIS 
When set, a seek operation will be performed before executing any 
EOT 
GAP 
GPL 
H/HDS 
HLT 
HUT 
The time interval from the end of the execution phase (of a read or 
LOCK 
MFM 
A one selects the double density (MFM) mode.  A zero selects single