LOCK
DATA BUS
D4 D3 D2 D1 D0
PHASE
Command
Result
R/W
W
R
REMARKS
Command Codes
D7
LOCK
0
D6 D5
0
0
0
0
1
0
0
1
0
0
0
0
0
LOCK
SC is returned if the last command that was issued was the Format command. EOT is returned if the last command
was a Read or Write.
Note: These bits are used internally only. They are not reflected in the Drive Select pins. It is the user’s
responsibility to maintain correspondence between these bits and the Drive Select pins (DOR).
Data Transfer Commands
All of the Read Data, Write Data and Verify type commands use the same parameter bytes and return the same
results information, the only difference being the coding of bits 0-4 in the first byte.
An implied seek will be executed if the feature was enabled by the Configure command. This seek is completely
transparent to the user. The Drive Busy bit for the drive will go active in the Main Status Register during the seek
portion of the command. If the seek portion fails, it will be reflected in the results status normally returned for a
Read/Write Data command. Status Register 0 (ST0) would contain the error code and C would contain the cylinder
on which the seek failed.
Read Data
A set of nine bytes is required to place the FDC in the Read Data Mode. After the Read Data command has been
issued, the FDC loads the head (if it is in the unloaded state), waits the specified head settling time (defined in the
Specify command), and begins reading ID
Address Marks and ID fields. When the sector address read off the diskette matches with the sector address
specified in the command, the FDC reads the sector’s data field and transfers the data to the FIFO.
After completion of the read operation from the current sector, the sector address is incremented by one and the data
from the next logical sector is read and output via the FIFO. This continuous read function is called “Multi-Sector
Read Operation”. Upon receipt of TC, or an implied TC (FIFO overrun/underrun), the FDC stops sending data but will
continue to read data from the current sector, check the CRC bytes, and at the end of the sector, terminate the Read
Data Command. N determines the number of bytes per sector (see Table 37 below). If N is set to zero, the sector
size is set to 128. The DTL value determines the number of bytes to be transferred. If DTL is less than 128, the FDC
transfers the specified number of bytes to the host. For reads, it continues to read the entire 128-byte sector and
checks for CRC errors. For writes, it completes the 128-byte sector by filling in zeros. If N is not set to 00 Hex, DTL
should be set to FF Hex and has no impact on the number of bytes transferred.
SMSC DS – FDC37N769
Page 46 of 137
Rev. 12/21/2000
SMSC [ SMSC CORPORATION ]
