SCH3112I-NE SMSC [SMSC Corporation], SCH3112I-NE Datasheet - Page 81

• Manufacturer Part Number: SCH3112I-NE
• Description: LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
• Manufacturer: SMSC [SMSC Corporation]

LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
Datasheet
SMSC SCH311X
READ DATA
A set of nine (9) 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 the TC cycle, 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
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.
The amount of data which can be handled with a single command to the FDC depends upon MT (multi-
track) and N (number of bytes/sector).
The Multi-Track function (MT) allows the FDC to read data from both sides of the diskette. For a
particular cylinder, data will be transferred starting at Sector 1, Side 0 and completing the last sector
of the same track at Side 1.
If the host terminates a read or write operation in the FDC, the ID information in the result phase is
dependent upon the state of the MT bit and EOT byte. Refer to
At the completion of the Read Data command, the head is not unloaded until after the Head Unload
Time Interval (specified in the Specify command) has elapsed. If the host issues another command
before the head unloads, then the head settling time may be saved between subsequent reads.
If the FDC detects a pulse on the nINDEX pin twice without finding the specified sector (meaning that
the diskette’s index hole passes through index detect logic in the drive twice), the FDC sets the IC
code in Status Register 0 to
1 to “1” indicating a sector not found, and terminates the Read Data Command.
After reading the ID and Data Fields in each sector, the FDC checks the CRC bytes. If a CRC error
occurs in the ID or data field, the FDC sets the IC code in Status Register 0 to “01” indicating abnormal
termination, sets the DE bit flag in Status Register 1 to “1”, sets the DD bit in Status Register 2 to “1”
if CRC is incorrect in the ID field, and terminates the Read Data Command.
effect of the SK bit on the Read Data command execution and results. Except where noted in
Table
page
67).
7.18, the C or R value of the sector address is automatically incremented (see
N
00
01
02
03
..
07
Table 7.16 Sector Sizes
“01” indicating abnormal termination, sets the ND bit in Status Register
DATASHEET
SECTOR SIZE
128 bytes
256 bytes
512 bytes
1024 bytes
…
16 Kbytes
65
Table
7.16). If N is set to zero, the sector size is
Table
7.17.
Table 7.18
Rev 0.2 (09-28-04)
Table 7.20 on
describes the