LPC47M14X datasheet(50/205 Pages) SMSC

50 / 205 page

SMSC DS – LPC47M14X

Page 50

Rev. 03/19/2001

6.5.4

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 is 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 (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 Table 19 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.

Table 19 – Sector Sizes

SECTOR SIZE

128 bytes

256 bytes

512 bytes

1024 bytes

...

16 Kbytes

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 Table 20.

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 "01"

indicating abnormal termination, sets the ND bit in Status Register 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. Table 21 describes the effect of the SK bit on the Read Data command execution and results.

Except where noted in Table 21, the C or R value of the sector address is automatically incremented (see Table 23).

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