FDC37M607 datasheet(25/182 Pages) SMSC

25 / 182 page

DATA REGISTER (FIFO)

Address 3F5 READ/WRITE

All command parameter information, disk data

and result status are transferred between the

host processor and the floppy disk controller

through the Data Register.

Data transfers are governed by the RQM and

DIO bits in the Main Status Register.

The Data Register defaults to FIFO disabled

mode after any form of reset.

This maintains

PC/AT hardware compatibility.

The default

values can be changed through the Configure

command (enable full FIFO operation with

threshold control). The advantage of the FIFO

is that it allows the system

a larger DMA

latency without causing a disk error. Table 14

gives several examples of the delays with a

FIFO.

The data is based upon the following

formula:

At the start of a command, the FIFO action is

always disabled and command parameters

must be sent based upon the RQM and DIO bit

settings. As the command execution phase is

entered, the FIFO is cleared of any data to

ensure that invalid data is not transferred.

An overrun or underrun will terminate the

current command and the transfer of data. Disk

writes will complete the current sector by

generating a 00 pattern and valid CRC. Reads

require the host to remove the remaining data

so that the result phase may be entered.

Table 14 - FIFO Service Delay

FIFO THRESHOLD

EXAMPLES

MAXIMUM DELAY TO SERVICING AT 2

Mbps* DATA RATE

1 byte

2 bytes

8 bytes

15 bytes

1 x 4

µs - 1.5 µs = 2.5 µs

2 x 4

µs - 1.5 µs = 6.5 µs

8 x 4

µs - 1.5 µs = 30.5 µs

15 x 4

µs - 1.5 µs = 58.5 µs

FIFO THRESHOLD

EXAMPLES

MAXIMUM DELAY TO SERVICING AT 1

Mbps DATA RATE

1 byte

2 bytes

8 bytes

15 bytes

1 x 8

µs - 1.5 µs = 6.5 µs

2 x 8

µs - 1.5 µs = 14.5 µs

8 x 8

µs - 1.5 µs = 62.5 µs

15 x 8

µs - 1.5 µs = 118.5 µs

FIFO THRESHOLD

EXAMPLES

MAXIMUM DELAY TO SERVICING AT

500 Kbps DATA RATE

1 byte

2 bytes

8 bytes

15 bytes

1 x 16

µs - 1.5 µs = 14.5 µs

2 x 16

µs - 1.5 µs = 30.5 µs

8 x 16

µs - 1.5 µs = 126.5 µs

15 x 16

µs - 1.5 µs = 238.5 µs

*The 2 Mbps data rate is only available if VCC = 5V.

Threshold # x

DATA RATE

x 8

- 1.5

µs = DELAY

FDC37M607 Datasheet(PDF) 25 Page - SMSC Corporation

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