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FDC87W21

Power I/O Controller with Fast Infrared Support

SMSC -> Microchip 

FDC FUNCTIONAL DESCRIPTION

FDC87W21 FDC

The floppy disk controller of the FDC87W21

integrates all of the logic required for floppy disk

control. The FDC implements a PC/AT or PS/2

solution. All programmable options default to

compatible values. The FIFO provides better

system performance in multi-master systems.

The digital data separator supports up to data

rate 1 Mbps. (2 Mbps for fast tape drive with 48

MHz crystal in.) The FDC includes the following

blocks: AT Interface, Precompensation, Data

Rate Selection, Digital Data Separator, FIFO,

and FDC Core.

AT Interface

The interface consists of the standard

asynchronous signals: nRD, nWR, A0-A3, IRQ,

DMA control, and a data bus. The address lines

select between the configuration registers, the

FIFO and control/status registers. This interface

can be switched between PC/AT, Model 30, or

PS/2 normal modes. The PS/2 register sets are

a superset of the registers found in a PC/AT.

FIFO (Data)

The FIFO is 16 bytes in size and has

programmable threshold values. All command

parameter information and disk data transfers

go through the FIFO. Data transfers are

governed by the RQM and DIO bits in the Main

Status Register. The FIFO defaults to disabled

mode after any form of reset. This maintains

PC/AT hardware compatibility. The default

values can be changed through the

CONFIGURE command. The advantage of the

FIFO is that it allows the system a larger DMA

latency without causing disk errors. The

following tables give several examples of the

delays with a FIFO. The data are based upon

the following formula:

THRESHOLD × (1/Data Rate) *8 - 1.5 µS =

DELAY

FIFO THRESHOLD

1 Byte

2 Byte

8 Byte

15 Byte

FIFO THRESHOLD

1 Byte

2 Byte

8 Byte

15 Byte

MAXIMUM DELAY TO SERVICING AT 500 KBPS

Data Rate

1 × 16 µS - 1.5 µS = 14.5 µS

2 × 16 µS - 1.5 µS = 30.5 µS

8 × 16 µS - 1.5 µS = 6.5 µS

15 × 16 µS - 1.5 µS = 238.5 µS

MAXIMUM DELAY TO SERVICING AT 1 MBPS

Data Rate

1 × 8 µS - 1.5 µS = 6.5 µS

2 × 8 µS - 1.5 µS = 14.5 µS

8 × 8 µS - 1.5 µS = 62.5 µS

15 × 8 µS - 1.5 µS = 118.5 µS

17

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