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FDC87W22

Power I/O Controller

SMSC -> Microchip 

FDC FUNCTIONAL DESCRIPTION

FDC87W22 FDC

The floppy disk controller of the FDC87W22

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 1 M

bits/sec data rate.

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 500K BPS

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 1M BPS

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

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