PC8477B datasheet(4/54 Pages) NSC

4 / 54 page

10 Introduction

The PC8477B advanced floppy disk controller is suitable for

all PC-AT EISA PS2 and general purpose applications

The operational mode (PC-AT PS2 and Model 30) of the

PC8477B is determined by hardware strapping of the IDENT

and MFM pins DP8473 and Intel 82077AA software com-

patibility is provided Key features include the 16 byte FIFO

PS2 diagnostic register support the perpendicular record-

ing mode CMOS disk interface and a high performance

analog data separator

The PC8477B supports the standard PC data rates of 250

300 500 kbs and 1 Mbs in MFM encoded data mode but

is no longer guaranteed through functional testing to sup-

port the older FM encoded data mode References to the

older FM mode remain in this document to clarify the true

functional operation of the device

The 1 Mbs data rate is used by new high performance tape

and floppy drives emerging in the PC market today The new

floppy drives utilize high density media which requires the

PC8477B supported perpendicular recording mode format

When used with the 1 Mbs data rate this new format allows

the use of 4 Mb floppy drives which format ED media to

288 MB data capacity

The high performance internal analog data separator needs

no external components It improves on the window margin

performance standards of the DP8473 and is compatible

with the strict data separator requirements of floppy and

floppy-tape drives

The PC8477B contains write precompensation and circuitry

that will default to 125 ns for 250 300 and 500 kbs

4167 ns at 1 Mbs These values can be overridden

through software to disable write precompensation or to

provide levels of precompensation up to 250 ns The

PC8477B has internal 12 mA data bus buffers which allow

direct connection to the system bus The internal 48 mA

totem-pole disk interface buffers are compatible with both

CMOS drive inputs and 150X resistor terminated disk drive

inputs

The PC8477B is available in a 68 pin Plastic Leaded Chip

Carrier (PLCC) package and in a 60 pin Plastic Quad Flat

Package (PQFP)

PC8477B Datasheet(PDF) 4 Page - National Semiconductor (TI)