pc8477b National Semiconductor Corporation, pc8477b Datasheet - Page 4

• Manufacturer Part Number: pc8477b
• Description: Advanced Floppy Disk Controller
• Manufacturer: National Semiconductor Corporation

1 0 Introduction
The PC8477B advanced floppy disk controller is suitable for
all PC-AT EISA PS 2 and general purpose applications
The operational mode (PC-AT PS 2 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
PS 2 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 kb s and 1 Mb s 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 Mb s 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 Mb s data rate this new format allows
the use of 4 Mb floppy drives which format ED media to
2 88 MB data capacity
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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 kb s
41 67 ns at 1 Mb s 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)