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PC8477BVF-1 Datasheet(PDF) 35 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part # PC8477BVF-1
Description  Advanced Floppy Disk Controller
Download  54 Pages
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Manufacturer  NSC [National Semiconductor (TI)]
Direct Link  http://www.national.com
Logo NSC - National Semiconductor (TI)

PC8477BVF-1 Datasheet(HTML) 35 Page - National Semiconductor (TI)

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50 Functional Description (Continued)
500 kbs
TLF11332 – 11
1 Mbs
TLF11332 – 12
FIGURE 5-4 PC8477B Dynamic Window Margin Performance with g3% ISV at 1 kHz
(Typical performance at VCC e 50V 25 C)
The PC8477B is clocked by a single 24 MHz signal for the
250 kbs 300 kbs 500 kbs and 1 Mbs data rates An
on-chip oscillator is provided to enable the attachment of a
crystal or a clock signal If a crystal is used the following
parameters are required
Crystal Specifications
24 MHz
Parallel Resonant (preferred)
Fundamental Mode
Effective Series
Resistance (ESR)
Less than 50X
Shunt Capacitance
Less than 7 pF
Recommended Crystals
NEL Frequency Controls
24 MHz
24 MHz
24 MHz
A parallel resonant crystal is preferred if at all possible In
some cases a series resonant crystal can be used but care
must be taken to ensure that the crystal does not oscillate
at a sub-harmonic frequency The oscillator circuit is able to
utilize high profile low profile and surface mount type crys-
tal enclosures External bypass capacitors (5 pF to 15 pF)
should be connected from XTAL1 and XTAL2 to GND If an
external oscillator circuit is used it must have a duty cycle of
at least 40% – 60% and minimum input levels of 20V and
08V The controller should be configured so that the exter-
nal oscillator clock is input into the XTAL1CLK pin and
XTAL2 is left unconnected
The performance of the data separator is measured by its
ability to read and decode incoming pulses shifted away
from the nominal position The percentage window margin
indicates how much bit shift the data separator will tolerate
and still be able to read correctly For a Dynamic Window
Margin test all the bits in the data pattern are subject to jitter
(as they would be in a real floppy drive) and the frequency
of the data stream is subject to changes arising from motor
speed variations
Typical dynamic margin performance
curves for the PC8477B are listed in
Figure 5-3 Thse mea-
surements are taken using a FlexStar FS-540 Disk Simula-
tor with a repetitive ‘‘DB6’’ data pattern The graphs indicate
motor speed variation (MSV) vs bit jitter tolerance for the
floppy controller For reliable performance with tape drives
the data separator needs to be able to track to instanta-
neous changes as well
Figure 5-4 shows jitter tolerance vs
MSV with an added instantaneous speed variation (ISV) of
3% at frequency of 1 kHz These are typical performance
curves and measured at VCC e 50V and 25 C A good
data separator should be able to tolerate at least g6%
MSV and 60% window margin
The PC8477B is fully compatible with perpendicular record-
ing mode disk drives at all data rates These perpendicular
mode drives are also called 4 Mbyte (unformatted) or
288 Mbyte (formatted) drives which refers to their maxi-
mum storage capacity Perpendicular recording will orient
the magnetic flux changes (which represent bits) vertically
on the disk surface allowing for a higher recording density
than the conventional longitudinal recording methods With
this increase in recording density comes an increase in the
data rate of up to 1 Mbs thus doubling the storage capaci-
ty In addition the perpendicular 288M drive is readwrite
compatible with 144M and 720k diskettes (500 kbs and
250 kbs respectively)
The 288M drive has unique format and write data timing
requirements due to its readwrite head and pre-erase head
design (see
Figure 5-5 ) Unlike conventional disk drives
which have only a readwrite head the 288M drive has
both a pre-erase head and readwrite head With conven-
tional disk drives the readwrite head by itself is able to
rewrite the disk without problems For 288M drives a pre-
erase head is needed to erase the magnetic flux on the disk
surface before the readwrite can write to the disk surface
The pre-erase head is activated during disk write operations
only ie Format and Write Data commands

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