MPI 40 Series - General Control Timi~G; Data Encoding and Recovery; Data Encoding

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3.6.8 General Control Timing

Timing

requirements

for

the

necessary

sequence

of

events

for

control

and

data

are

shown

in

Figure

3-5.

These

timing

restrictions

are

necessary

for

proper

operation.

3.7

DATA

ENCODING AND RECOVERY

This

section

provides

applications

information

relevant

to

the

record-

ing

and

recovery

of

data

with

the

Model 40

Series

Disk

Drives.

The most

common

methods

for

encoding

data

are

described

in

the

following

paragraphs.

3.7.1 Data Encoding

BIT

CELLS

FM

The Model 40

Series

can

be

used

as

either

single

density

or

double

density

units.

For

single

density,

the

FM

encoding

scheme

is

adequate

while

in

double

density

drives,

MFM

encoding

scheme

is

recommended.

Due

to

the

higher

efficiency

of

MFM

encoding,

the

bit

cell

period

is

one

half

of

FM

code

and

thus

double

density

recording

can

be

achieved.

See

Figure

3-13

for

a

comparison

of

FM

and

MFM

encoding

schemes.

1

1

1

0

1 0 0

0

1

I 2F

:__

-t

I

I

-i

I

1F

i-

BIT

CELLS

MFM

1

1 1

0 1 0 0 0

1

D

o

____

o,___

....

-!

1

2F

1

-

1

-J

I I

1-1F--l

I I

4/3F

I--

:-

4/5F

I

Figure 3-13:

FM

and MFM Code Comparisons

3-23

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