MPI 40 Series - Step in; Spindle Speed Control; Side Selection

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3.6.3.2 Step In

A

true

level

(OV

to

.4V) on

the

DIRECTION

SELECT

line

along

with

pulse(s)

on

the

STEP

line

will

move

the

read/write

heads

towards

the

center

of

the

disk.

3.6.4 Spindle Speed Control

The

spindle

servo

electronics

are

mounted on a

separate

circuit

board

located

at

the

right

rear

of

the

Drive

above

the

diskette

plane.

When

the

MOTOR

ON

signal

becomes

active

{logical

zero),

transistor

Ql {page 1

area

B7)

is

turned

off

and

Q2

is

turned

on,

gating

+24V

to

one

side

of

the

spindle

motor

coils.

Transistors

Q3, Q4, Q5, and

Q6

when

turned

on

simply

provide

a

ground

path

for

the

+24V

on

the

other

side

of

the

coils.

Only one

of

these

transistors

is

turned

on

at

a

time.

They

are

enabled

by

the

signals

HEl,

HEl,

HE2,

and

HE2

which

control

the

base

of

the

transistors

through

the

diodes

in

parallel.

When

both

diodes

in

parallel

are

reversed

biased,

the

transistor

sends

a

ground

to

one

side

of

the

coil

and

the

motor moves

to

that

phase.

When

the

enabled

phase

is

reached,

it

will

be

disabled

and

the

next

phase

enabled;

this

causes

the

motor

to

rotate.

The

four

control

signals

keep

changing

states

by

the

"Hall

Effect"

sensors

mounted

internal

to

the

motor.

The

four

comparators

of

U2

compare

the

sensor

outputs

and

develop

the

control

signals.

As

the

motor

rotates,

HEI

is

used

to

generate

a

pulse

train

at

Ul-1

which,

in

turn,

creates

a

voltage

level

at

the

charge

pump.

This

voltage

is

compared

with

a

reference

voltage

at

pin

10 and

if

it

is

less

than

the

reference

voltage,

the

motor

current

will

be

in-

creased

by

allowing

Ul-8

to

go more

positive

to

the

base

of

Q2

so

that

the

spindle

speed

will

be

increased.

If

the

motor

is

running

too

fast,

then

the

charge

pump

voltage

will

exceed

the

reference

voltage

(Ul-10)

and

the

motor

current

(Ul-8)

will

be

cut

off

which

in

turn

will

reduce

the

spindle

speed.

The

spindle

speed

control

servo

maintains

the

rotating

speed

of

the

motor

within

1-1/2%

of

its

nominal

speed.

3.6.5 Side Selection

In

a

standard

two

sided

drive,

head

selection

is

controlled

by

the

SIDE

SELECT

interface

line

(

Pl-14;

page

3,

area

CB)

• A

false

or

high

level

(2.SV

to

5.25V)

on

the

SIDE

SELECT

line

will

select

the

read/

write

head

on

the

lower

side

(side

0)

of

the

disk

and a

true

or

low

level

{OV

to

.4V) on

the

SIDE

SELECT

line

will

select

the

read/

write

head

on

the

upper

side

(side

1)

of

the

disk.

SIDE

SELECT

is

inverted

by U27-8 {page

3,

area

C7)

and

routed

to

page

2,

area

C8

as

+

Side

Select.

When

selecting

head

~,

the

+

Side

Select

signal

would be a low

level.

Through

inverter

U20-8,

it

is

ANDed

with

+

Erase

to

turn

on

the

erase

circuit

for

head

~.

The

high

level

at

U20-8

(area

B8)

is

sent

through

open-collector

Ul-10

3-20

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