ACT apricot - Read;Write Head Positioning

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FLOPPY DISK INTERFACE

Read/Write Head Positioning

Prior

to

performing

any

of

the

disk transfer

routines

described above,

the

read/write

head

has

to be positioned

over

the

required

track

on

the

selected disk and

the

head

load control signal

issued

to

engage

the

read/write head.

The

head positioning

operation

is achieved

under

software

control by issuing a

command

byte

to

the

FDC.

The

FDC responds

to

five different head positioning

command

bytes;

each

moves

the

head

to a position specified

by

the

command.

The

five

commands

are Restore, Seek,

Step, Step-in

and

Step-out.

The

function

of each

command

is detailed

in

the

table below.

Head

Positioning

Commands

Command

Function

Restore Positions

the

head

over

Track

0

on

the

Disk.

Seek Positions

the

head to

the

track

number

specified

in

the

Data

Register.

Step

Moves

the

head

to

an

adjacent

track

in

the

same

direction

as

the

previous

head

posi

tioning

command.

Step-in Moves

the

head

to

the

adjacent

track

in

the

direction

away

from

Track

o.

Step-out Moves

the

head

to

the

adjacent

track

in

the

direction

towards

Track

o.

On

completion

of a

head

positioning

command,

the

FDC

generates

an

interrupt

request

on

the

INTRQ

output

to

indicate

to

the

CPU

the

end

of

the

command

cycle. Reading

the

Status

Register

or

writing

a

new

command

to

the

FDC

resets

the

INTRQ

output.

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Other manuals for ACT apricot

Service Manual305 pages