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FLOPPY DISK INTERFACE

If

the

Write Sector

command

specified a

multiple

sector

transfer,

the

Sector Register is

incremented

and

the

process

repeated,

starting

from

the

verification operation

on

the

next

ID field.

The

multiple

sector

transfer operation

continues

until

terminated

either

by issuing a Force

Interrupt

command,

or after

the

sector

number

is

incremented

to

a

value

exceeding

the

number

of sectors

on

the

track.

In

the

latter

case,

the

FDC

automatically

terminates

the

command

after five revolutions of

the

disk,

since

the

verification of

the

ID field

will

not

be able

to

locate a

matching

sector

number.

Failure of

the

lOP

to

write

the

first data

byte

to

the

Data

Register before

the

arrival of

the

sector

data

field causes

the

FDC to,

set

the

Lost

Data

bit

in

the

Status

Register,

activate

the

INTRQ

output,

and

abort

the

command.

Failure of

the

lOP

to

supply a

data

byte

to

the

Data

Register

on

receiving a

DMA

request

after

the

first

byte

(i.e.

within

16

jLs),

causes

the

FDC

to

write

a

byte

of zeroes

onto

the

disk

and

also

set

the

Lost

Data

bit,

but

does

not

terminate

the

command

sequence.

Read Sector.

On

receipt

of

the

Read Sector

command,

the

FDC begins

the

process of searching

the

sector ID fields of

the

track

for

the

desired

source

of data.

When

an

ID field is

found

with

the

correct

track

number

(as

specified by

the

Track

Register),

the

correct side

number

(as

specified by

the

U

bit

in

the

command),

the

correct sector

number

(as

specified by

the

Sector Register),

and

the

correct

CRC

character;

the

FDC

reads

the

data

bytes from

the

following

data field,

and

informs

the

lOP, via

the

DRQ

output,

every

time

a data

byte

is

stored

in

the

Data

Register.

If

an

ID field is

not

found

containing

the

correct

information

within

five

revolutions

of

the

disk,

the

command

is

aborted

and

the

Record

Not

Found

bit

in

the

Status

Register set.

If

any

of

the

ID fields

encountered,

contain

an

incorrect

CRC

character,

this

is also recorded

in

the

Status

Register.

Failure of

the

lOP

to

read

the

contents

of

the

Data

Register before

it

is

overwritten

with

the

next

byte

of

data

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Other manuals for ACT apricot

Service Manual305 pages