Commodore 1541-II User Manual

COMMODORE

0

DISK

DRIVE

useris

guide

COMIVIODORE

1541-H

DISK

DRIVE

USER'S

GUIDE

ft

commodore

COMPUTERS

The

information

in

this

manual

has

been

reviewed

andisbelieved

tobeentirely

reliable.

No

responsibility,

however,isassumed

for

inaccuracies.

The

material

in

this

manual

is

for

information

purposes

only,

and

may

be changed

without

notice.

©

Commodore

Electronics

Ltd.,

1986

"All

rights

reserved."

TABLE

OF

CONTENTS

Introduction

1

The

advantages

ofadisk

drive

1

Featuresofthe

1541

1

Howtouse

this

book

2

Basic

Operating

Steps

2

Specifications

of

the

1541

Disk

Drive

4

PART

ONE:

GUIDETOOPERATION

Chapter1:Disk

Drive

5

Unpacking

.

5

Empty

the

drive

6

Connecting

the

cables

6

Turningonthe

power

7

Troubleshooting

guide

9

Simple

maintenance

tips

11

Chapter2:Diskettes

.

12

Whatisa

diskette?

12

Safety

rules

for

diskette

care

13

Inserting

a

diskette

13

Safety

rules

for

removing

diskettes

14

Loadingapackaged

program

14

Howtoprepareanew

diskette

15

Reusinganold

diskette

16

Organizing

a

diskette

library

17

Backups

17

Chapter3:Directories

18

Whatisa

directory?

....

18

Viewingadirectory

18

Whatadirectory

shows

18

Watch

out

for

splat

files

20

Printingadirectory

21

Readingadirectory

asafile

21

Another

waytobe

selective

21

Pattern

matching

and

wild

cards

22

PART

TWO:

GUIDETOADVANCED

OPERATION

AND

PROGRAMMING

Chapter4:Commands

,

25

Command

Channel

25

Reading

the

Error

Channel

26

Housekeeping

hints.

«

28

Saving

programs

29

Save

with

replace

a

30

Verifying

programs

30

Erasing

programs

.

31

Scratch

for

advanced

users

33

Renaming

programs

34

Renaming

and

scratching

troublesome

programs

36

Copying

programs

37

Validating

the

diskette

38

Initializing

40

Chapter

5:

Sequential

Data

Files

42

The

conceptoffiles

42

Openingasequential

file

42

Addingtoa

sequential

file

45

Writing

file

data:

Print#

46

Closingafile

48

Reading

file

data

using

INPUT#

49

More

about

INPUT

(advanced)

50

Numeric

Data

StorageonDiskette

51

Reading

File

Data:

Using

GET#

,...

52

Demonstration

of

Sequential

Files

54

Chapter6:Relative

Data

Files

55

The

valueofrelative

access

55

Files,

Records,

and

Fields

55

File

limits

56

Creating

a

relative

file

56

Using

relative

files:

Record#

57

Completing

relative

file

creation

59

Expandingarelative

file

60

Writing

relative

file

data

61

Designing

a

relative

record

61

Writing

the

record

62

Readingarelative

record

63

The

valueofindex

files

64

Chapter7:Direct

Access

Commands

65

A

tool

for

advanced

users

...

65

Diskette

organization

65

Openingadata channel 65

Block-Read

66

Block-Write

67

The

original

commands

68

The

buffer

pointer

.

69

Allocating

blocks

70

Freeing

blocks 71

Using

random

files

(advanced)

72

Chapter

8:

Internal

Disk

Commands

73

1541

Memory

Map

73

Memory

Read

..

74

Memory

Write

75

Memory

Execute

77

Block

Execute

77

User

commands

78

Chapter

9:

Machine

Language Programs

80

Disk-related

kernafl

subroutines

80

Appendices

A.

Changing

the

Device

Number

81

B.

Error

Messages

83

C.

Diskette

Formats

87

D.

Disk

Command

Quick

Reference

Chart

92

E.

Test/Demo

Diskette

'.

93

ListofFigures

1.

Front

Panel

5

2.

Back

Panel

6

3.

Floppy

Disk

Hookup

8

4.

Position for

Diskette

Insertion

12

INTRODUCTION

The

1541

disk

drive

greatly

increases

the

speed,

storage

capacity,

flexibility

and

reliabil

ityofyour

Commodore

computer.Asyou

use

the

1541

disk

drive,

you

will

appreciate

its

superiority

to

the

cassette

recorder

you

may

have

used

before

andtodisk

drives

offered

for

other

brandsofcomputers.

The

1541-n

disk

driveisfully

compatible

with

the

commodore

1541

disk

drive,

therefore

we

may

often

omit

the

"-II"

suffix

throughout

the

remainder

of

this

manual.

THE

ADVANTAGESOFA

DISK

DRIVE

•

Speed

If

you

have

usedacassette

recorder

for

data

storage,

you

probably

knowitcan

take

up

toanhour

justtosearch

one

long

cassette

tape

looking

foraspecific

program.

With

the

1541

disk

drive,alistofall

the

programsona

diskette

appearsonyour

screen

in

seconds.

The

speedofprogram

loadingisalso

greatly

improved.

It

takes

the

1541

only

a

minutetoloadalarge

program

that

would

takeahalf-hour

to

load

from

tape.

•

Reliability

is

another

reason

for

choosingadisk

drive.Itis

all

too

common

foracassette

usertoaccidentally

eraseavaluable

programbysavinganew

programontopofthe

old

one,

without

realizing

it.

The

1541

disk

drive

automatically

verifies

everything

it

records.

•

Direct

File

Access

A

third

advantageofa

disk

driveisthe

abilitytouse

relative

files

(discussed

in

Chapter

6).Ona

diskette,

any

partofa

relative

file

canbeaccessed

and

altered

separately,

without

affecting

the

restofthe

file.

Overall,

usingadisk

drive

makes

for

easier

and

more

powerful

computing.

FEATURESOFTHE

1541

The

1541isoneofthe

most

affordable

disk

drivesonthe

market.

Compared

to

competitors,

the

1541

has high

capacity,

and

even

higher

intelligence.

Itisoneofthe

most

cost-effective

disk drives

available.

Most

home

and

personal

computers

that

useadisk

takeatleast

10KofRAM

memory

from

the

computertoholdadisk

operating

system

(knownasa

DOS.)

This

large

program

mustbein

memory

the

whole

time

the

disk

is

being

used,

and

muchofit

must

alsobekeptonevery

diskette.

The

Commodore

1541

works

differently

and

more

effectively.

It

contains

its

own

built-in

microcomputer

to

control

its

various

operations,

along

with

enough

ROM

and

RAM

memory

to

operate

without

any

help

from

the

computer.

Commodore's

DOS

"lives"

entirely

inside

the

disk

drive,

and

does

not

require

any

internal

memory

in

the

computer

to

do

its

work,

nor

does

it

have

to

be

loaded

before

use

like

DOS

on

other

computers.

It

is

so

independent

that

once

it

begins

working

onacommand,

it

will

complete

it

while

the

computer

goes

on

to

some

other

task,

effectively

allowing

you

to

do

two

thingsatonce.

Another

key

advantage

of

the

Commodore

1541

over

disk

drives

for

other

computers

is

its

dynamic

allocation

of

disk

space.

Many

other

disk

drives

make

you

think

about

every

program

you

save.

Where

canIstore

it

on

this

diskette,

and

should

I

pack

the

disk

first?

(Packingisthe

processofmoving

all

the

leftover

work

areastothe

endofthe

diskette's

storage

space.)

All

thisishandled

automatically

on

Commodore

disk

drives.

The

1541

disk

drive

always

knows

where

the

will

go,

and

automatically

fits

it

into

the

best

available

spot.

Diskettes

created

on

the

1541

may

be

read

by

several

other

Commodore

disk

drives,

including

the

former

1540,

2040,

and

4040,

and

the

2031.

It

is

usually

possi

ble,

though

not

recommended,

to

write

data

to

any

one

of

these

drives

from

any

of

the

others.

The

1541

communicates

with

the

computer

and

other

devices

overacable

and

interface

knownasthe

Commodore

serial

bus.Itis

patterned

after

the

IEEE-488

bus

used

on

Commodore's

PET

and

CBM

models,

except

that

the

serial

version

only

uses

one

wire

for

data.

The

two

serial

ports

on

the

1541

allow

several

devices

to

be

connected

together

at

once,

each

plugged

into

the

*'daisy

chain"

fash

ion.Upto4disk

drives

and2printers

canbeconnected

this

way.

HOW

TO

USE

THIS

BOOK

This

bookisdivided

into

two

main

parts.

The

first

part

gives

you

the

information

you

needtouse

the

1541

effectively,

evenifyou

know

littleornothing

about

programming.

This

partofthe

book

tells

you

howtosetupthe

system,

howtoprepare

diskettes

for

use,

howtoreadadirectory,

and

howtoload

programs.

Part

twoofthe

bookisfor

advanced

users

and

those

who

would

liketobecome

advanced

users.

This

part

provides

more

advanced

commands,

tells

about

the

different

files

the

1541

uses,

and

howtomanage

them,aswellasgivingafew

hints

for

machine

language

programmers.

Both

beginning

and

advanced

users

will

find

valuable

information

in

the

appendi

ces—a

quick

reference

listofdisk

commands,alistofdisk

error

messages

and

what

they

mean,aglossaryofwords

usedinthis

manual,

howtouse

twoormore

disk

drives

at

once,

and

explanations

of

some

programsonthe

Test/Demo

diskette

packed

with

your

1541.

Since

ownersoffour

different

Commodore

computers

use

the

1541,wehave

separated

several

explanations

into

two

versions,

dependingonwhich

Basic

your

com

puter

uses.Ifyou

haveaVIC20or

Commodore

64,

please

read

the

pages

marked

Basic

2.

Those

with

the

Commodore16or

the

Plus/4

should

read

pages

marked

Basic

3.5.

For

many

commands,

there

will

be an

added

pageortwooffurther

comments

and

advanced

techniques.

Feel

free to

skip

anything

you

don't

understand

on

those

pages

now,

and

come

back

later.

BASIC

OPERATING

STEPS

If

you're

like

most

people,

you're

anxioustostart

using

your

new

disk

drive

(

right

away.Inviewofthat,wehave

outlined

the

basic

steps

you

needtoknow

in

ordertoget

started.

Once

you've

mastered

the

basic

steps

however,

you

will

needtorefertothe

rest

of

this

manual

in

order

to

make

full

use

of

the

1541

*s

features.

In

fact,

before

you

begin,

you

should

takealookatthe

following

short

sections,

which

offer

precautions

on

handling

the

equipment:

"Simple

maintenance

tips,"

"Safety

rules

for

diskette

care,"

and

"Safety

rules

for

removing

diskettes."

1.

Unpack,

hook-up,

and

turnonthe

disk

drive.

There'snoshortcut

through

this

part.

You'll

havetoread

this

sectiontofind

out

what

connectstowhat,

whentoturn

everything

on,

and

howtoempty

the

drive.

If

you

run

into

any

problemsatthis

point,

refertothe

Troubleshooting

Guide.

Gently

insertapre-programmed

diskette.

For

the

purposeofdemonstration,

use

the

Test/Demo

diskette

that

was

included

with

the

disk

drive.

If

you

run

into

any

problemsatthis

point,

refertoChapter2,"Inserting

a

Diskette."

3.

Type:

LOAD

"HOW

TO

USE",8

(forBasic2)

DLOAD

"HOW

TO

USE"(for

Basic

3.5)

Press:

RETURN

HOW

TO

USE

is

the

name

ofaparticular

program

on

the

Text/Demo

diskette.

To

loadadifferent

BASIC

program,

substitute

the

name

of

that

program

inside

the

quotation

marks.

If

you

want

to

loadaprogram

that

isn't

written

in

BASIC

language,

you

must

use

the

Basic2command

and

add

the

following

after,the

8

in

that

command:

,1

If

you

run

into

any

problems

at

this

point,

refer

to

Chapter

2,

the

section

enti

tled

"LoadingaPackaged

Program."

4.

After

you

perform

step3,the

following

will

appearonthe

screen:

SEARCHING

FOR

HOW

TO

USE

LOADING

READY

At

this

point,

type

RUN

and

press

the

RETURN

key

and

follow

the

directions

for

the

program.

SPECIFICATIONSOFTHE

1541

DISK

DRIVE

STORAGE

Total

formatted

capacity

174848

bytes

per

diskette

Maximum

Sequential

file

size

168656

bytes

per

diskette

Maximum

Relative

file

size

167132

bytes

per

diskette

Records

per

file

65535

Files

per

diskette

144

Tracks

per

diskette

35

Sectors

per

track

17-21

Sectors

per

diskette

683

total

664

free

for

data

Bytes

per

sector

256

INTEGRATED

CIRCUIT

CHIPS

USED

1

6502

microprocessor

Used

for

overall

control

2

6522

VIA

Versatile

Interface

Adapters

Used

for

input

and

output,

andasinternal

timers

16116

RAM

Random

Access

Memory

Usedas2Kofbuffers

1

16KROM

Read-Only

Memory

Containsa16K

Disk

Operating

System

(DOS)

INTERFACE

USED

Commodore

serial

bus

with

two

6-pin

DIN

connectors

Device

number

selectable

from

8-11

Secondary

addresses

0-15

PHYSICAL

DIMENSIONS

Height

Width

Depth

77

mm

184

mm

256

mm

ELECTRICAL

REQUIREMENTS

Three

wire-grounded

detachable

power

cable.

Voltage

U.S.

100-120

VAC

Export

220-240

VAC

Frequency

U.S.

60

HZ

Export

50

HZ

Power

used

25

Watts

MEDIA

Any

good

quality

5lA

inch

diskette

maybeused

(Commodore

diskettes

are

recom

mended).

PART

1:

GUIDE

TO

OPERATION

CHAPTER

1

DISK

DRIVE

UNPACKING

The

first

thing

you

will

needtodo

with

your

disk

driveisunpack

it.

Inside

the

carton

in

which

you

found

this

manual,

there

should

also

be: a

1541

disk

drive,

supply

power

a

black

cabletoconnect

the

disk

drivetothe

computer,

a

demonstration

diskette,

and

a

warranty

cardtobe

filled

out

and

returnedtoCommodore.

Please

don't

connect

anything

until

you've

read

the

pages!Itcould

save

youalotoftrouble.

Figl.

Front

Panel

I

POWER

I

DRIVE

[commodore

154W

I

FLOPPY

DISK

DRIVE

I

V

7

DOOR

LEVER

DRIVE

INDICATER

(GREEN

LED)

LIGHT:

ACTIVE/FLASH:

ERROR

POWER

INDICATER

(RED

LED)

•LIGHT:

POWER

ON

THE

PRODUCT

DOES

NOT

NECESSARILY

RESEMBLE

THE

PICTURE

INSIDE

THE

USER'S

MANUAL.

5

EMPTY

THE

DRIVE

First,itis

very

important

tobesure

nothingisinside the

disk

drive.Ifyou

turn

the

power

off

or

oh

withadiskette

in

the

drive,

you

could

lose

its

contents

and

have

to

re-

record

it.

Since

you

wouldn't

like

havingtodo

that,

always

checktobe

sure

nothing

is

inside

the

drive

before

turningitofforon.

When

you

first

unpack

the

disk

drive,

you

will

findacardboard

shipping spacer

inside.

Following

the

instructions

below,

pullitoutasthoughitwereadiskette,

but

don't

throwitaway.

You

will

wanttoputitback

inside

the

slot

any

time

you

moveorship

the

disk

drive

later.

To

check

whether

the

driveisempty

(Fig.

1),

simply

rotate

the

leveronthe

front

of

the

disk

drive

counter-clockwise

untilitstops,

one-quarter

turnatmost.

Then

reach

inside

the

long

slot

the

lever

covers

whenitpoints

down,

and

pull

out

any

diskette

you

find

there.

CONNECTING

THE

CABLES

With

the

power

supply,

the

power

cable

plugs

into

the

backofthe

disk

driveatone

end,

and

intoagrounded

(3-prong)

outletatthe

other

end.It

will

onlygoin

one

way.

Before

you

plugitin

though,

make

sure

that

your

entire

computer

systemisturned

off.

The

disk

drive's

on/off

switchisin

the

back,onthe

right

side

(when

viewed

from

the

back).Itis

off

when

the

botton

halfispushed

inward.

Leave

your

whole

system

off

until

everything

is

connected.Wewill

tell

you

whenitis

safe

to turniton.

Fig

2.

Back

Panel

DIP

SWITCH

FOR

CHANGING

POWER

SWITCH

DEVICE

NUMBER

SERIAL

INTERFACE

POWER

ON/OFF

ON

1

SERIAL

PORT

OFF

0

POWER

CORD

SOCKET

CONNECTORS

FOR

INTERFACE

CABLES

After

plugging the

power

supply

into

the

disk

drive

andasuitable

outlet,

find

the

black

cable

that

goes

from

the

disk

drivetothe

computer.Itis

calledaserial

bus

cable

to

describe

the

way

the

computer,

and

other

accessories

communicate

with

each

other

through

its

wires.Ithasanidentical

6-pin

DIN

connectorateach

end,

which

like

the

power

connector

can

onlygoin

one

way—with

the

dimpleinthe

sideofthe

plug

facing

up.

To

pluginthe

serial

bus

cable,

find

the

dimpleonthe

sideofthe

metal

partofthe

plug

and

turn

that

side

up.

Then

pushitstraight

into

oneofthe

two

serial

bus

connectors

on

the

backofthe

disk

drive.

The

other

end

goes

into

the

similar

connectoronthe

back

of

your

computer,

marked

'*serial

bus."Ifanother

accessory,

suchasa

printer,isalready

connected

there,

unplug

the

other

device's

cable

from

the

computer,

and

attachitto

the

spare

serial

bus

connectoronthe

backofthe

1541.

Then

install

the

serial

cable

from

the

1541inthe

serial

bus

connectoronthe

backofthe

computer

(Fig

3.A.)

If

you

have

more

than

one

disk

drive,

each

added

disk

drive's

serial

bus

cable

is

plugged

into

the

second

serial

bus

connectoronthe

backofthe

drive,

like

a

daisy

chain

(Fig

3.B).

However,

don't

connect

the

other(s)

until

you've

learned

how

to

change

their

device

numbers,asno

two

disk

drives

can

have

the

same

device

number.

We'll

cover

waysofchanging

disk

device

numbersinAppendixA.Until

you

are

ready

to

read

that

section,

you

may

finditeasiertoleave

your

extra

drive(s)

unconnected.

TURNINGONTHE

POWER

With

everything

hooked

up,

and

the

disk

drive

empty,itis

timetoturnonthe

power.

You

can

turnonthe

powertothe

disk

and

other

devicesonthe

serial

bus

(connected

via

serial

cables)inany

order

you

like.

Justbesuretoeither

turnonthe

powertothe

computer

itself

last,orto.

use a

multiple

outlet

power

box

withamaster

switchtoturn

everything

off

andonat

once.

When

everything

is

on,

including

the

computer,

the

disk

drive

will

go

throughaself

check

forasecondorso, tobesureitis

working

correctly.

After

the

drive

is

satisfied

with

its

own

health,itwill

flash

the

green

light

once,

and

the

red

power-on

light

will

glow

continuously.Atthe

same

time,

the

computer

willbegoing

throughasimilar

self-test,

and

displaying

its

hello

messageonyourTVor

video

monitor.

Once

the

green

lightonthe

disk

drive

has

flashed

and

gone

out,itis

safetobegin

working

with

the

drive.

If

the

light

doesn'tgoout,

but

continuestoflash,

you

may

haveaproblem.

Refertothe

troubleshooting

guide

for

help.

Commodore

Personal

Computer

Single

Fig

3.A

Floppy

Disc

Hookup

Printer

1541-11

Single

Drive

Floppy

Disk

Power

supply

Printer

Twin

Fig

3.B

Floppy

Disc

Hookup

Power

supply

1541-11

Single

Drive

Floppy

Disk

Commodore

Personal

Computer

lAC

TROUBLESHOOTING

GUIDE

Symptom

Red

indicator

light

on

the

1541

not

on

Cause

Disk

drive

not

turned

on

Power

supply

not

plugged

in

Power

off

to

wall

outlet

Remedy

Make

sure

power

switch

isinthe

"on"

position

Check

both

cordsofpower

cabletobe

sure

they

are

fully

inserted

Replace

fuseorreset

circuit

breakerinhouse

Green

error

light

The

disk

drive

is

Turn

the

system'off

for

on

anve

Hashes

failing

its

power-on

a

minute

and

try

again,

continously

on

self-test

Ifitrepeats,

try

again

power-up,

before

with

the

serial

bus

any

disk

commands

disconnected.

If

it

have

been

given

still

repeats,

call

your

dealer.Ifunplugging

the

serial

cable

made

a

difference,

check

the

cable

for

proper

connection

at

both

ends.

This

can

alsobecaused

by

some

cartridges

on

the

C-64

and

always

by

a

16K

cartridgeonthe

VIC

20.

Remove

the

cartridge

and

power-up

the

disk

drive

again

to

determine

where

the

problem

is.

(The

principle

behind

unplugging

the

serial

cableis"divide

and

conquer.'1

The

drive

candoits

power-on

test

even

when

not

connectedtoa

computer.Ifit

succeeds

that

way,

then

the

problem

is

probablyinthe

cableorthe

restofthe

system,

not

the

1541.)

TROUBLESHOOTING

GUIDE

Symptom

Cause

Program's

won't

load,

and

computer

says

"DEVICE

NOT

PRESENT

ERROR.''

Programs

won't

load,

but

computer

and

disk

drive

givenoerror

message.

Serial

bus

cable

not

well

connected,

or

disk

not

turned

on.

Another

deviceonthe

serial

bus

may

be

interfering.

Be

sure

serial

bus

cable

is

correctly

inserted

and

disk

driveisturned

on

Unplug

all

other

devices

on

the

serial

bus.

If

that

cures

it,

plug

them

in

oneata

time.

The

one

just

added

when

the

trouble

repeatsismost

likely

the

problem.

Also,

tryingtoload

a

machine

language

program

into

BASIC

space

will

cause

this

problem.

(Such

devices

may

notbeturnedonproperly,

or

may

have

conflicting

device

numbers.

Only

one

deviceonthe

bus

can

have

any

one

device

number.)

Programs

won't

load

and

disk

error

light

flashes.

A

disk

error

has

occurred.

Check

the

disk

error

channeltosee

why

the

error

occurred.

Follow

the

adviceinAppendix

B

to

correct

it.

(Be

suretospell

program

names

exactly

right,

as the

disk

driveisvery

particular,

even

about

spaces

and

punctuation

marks,

and

will

not

loadaprogram

unless

you

callitexactly

the

same

thingitwas

called

whenitwas

savedonthe

diskette.)

Your

own

programs

Load

fine,

but

commercial

programs

and

those

from

other

1541

owners

failtoload.

Either

the

diskette

you

are

loadingisfaulty,

(some

mass-produced

diskettes

are)oryour

disk

driveismisaligned.

Try

another

copyofthe

troublesome

programs.

If

several

programs

from

several

sources

always

failtoload,

have

your

dealer

align

your

disk

drive.

Your

own

programs

that

usedtoLoad

won't

any

more,

but

programs

savedonnewly-formatted

diskettes

still

work.

Older

diskettes

have

been

damaged.

The

disk

drive

has

gone

outofalignment.

See

the

sectiononsafety

rules

for

diskette

care.

Recopy

from

backups.

Have

your

dealer

align

your

disk

drive.

The

disk

drive

powers

up

with

the

activity

light

blinking.

Hardware

failure

(RAM,

ROM,

PCB).

Have

your

dealer

send

it

out

for

repair.

10

SIMPLE

MAINTENANCE

TIPS

Your

1541

should

serve

you

well

for

yearstocome,

but

there

areafew

things

you

candoto

avoid

costly

maintenance.

1.

Keep

the

drive

well-ventilated.

Likearefrigerator,

it

needsafew

inchesofair

circulation

on

all

sidestowork

properly.

2.

Use

only

good

quality

diskettes.

Badly-made

diskettes

could

cause

increased

wear

on

the

drive's

read/write

head.Ifa

particular

diskette

is

unusually

noisyinuse,itis

probably

causing

added

wear,

and

shouldbereplaced.

3.

Avoid

using

programs

that

"thump"

the

driveasthey

load.

Many

commercial

programs,

and

diskettes

that

are

failing,

cause

the

disk

drivetomakeabumping

or

chattering

noiseasit

attemptstoreadabad

sector.

If

the

diskette

canbecopiedtoa

fresh

diskette,

dosoimmediately.

Ifitis

protected

by

its

maker

against

copying,

the

thumping

is

intentional

and

will

havetobe

endured.Beaware,

however,

that

excessive

thumping,

especially

when

the

driveishot,

caused

some

older

1541'stogo

outofalignment

and

led

to

costly

repairs.

Current

1541's

have been

redesigned

to

prevent

the

problem.

Note:

the

"Memory-Write"

exampleinChapter8temporarily

turns

off

the

bumps.

4.Itwouldbea

good

ideatohave your

1541

checked

over

about

onceayearinnormal

use.

Several

items

are

likelytoneed

attention:

the

felt

load

padonthe

read/write

head

may

be

dirty

enoughtoneed

replacement,

the

head

itself

may

needabitofcleaning

(with

91%

isopropyl

alcoholona

cotton

swab),

the

rails

along

which

the

head

moves

may

need

lubrication

(with a

special

Molybdenum

lubricant,

NOT

oil),

and

the

write

protect

sensor

may

needtobe

dustedtobe

sure

its

optical

sensor

hasaclear

view.

Since

mostofthese

chores

require

special

materialsorparts,itis

besttoleave

the

worktoan

authorized

Commodore

service

center.Ifyou

wishtodo

the

work

yourself,

ask

your

dealertoorder

the

1541

maintenance

guide

for

you

(part

number

990445),

butbeaware

that

home

repair

of

the

1541

will

void

your

warranty.

11

CHAPTER

2

DISKETTES

WHAT

ISADISKETTE?

Beforeweactually

begin

using

the

drive,

let's

takeamomenttolookatthe

Test/Demo

diskette

packed

with

the

disk

drive.Todo

this,

graspitby

the

label,

which

shouldbesticking

outofthe

paper

jacket.

Then

pullitoutofthe

jacket

which

keepsitfree

of

dust

and

other

contaminants.

(Save

the

jacket;

the

diskette

should

alwaysbekeptinits

jacket

except

when

actually

in

useinthe

disk

drive.)Itis

often

calledafloppy

diskette,

becauseitis

flexible,

even

thoughitis

not

safetobend

diskettes.

A

diskette

is

much

likeacassette

tape,

butinthe

formofa

circle

and

enclosed

within

a

protective

square

plastic

cover.Asonacassette

tape,

onlyasmall

exposed

portion

of

the

magnetic

recording

surfaceissensitive.

You

may

touch

the

restofthe

diskette

any

time

you

like,

but

avoid

touching

the

few

small

portions

that

are

not

coveredbythe

protective

cover.

Also,

never

trytoremove

this

cover.

Unlike

the

paper

jacket,

the

plastic

diskette

coverisintendedtoremainonpermanently.

Next,

notice

the

notchonone

sideofthe

diskette

(it

maybecoveredbya

piece

of

tape).

This

notchiscalled

the

write

protect

notch.

Whenitis

covered

with

the

opaque

tape

packed

with

blank

diskettes,

the

disk

drive

cannot

change

the

contentsofthat

diskette.

Never

remove

the

tapeonthe

Test/Demo

diskette.

The

labelonthe

topofthe

diskette

says

"1541

Test/Demo"onit,

and

tells

you

which

diskette

you

are

using.

Blank

diskettes

come

with

extra

labelsinaddition

to

one

appliedbythe

makerofthe

diskette.

Use

themtodescribe

your

own

diskettes.

<*Atleast

two

other

partsofthe

diskette

are

worth

mentioning:

The

hub

and

the

access

slot.

The

holeinthe

centeriscalled

the

hub.Acone-shaped

spindle

fillsitwhen

the

drive

doorisclosed,

and

its

edges

are

clamped.

This

keeps

them

from

slipping,

when

the

diskette

spinsat300

RPMinuse.

The

oval

openinginthe

diskette

opposite

the

labeliscalled

the

access

slot.Itexposes

just

enoughofthe

diskette's

surface

for

the

read/write

head

and

load

pad

inside

the drive

to

touchaone

inch

long

line

from

the centertothe

edgeofthe

diskette's

working

surface.

The

bottom

sideofthat

slotiswhere

all

the

information

is

writtenasthe

diskette

spins.

It

is

one

place

your

fingers

should

never

touch.

ACCESS

SLOT

HUB

WRITE

PROTECT

NOTCH

WHEN

COVERED,

DISKETTE

CONTENTS

CANNOT

BE

ALTERED

LABEL

Fig.4.

Position

for

Diskette

Insertion

12

SAFETY

RULES

FOR

DISKETTE

CARE

1.

Keep

the

disk

drive

and

its

diskettes

away

from

all

moisture,

dust,

smoke,

food,

and

magnets

(including

the

electromagnets

in

telephones

and

TV's).

Also

keep

them

away

from

temperatures

either

too

hotortoo cold

for

youtoworkinfor

extended

periods.

2.

When

notinthe

drive,

diskettes

shouldbestored

upright

inside

their

paper

jackets.

Do

not

allow

themtobecome

bentorfolded.

Since

the

working

partofthe

diskette

is

on

the

bottom,

never

setitdownona

table

top,orother

place

where

dustormoisture

might

affect

it,

andbeespecially

carefultokeep

your

fingers

away

from

the

openings

in

the

diskette

cover.

3.

Although

some

people

sell

kits

intendedto"double

your

diskette's

capacity"

by

cuttinganextra

write-protect

notch

intoadiskette,

itisbest

nottouse

the

other

side

of

the

diskette

on

the

1541

drive,

evenifyour

diskette

is

labeled

"double-sided."

Doing

so

will

cause

added

weartoyour

diskettes

and

drive,

and

may

cost

youanimportant

program

some

day.

4.

When

buying

diskettes,

you

may

use

any

good

quality

5lA

inch

diskette.

5.

Make

sure

the

diskette

center

holeismoreorless

centeredinits

opening

before

inserting

the

diskette

into

the

drive.

Although

the

hub

assembly

will

correctly

center

most

any

diskette,

it

wouldbevery

difficult

to

rescue

data

fromadiskette

recorded

with

its

hub

off-center.

One

waytohelp

center

diskettes

isto"tickle"

the

drive

door

shut

insteadofslammingitdown.Bygently

closing

it

part-way,

and

then

openingabit

and

then

closing

the

restofthe

way,

you

give

the

spindle

more

chancestocenter

the

diskette

properly.

Another

waytoease

diskette

centering

istobuy

diskettes

that

come

with

reinforced

hubs.

These

hard

plastic

rings

around

the

hub

opening

make

the

diskette

hub

more

rigid,

and

easiertocenter

properly.

INSERTINGADISKETTE

To

insertadisketteina

1541

(Fig.

1),

first

open

the

drive

doorbyrotating

the

door

lever

counter-clockwise

one

quarter

turn

untilitstops,

with

the

lever

level

with

the

slot

in

the

frontofthe

drive.

Grasp

the

diskettebythe

side

opposite

the

large

oval

access

slot,

and

holditwith

the

labelupand

the

write-protect

notchtothe

left.

Now

insert

the

diskettebypushing

it

straight

into

the

slot,

the

access

slot

goinginfirst

and

the

label

last.Besure

the

diskette

goesinuntilitstops

naturally,

withnopart

showing

outside

the

drive,

but

you

shouldn't

havetoforceorbenditto

getitthere.

With

the

disketteinposition,

seatitproperly

for

usebytwisting

the

door

lever

clockwise

one-quarter

turn,

vertically

over

the

slot

untilitstops.Ifit

does

not

move

easily,

stop!

You may

have

put

the

diskette

in

the

wrong

way,orincompletely.

If

that

happens,

reposition

the

diskette

until

the

door

lever

closes

easily.

13

SAFETY

RULES

FOR

REMOVING

DISKETTES

Always

remove

diskettes

before

turningadrive

offoron.Ifa

diskette

wereinplace

and

the

door

closedatpoweronor

off,

you

could

lose

partorallofthe

dataonthat

diskette.

Similarly,

do

not

removeadiskette

from

its

drive

when

the green

drive

activity

light

is

on!

That

light

only

glows

when

the

driveisactually

in

use.

Removing

the

diskette

with

it

on

may

resultinyour

losing

information

currently

being

writtentothe

diskette.

LOADINGAPACKAGED

PROGRAM

To

use

prepackaged

BASIC

programs

available

on

diskette,

hereisthe

procedure:

After

turningonyour

computer

system,

carefully

insert

the

preprogrammed

diskette

as

describedonthe

For

purposeofdemonstration,

use

the

Test/Demo

diskette

included

with

the

disk

drive.

The

following

commands

will

loadaprogram

from

the

diskette

into

the

computer:

BASIC

2:

LOAD

"program

name",device

number,relocate

flag

Example:

LOAD

"HOW

TO

USE",8

BASIC3.5:

DLOAD

"program

name",Ddrive

#,Udevice

number,relocate

flag

Example:

DLOAD

"HOW

TO

USE"

After

each

command

press

the

RETURN

key

In

both

cases

the

exact

nameofthe

program

wantedisplaced

between

quotation

marks.Drive#is

optional.

Nextisthe

device

numberofyour

disk

drive

which,

unless

you

change

it,isalways

8

on

the

1541.Ifyou

have

more

than

one

drive

however,

you

will

needtochange

the

device

numberonany

additional

drive

(see

AppendixAfor

instructions

on

setting

a

drive's

device

number).

14

Lastisthe

relocate

flag.Itcan

have

oneoftwo

values,0and1.If

the

relocate

flag

is

0oromitted,

all

Commodore

computers

that

use

the

1541

automatically

relocate

the

programs

they

loadtoliveinthe

partofcomputer

memory

reserved

for

BASIC

programs.

If

the

relocate

flag

valueis1,

auto-relocation

is

turned

off,

and

the

programisloaded

into

the

exact

partofmemory

from

whichitwas

originally

saved.

This

feature

allows

machine-language

and

other

special

purpose

programstocome

into

the

computer

at

the

correct

location

for

themtooperate

properly.Atthis

pointinyour

learning,

the

only

thing

you

needtoknow

about

the

relocate

flagishowtouse

it.

Simply

include

the1at

the

endofthe

LOAD

commandifa

particular

program

doesn't

run

properly

when

loaded

the

usual

way.

After

you

typeinthe

command

and

press

the

RETURN

key,

the

fallowing

will

appearonthe

screen:

SEARCHING

FOR

"HOW

TO

USE"

LOADING

READY.

When

the

word

READY

and

the

flashing

cursor

reappearonthe

screen

and

the

green

light

goes

offonthe

drive,

the

program

named

"HOW

TO

USE"onthe

Test/Demo

diskette

has

been

loaded

into

the

computer.Touse

it,

just

type

the

word

RUN

and

press

the

RETURN

key.

The

same Load

command

will

also

allow

youtoload

other

prepackaged

programs

from

the

Test/Demoorother

diskettes.

Merely

substitute

the

exact

program

name

that

you

wanttouse

between

the

quotation

marksinthe

above

example,

and

that

willbethe

program

the

computer

will

load(alistofTest/Demo

programsisshowninChapter3,in

the

section

entitled

"WhataDirectory

Shows").

Note:

here

andinthe

remainderofthe

book,wewill

assume you

areingraphic

mode,

seeing

upper

case

letters

and

graphic

characters

when

you

type.

Thisisthe

normal

condition

of

all

Commodore

computers

coveredbythis

manual

when

they

are

first

turned

on.Ifyou

now

see

lower-case

letters

when

you

type

without

using

the

SHIFT

key,

you

are

in

text

mode

instead.

Press

the

COMMODORE

key

(Q:),atthe

lower

left

cornerofyour

keyboard,

together

with a

SHIFT

keytoswitchtographic

mode.

HOW

TO

PREPAREANEW

DISKETTE:

BASIC

2

A

diskette

needsapatternofmagnetic

groovesinorder

for

the

drive's

read/write

headtofind

thingsonit.

This

patternisnotonyour

diskettes

when

you

buy

them,

but

addingittoadisketteissimple

once

you

knowtodo

it.

Hereisthe

procedure:

FORMAT

FOR

THE

DISK

NEW

COMMAND

OPEN

15,device

#,15,"Ndrive

#:diskette

name,id"

CLOSE

15

This

Open

command

willbedescribed

more

fully in

Chapters

4

and5.For

now,

just

copyitas

is,

replacing

only

the

parts

giveninlower

case.

These

include:

the

device

15

numberofthe

1541,

normally8;the

drive

number,

always0on

the

1541;

any

desired

name

for

the

diskette,

upto16

characters

in

length,

followedbya2character

diskette

ID

number.

The

Close

command

is

often

optional;

just

don't

Open

that

same

file

again

without

Closingitthe

first

time.

EXAMPLE:

OPEN

15,8,15,"N0:MY

FIRST

DISK,01":

CLOSE

15

Note:

the

chattering

or

thumping

noise

you

hear

just

after

the

disk

New

command

beginsisentirely

normal.

The

disk

mustbesureitisattrack1,whichitassures

by

stepping

outward45times

(ona35

track

diskette.)

The

noise

you

hearisthe

head

assembly

hitting

the

track1bumper

after

its

inevitable

arrival.

HOW

TO

PREPAREANEW

DISKETTE:

BASIC

3.5

A

diskette

needsapatternofmagnetic

groovesinorder

for

the

drive's

read/write

headtofind

thingsonit.

This

patternisnotonyour

diskettes

when

you

buy

them,

but

addingittoadiskette

is

simple

once

you

knowtodo

it.

Hereisthe

procedure:

FORMAT

FOR

THE

HEADER

COMMAND

HEADER'diskette

name''

,Iid,Ddrive

#

,Udevice

#

Where

"diskette

name"isany

desired

name

for

the

diskette,

upto16

characters

in

length;

"id"isa2character

disketteIDnumber;

"drive#"is

the

drive

number, 0

if

omitted

(asitmustbeon

the

1541);

and

"device#"is

the

disk's

device

number,

assumed

tobe8ifomitted.Asdescribedinthe

"id"isoptionalif(and

only

if)

the

diskette

has

been

previously

formattedona

1541.

Also,

theIDmustbea

string

literal,

not

a

variableorexpression,

and

may

not

include

Basic

reserved

words.

Thus,

",IFI"

cannot

be

used

becauseIfisaBasic

keyword,

and

",I(A$)"isnot

allowed

becauseA$is

a

variable.

",IA$"isallowed,

but

theIDnumber

willbethe

letter

"A"

plusadollar

sign

($),

not

the

contents

of

the

variable

A$.Ifyou

needavariable

ID

number,

use

the

Basic

2

formofthe

format

command.

EXAMPLE:

HEADER

"MY

FIRST

DISK,I01,DO"

Note:

the

chattering

or

thumping

noise

you

hear

just

after

the

Header

command

beginsisentirely

normal.

The

disk

mustbesureitisattrack1,whichitassures

by

stepping

outward45times

(ona35

track

diskette).

The

noise

you

hearisthe

head

assembly

hitting

the track1bumper

after

its

inevitable

.arrival.

REUSINGANOLD

DISKETTE

After

you

have

once

formatted

a

particular

diskette,

you

can

re-format

itasthough

it

were

brand

newatany

time,

using

the

above

procedures.

However,

you

can

also

change

its

name

and

erase

its

programs

more

quickly

and

easilybyomitting

theIDnumber

in

16

your

format

command.Byleaving

off

theIDnumber,

the

format

command

will

finishina

few

seconds

insteadofthe

usual90seconds.

ORGANIZINGADISKETTE

LIBRARY

Though

you

may

not

believe

it

now,

you

will

eventually

have

dozens,

if

not

hundreds

of

diskettes.

You

can

ease

life

thenbyplanning

now.

Assign

each

diskette

a

unique

ID

number

when

you

format

it.

There

are

diskette

cataloging

programs

you

can

buy,

that

store

and

alphabetize

a

listofall

your

file

names,

but

areoflimited

value

unless

your

disketteIDnumbers

are

unique.

At

least

two

valid

approaches

are

usedinassigning

ID

numbers.

One

startsat00

with

the

first

diskette,

and

continues

upward

with

each

new

diskette,

through

99,

and

then

onward

fromAA

through

ZZ.

Another

organizes

diskettes

within

small

categories,

and

starts

theIDnumber

for

each

diskette

in

that

directory

in

Basic2,itisusually

necessary

to

load

it,

likeaprogram.

As

when

you

load

other

programs,

this

erases

anything

alreadyinBasic

memory,sobe

sure

to

save

any

work

you

don't

wanttolose

before

loading

the

directory

in

Basic2.(Chapter

4

describes

howtoSave

a program.)

For

example,toload

the

entire

directory

from

disk

device8,type:

LOAD'T',8

Then,todisplay*the

directoryonyour

screen

afteritloads

into

computer

memory,

type

LIST.

You

may

slow

the

listingbypressing

the

CONTROL

keyonthe

VIC20and

Commodore

64,

and

haltitentirelybypressing

the

STOP

key.

You

can

also

use

this

commandtolimit

the

directory

to

desired

filesbyusing

pattern-

matching

characters

described

laterinthis

chapter.

VIEWING

THE

DIRECTORY:

BASIC

3.5

To

view

the

directory

in

Basic

3.5,

simply

type

the

word

DIRECTORYona

blank

line,

and

press

the

RETURN

key.

Unlike

Basic

2's

methodofloadingadirectory,

this

does

not

erase

anything

alreadyinBasic

memory,soyou

can

safely

ask

foradirectory

at

almost

any

time,

even

from

within

another

program.

Again,

you

may

slowadirectory

listingonthe

Commodore16and

Plus/4byholding

down

the

COMMODORE

key(Ql),or

haltitentirely

by

pressing

the

STOP

key.

You

may

also

pauseitwith

CONTROL-S

(by

holding

down

the

CONTROL

key

while

pressing

the.

"S"

key),

and

resume by

pressing

any

other

key.

WHATADIRECTORY

SHOWS

Now

let's

lookatatypical

directoryonyour

1541

Test/Demo

Diskette.

18

READY.

14

IS

12

4

1

4

S

4

6

4

14

9

S

7

10

7

30

35

8

7

9

10

•

•HOW

TO

USE"

■HOW

PART

Em

•HOW

PART

3"

■VIC-20

WEDGE"

■C-64

WEDGE*

■DOS

3.I"

•PRINTER

TEST"

"DISK

ADDR

CHANGE"

■VIEW

BAM"

■CHECK

DISK"

■DISPLAY,

T&SW

■PERFORMANCE

TEST"

"SEQ.FILE.DEMO"

■SO.BACKUP.C16"

■SD.BACKUP.PLUS4"

■SD.BACKUP.C64"

"PRINT.64.UTIL"

■PRINT.C16.UTIL"

■PRINT.44.UTIL"

■C64

BASIC

DEMO"

"44

BASIC

DEMO"

■LOAD

ADDRESS-

■UNSCRATCH"

■HEADER

CHANGE"

"REL.FILE.DEMO"

PRG

IMPORTANT

NOTE:

Your

Test/Demo

diskette

may

contain

additional

programs.

Commodore

may

update

the

diskette

from

time

to

time.

426

BLOCKS

FREE.

Starting

with

the

top

line,

hereiswhatittells

us:

The0at

the

left

end

tellsusthat

the

1541's

single

driveisdrive0.Ifwehad

gotten

this

directory

fromadual

disk

drive,itmight

have

said

"1"

instead.

The

top

lineofthe

directory

after

the

format

typeisthe

nameofthe

diskette,

enclosedinquotation

marks,

and

printedinreverse

field.

Justaseach

program

hasaname,sodoes

the

diskette

itself,

assigned

when

the

diskette

was

formatted.

The

diskette

name

maybeupto16

characters

long,

and

serves

mainlytohelp

you

organize

your

diskette

library.

By

keeping

together

on

the

same

diskette,

you'll

ease

the

taskoffinding

the

program

you

want

later,

when

you

have

dozensorhundreds

of

diskettes.

The

two

character

code

to

the

right

of

the

name

is

the

diskette

ID,

also

created

when

the

diskette

was

formatted,

and

equally

useful

for

individualizing

diskettes.

The2Aat

the

right

endofthe

top

line

tellsusthat

the

1541

uses

version2of

Commodore's

DOS

(disk

operating

system),

and

that

it,

like

most

Commodore

drives,

uses

format

"A."

19

The

restofthe

directory

contains

one

line

per

programorfile,

each

line

supplying

three

piecesofinformation

about

its

subject.

At

the

left

endofeach

lineisthe

sizeofthat

line's

fileinblocks

(or

sectors)

of

256

characters.

Four

blocks

are

equivalent

toIK(1024

characters)

of

RAM

(read/write)

memory

inside

the

computer.

The

middleofeach

directory

line

contains

the

nameofthe

file,

enclosedinquotation

marks.

All

characters

between

the

quote

marks

are

partofthe

name,

and

mustbeincluded

when

loadingoropening

that

file.

The

right

portionofeach

directory

lineisa

three

character

abbreviation

for

the

file

typeofthat

entry.Aswe

will

see

in later

chapters,

there

are

many

waystostore

information

onadiskette,

mostofwhich

are

associated

withadistinctive

file

type.

TYPESOFFILES

AVAILABLE

Currently

used

file

types

include:

PRG =

Program

files

SEQ=Sequential

data

files

REL=Relative

data

files

USR=User

(nearly

identical

to

sequential)

DEL=Deleted

(you

may

never

see

oneofthese.)

(Note:

Direct

Access

files,

also

called

Random

files,donot

automatically

appear

in

the

directory.

They

are

discussed

in

Chapter

7.)

After

all

the directory

entries

have

listed,

the

directory

finishes

withamessage

showing

how

many

blocksofthe

diskette

are

still

available

for

use.

This

number

can

vary

from

664ona

new

diskette

to0on

one

thatisalready

completely

full.

WATCH

OUT

FOR

SPLAT

FILES!

One

indicator

you

may

occasionally

noticeona

directory

line,

after

you

begin

saving

programs and

files,isan

asterisk

appearing

just

before

the

file

typeofa

file

thatis0

blocks

long.

This

indicates

the

file

was

not

properly

closed

afteritwas

created,

and

that

it

should

notberelied

upon.

These

"splat"

files

(as

they

are

calledinEngland)

will

normally

needtobe

erased

from

the

diskette

and

rewritten.

However,donot

use

the

Scratch

commandtoget

ridofthem.

They

can

onlybesafely

erasedbythe

Validate

and

Collect

commands.

Oneofthese

should

normallybeused

wheneverasplat

fileisnoticed

onadiskette.

(All

these

commands

are

described

in

the

There

are

two

exceptions

to

the

above

warning:

oneisthat

Validate

and

Collect

cannotbeusedonsome

diskettes

that

include

direct

access

(random)

files,

and

the

other

is

thatifthe

information

in

the

splat

file

was

crucial

and

can'tbereplaced,

thereisa

way

to

rescue

whatever

partofthe

file

was

properly

written.

(This

optionisalso

described

in

the

20

PRINTINGADIRECTORY

To

makeapermanent

copyofa

directory,

perhapstofastentothe

diskette's

outer

(paper)

envelope,

you

will

needtosend

the

directory

toaprinter,

suchasCommodore's

MPS

801,

1520 and

1526

serial

bus

models.Todo

this,

you

may

needtorefertoyour

printer

manual,

but

briefly

the

procedure

for

listingadirectorytodevice4isasfollows:

LOAD44$0",8

OPEN

4,4:CMD

4:LIST

PRINT#4:CLOSE

4

Also

note

that

allofthe

statements

that

can be

combinedonone

line

already

have

been.

Type

theminimmediate

modetoavoid

disturbing

the

directory.

All

other

options,

suchasdiffering

device

numbers,

and

selective

directories

(see

can

alsobespecified

as

usualinthe

Load

command.

WARNING:Besuretoinclude

the

PRINT#

command

after

every

printer

listing.

Otherwise,

the

printer

will

remainasan

unwanted

listener

on

the

serial

bus,

and

may

disrupt

other

work.

Also,donot

abbreviate

PRINT#as?#.

Although

it

will

look

proper

when

listed

out,itwill

causeaSYNTAX

ERRORinuse.

The

proper

abbreviation

for

PRINT#ispR.

READINGADIRECTORYASA

FILE

If

you

would

liketoreadadirectory

from

withinaprogram,

you

maydoso.InBasic

3.5,

simply

include

the

DIRECTORY

commandinyour

Basic

program.InBasic

2,

however,

and

optionally

in

the

others,

you

will

havetoOpen

the

directory

as

though

it

were"a

data

file

and

readitcharacter

by

character.

See

the

discussion

of

Get#inChapter

5

for

more

information.

ANOTHER

WAY

TO

BE

SELECTIVE

Before

discussing

the

pattern-matching

options

available

for

useinseveral

disk

commands,

let's

cover

one

more

thatisonly

usableina

directory.

Several

different

types

of

files

can

coexist

peacefully

on^the

same

diskette.Byaltering

our

directory

load

command,wecan

createadirectory

from

the

filesofa

single

selected

type.

Thus,

we

might

requestalistofall

sequential

data

files

(see

Chapter

5),

oneofall

the

relative

data

files

(see

Chapter

6),oroneofonly

program

files.Todo

this,

simply

addtothe

end

of

your

selective

directory

request

the

equals

sign

(=)

followedbythe

first

letterofthe

file

type

you

wantinyour

directory.

For

example,

the

Basic2command:

21

LOAD"$0:*=S",8

will

load a

directory

of

all

sequential

files,

while

the

Basic

3.5

command:

DIRECTORY,4

4A*=R"

will

display

a

directory

consisting

only of

relative

files

beginning

with

the

letter

"A".

The

possible

file

types,

and

their

abbreviations

for

this

use

are:

P=Program

S=Sequential

R=Relative

U=User

D=Deleted

A=Append

M

=

Modify

PATTERN

MATCHING

AND

WILD

CARDS

Justascassette

users

can

load

programs

without

givingafull

name,

disk

users

can

use

special pattern

matching

characters

to

load a

program

fromapartial

name.

The

same

characters

can

alsobeusedtoprovide

selective

directories.

The

two

special

characters

usedinpattern

matching

are

the

asterisk

(*)

and

the

question

mark

(?).

They

act

something

likeawild

cardina

gameofcards.

The

difference

between

the

twoisthat

the

asterisk

makes

all

characters

in

and

beyond

its

position

wild,

while

the

question

mark

only

makes

its

own

character

position

wild.

Here

are

some

examples,

and

their

results:

LOAD

"A*",8

loads

the

first

fileondisk

that

begins

withan"A",

regardless

of

what

follows.

"ARTIST",

"ARTERY",

and

"AZURE"

would

all

qualify,

but

"BARRY"

wouldn't,

even

thoughithasan"A"

elsewhere

in

its

name.

DLOAD

"SM7TH"

(Basic

3.5)

loads

the

first

program

that

starts

with

"SM",

ends

with

"TH",

and

has

one

other

character

between.

This

would

load

"SMITH"

or

"SMYTH",

but

not

"SMYTHE"

OPEN

8,8,2;4R?C*,S,R"

We'll

study

OpeninChapter5,but

the

pattern

used

here

means

that

the

selected

file

will

begin

withan"R"

and

havea"C"inthe

third

character

of

its

name.

DIRECTORY,"Q*"

(Basic

3.5)

will

loadadirectory

of

files

whose

names

begin

with

"Q".

LOAD

"*",8

and

DLOAD

"*"

are

special

cases.

When

an

asterisk

is

used

alone

as

a

name,itmatches

the

last

file

used.Ifnone

have

been

used

yetonthe

current

diskette

since

turning

on

the

drive,

using

the

asterisk

alone

loads

the

first

program

on

the

diskette.

10

INPUT

A$:LOAD

A$+"*",8

loads

any

file

whose

name

starts

with

the

characters

enteredinA$.

22

FORMAT

FOR

PATTERN

MATCHING:

EXAMPLES:

"expression*"

"C-64*"

or

"expression?expression"

"C?64

WEDGE"

or

4

'expression?expression*''''C-647WED*''

Use

anyofthe

above

patternsinanyofthe

disk

commands

whose

format

includes

a

pattern.

This

appliestoLoad,

Dload,

Directory,

Open,

Scratch,

andtothe

source

file

in

the

Copy

and

Rename

commands.

More

than

one

"?"

can

appearinthe

same

pattern.

As

you

might

expect,

their

useinpattern

matching

means

you

can't

use

the

asterisk

or

question

markina

file

name

when

savingorwritingafile

(see

23

PART

TWO:

GUIDE

TO ADVANCED

OPERATION

AND

PROGRAMMING

CHAPTER

4

COMMANDS

COMMAND

CHANNEL

Commodore

disk

drives

expecttoreceive

manyoftheir

instructions

over

what

is

knownasa

command

channel.

Althoughwewill

not

explain

the

concepts

behindituntil

Chapter6,we

will

learnitto

useitnow,soyou

can

give

your

1541

disk

the

commands

it

needstodo

some

essential

chores.

To

instruct

the

command

channel,weuseaBasic

Open

statement

to

the

disk,

with

a

secondary

addressof15.

The

usual

formofthis

statement

is:

OPEN

15,8,15

The

first15isafile

number,

and

couldbeany

number

from1to

255.Itis

used

to

match

the

secondary

address

(the

last

numberonthe

line),

whichisalso

15.

The

middle

numberisthe

primary

address,

better

knownasthe

device

number,

andisnormally

8

when

talking

with

the

1541.Asecond

disk

drive

would

usuallybe9,athird,10andsoon.

Once

the

command

channel

has

been

opened,

use

the

Basic

Print#

commandtosend

information

to

the

disk

drive,

and

Basic's

Input#

commandtoreceive

information

back

from

the

disk

drive.

These

two

commands

are

like

Basic's

Print

and

Input

statements,

except

that

they

use

the

device

number

specified

in

the

preceding

Open

statement

instead

of

defaulting

to

the

screen

and

keyboard

respectively.

In

Basic2,you'll

use

both

Print#15

and

Input#15

extensively,

to

send

housekeep

ing

commandstothe

disk

andtocheck

its

error

status.

Basic

3.5

has

built-in

commands

for

mostofthese

chores.

Even

so,itwillbegood

for

thoseofydu

with

Basic

3.5tosee

how

such

commands

are

sent.

SendingaCommand

via

the

Command

Channel

Hereisthe

waywesend

the

Initialize

commandtothe

disk

via

the

command

channel.

PRINT#15,"I0"

This

command

assumes

we

have

already

opened

the

file

15

to the

command

channel.

"IO"

canbereplaced

with

any

string

expression

thatisa

valid

disk

com

mand.

If

file

15

isn't

already

open,

we

can

combine

the

Open

and

the

Print#

in

a

single

statement:

OPEN

15,8,15,<4I0"

However,

this

only

works

for

the

first

disk

command

given.

After

that,

file15is

already

open,

and

Opening

it

again

would

causea"FILE

OPEN"

error.

Added

com

mands

are

sent

via

Print#

instead.

25

FORMAT

FOR

SENDING

DISK

COMMANDS

OPEN

15,device#,15,command$

or

Print#

15,

commands

Examples:

OPEN

15,8,15,

"VO"

or

PRINT#15,"VO"

where

"device#"is

the

disk's

device

number,

normally8,and

"command$"isany

valid

string

expression.

Ifitis

not

alsoavalid

disk

command,itwill

resultinan

error

on

the

disk

drive.

Thisisindicatedbya

flashing

error

lightonthe

disk

drive,

andanerror

message

suchas"31,SYNTAX

ERROR"

when

the

error

channelisreadasdescribed

on

the

pages.

READING

THE

ERROR

CHANNEL:

BASIC

2

In

Basic2,thereisno

simple

waytolearn

whatiscausing

the

error

lighttoflash

on

the

disk

drive

without

writingasmall

program.

This,inturn,

causes

youtolose

any

program

variables

alreadyinmemory.

The

reason

for

thisisthat

the

INPUT#

command

cannot

easilybeusedinimmediate

mode

(that

is,

withoutaline

number).

You

will

often

need

to

be

able

to

read

the

disk

error

channel,

to

see

why

the

disk

error

lightisflashing,

and

thereby

turn

the

error

light

off

again.

Hereisa

brief

programtocheck

for

disk

errors:

10J3PEN

15,8,15

20

INPUT#15,EN,EM$,ET,ES

30

PRINT

EN,EM$,ET,ES

40

CLOSE

15

This

little

program

reads

the

error

channel

into4Basic

variables,

and

prints

the

results

on

the

screen.

A

message

will

be

displayed

whether

there

is

an

error

or

not,

but

if

there

was

an

error,

this

program

will

also

clear

it

from

disk

memory

and

turn

off

the

error

lightonthe

disk

drive.

Once

the

message

is

on

the

screen,

you

can

look

it

up

in

AppendixBto

see

what

it

means,

and

whattodo

about

it.

READING

THE

ERROR

CHANNEL:

BASIC

3.5

In

Basic

3.5,

it

is

very

easy

to

learn

what

is

causing

the

error

light

to

flash

on

the

disk

drive,

and

no

need

to

writeaprogram.

Simply

type:

26

PRINT DS$

or

abbreviate

it

to

?DS$

eitherinimmediate

modeorwithinaprogram,

and

the

current

error

status

messageofthe

disk

willbedisplayed

on

the

screen.

A

message

willbedisplayed

whether

thereisan

error

or

not,

butifthere

wasanerror,

printing

its

message

will

also

clearitfrom

the

disk

memory

and

turn

off

the

error

lightonthe

disk

drive.

Once

the

messageison

the

screen,

you

can

lookitupinAppendixBto

see

what

it

means,

and

whattodo

about

it.

ERROR

CHECK

SUBROUTINE

Since

thoseofyou

who

are

writing

programs

shouldbechecking

the

error

status

after

each

disk

command,

you

may

want

to

include

a

small

subroutine

in

each

program

to

take

careofthe

error

channel.

Hereisoneweuse:

Basic2version:

Basic

3.5

version:

59980

REM

READ

ERROR

CHANNEL

59990

REM

READ

ERROR

CHANNEL

59990

INPUT#15,

EN,EM$,ET,ES

60000

IF

DS>1

THEN

PRINT

DS$:STOP

60000IFEN>1THEN

PRINT

EN,EM$,ET,ES:STOP

60010

RETURN

60010

RETURN

The

Basic2version

assumes

file

15

has

already

been

opened

earlier

in

the

program,

and

thatitwillbeclosed

somewhere

elseatthe

endofthe

program.

This

subroutine

reads

the

error

channel

and

puts

the

results

into

the

named

variables.

In

the

Basic2version,

they

are

EN,

EMS,

ET,

and

ES,

which

stand

for

Error

Number,

Error

Message,

Error

Track

and

Error

Sector

respectively.

Of

the

four,

only

EM$

has

to

beastring,

and

you

could

choose

other

variable

names,

although

these

have

become

traditional

for

this

use.

The

Basic

3.5

version

subroutine

uses

the

reserved

variablesDSand

DS$

already

set

aside

for

this

purpose.

They

are

updated

automatically

by

Basic

whenever

they

are

used.

Otherwise,

the

two

versionsofthe

subroutine

are

equivalent.

Two

error

numbers

are

harmless:

0

means

everything

is

OK,

and1tells

how

many

files

were

erasedbya

Scratch

command.Ifthe

error

statusisanything

else,

line

60000

prints

the

error

message

and

halts

the

program.

After

you

have

repaired

the

damage,

you

may

then

continue

the

program

with

Basic's

Cont

command.

Because

thisisa

subroutine,

you

accessitwith

the

Basic

Gosub

command,

either

in

immediate

modeorfromaprogram.

(For

example,

"200

GOSUB

59990".)

The

Return

statement

in

line

60010

will

jump

backtoimmediate

modeorthe

in

your

program,

whicheverisappropriate.

27

HOUSEKEEPING

HINTS

Hint

#1:Itis

besttoopen

file15onceatthe

very

startofa

program,

and

only

closeitat

the

endofthe

program,

after

all

other

files

have

already

been

closed.Dothis

because

closing

the

command

channel

automatically

closes

all

other

disk

files.Byopening

once

at

the

start,

the

fileisopen

whenever

needed

for

disk

commands

elsewhere

in

the

program.

Closingitat

the

end

makes

sure

air

disk

files

are

properly

closed

without

interrupting

any

other

file

commands.

Hint

#2:IfBasic

halts

withanerror

when

you

have

files

open, Basic

aborts

them

without

closing

them

properlyonthe

disk.Toclose

them

properlyonthe

disk,

you

must

type:

OPEN

15,8,15:CLOSE15

This

opens

the

command

channel

and

immediately

closes

it,

along

with

all

other

disk

files.

Failuretocloseadisk

file

properly

bothinBasic

andonthe

disk

may

result in

losing

the

entire

file!

HINT

#3:

One

disk

error

messageisnot

alwaysanerror.

Error

73,

"CBM

DOS

2.6

1541"

will

appearifyou

read

the

disk

error

channel

before

sending

any

disk

commands

when

you

turnonyour

computer.

Thisisa

handy

waytocheck

which

versionofDOS

you

are

using.

However,ifthis

message

appears

later,

after

other

disk

commands,itmeans

thereisa

mismatch

between

the

DOS

usedtoformat

your

diskette

and

the

DOSinyour

drive.

HINT

#4:Toreset

drive,

type:

OPEN

15,8,15,"UJ"

Then

wait

until

the

drive

activity

LEDisoff

and

motor

goes

off,

then

type:

CLOSE

15.

This

also

appliestosendingaUI

+

oraUI-

SAVING

PROGRAMS:

BASIC

2

Before

you

can

saveaprogramtodiskette,

the

diskette

mustbeformatted,

as

described

earlier.

Savingtodiskette

is

just

like

savingtocassette,

except

that

the

device

numberofthe

disk

driveisnot

optional.

FORMAT

FOR

THE

SAVE

COMMAND

SAVE*'drive #:file

name*'

,device

#

where

"file

name"isany

string

expression

ofupto16characters,

precededbythe drive

number

(always0on

the

1541)

andacolon,

and

followedbythe

device

numberofthe

disk,

normally

8.

However,itwill

not

workincopying

programs

that

are

notinthe

Basic

text

area,

such

as

"DOS

5.1"

for

the

Commodore

64.

To

copy

it

and

similar

machine

language

programs,

you

will

needamachine

language

monitor

program.

Its

use

for

this

purposeisidentical

to

the

monitor

save

describedonthe

under

Basic

3.5.

28

Note:

the

"0:"atthe

startoffile

namesisa

holdover

from

the

days

when

all

Commodore

disks

had

two

drivesinthe

same

cabinet.

Although

the

1541

will

normally

defaulttodrive0(not

having

a drive

1,)itis

besttospecify

the

drive

number

whenever

savingorwritingafile.

This

avoids

potential

confusioninDOS

(the

Disk

Operating

System.)

SAVING

PROGRAMS:

BASIC

3.5

Before

you

can

saveaprogramtodiskette,

the

diskette

mustbeformatted,

as

described

earlier.

Savingtodiskette

is

just

like

savingtocassette,

except

that

the

device

numberofthe

disk

driveisnot

optional.

FORMAT

FOR

THE

DSAVE

COMMAND

DSAVE

"file

name",Ddrive

#,Udevice

#

where

"file

name"isany

string

expression

ofupto16characters,

optionally

followed

by

the

drive

number

(the

"D"

parameter,

always0on

the

1541),

and

the

device

number

of

the

disk

drive

(the

"U"

parameter).

If

omitted,

the

drive

number

defaults

to 0,

and

the

device

numberto8.

However,itwill

not

workincopying

programs

that

are

notinthe

Basic

text

area,

suchas"DOS

5.1"

for

the

Commodore

64.Tocopyitand

similar

machine

language

programs,

you

will

need

the.Scommandofthe

machine

language

monitor

built

into

the

Commodore16and

Plus/4.Toaccessabuilt-in

monitor,

type

MONITOR.Toexit-a

monitor,

typeXaloneona

line.

FORMAT

FORAMONITOR

SAVE

S''drive

#:file

name",device

#,starting

address,ending

address■+

1

where

"drive

#:"isthe

drive

number,

0 on

the

1541;

"file

name"isany

valid

file

name

upto14

characters

long

(leaving

2

for

the

drive

number

and

colon);

"device#"isatwo

digit

device

number,

normally08on

the

1541

(the

leading0is

required);

and

the

addresses

tobesaved

are

giveninHexadecimal

(base

16,)

but

withoutaleading

dollar

sign

($).

Note

that

the

ending

address

listed

mustbe1

location

beyond

the

last

location

to

be

saved.

EXAMPLE:

Hereisthe

required

syntaxtosaveacopyof"DOS

5.1"

S"0:DOS

5.1",08,CC00,CF5A

29

SAVE

WITH

REPLACE

OPTION

Ifafile

already

exists,

it

can'tbesaved

again

because

the

disk

only

allows

one

copy

of

any

given

file

name

per

diskette.

It is

possible

to

get

around

this

problem

using

the

Rename

and

Scratch

commands

described

later.

However,ifall

you

wishtodoisreplace

a

programordata

file

witharevised

version,

another

commandismore

convenient.

KnownasSave-with-replace

,or©Save,

this

option

tells

the

disktoreplace

any

file

it

findsinthe

directory

with

the

same

name,

substituting

the

new

file

for

it.

FORMAT

FOR

SAVE

WITH

REPLACE:

FORMAT

FOR

SAVE

WITH

REPLACE:

BASIC

2

BASIC

3.5

SAVE

"©Drive

#:file

name",

device#DSAVE

4<@file

name",Ddrive

#,

Udevice

#

where

all

the

parameters

are as

usual

except

for

addingaleading

"at1'

sign

(@.)

The

"0:"inthe

Basic2version,

thoughaholdover

from

earlier

dual

drivesisrequired

here.

EXAMPLES:

SAVE"@0:REVISED

PROGRAM",8

DSAVE

"©REVISED

PROGRAM"

The

actual

procedure

is

that

the

new

versionissaved

completely,

then

the

old

version

is

scratched,

and

its

directory

entry

alteredtopointtothe

new

version.

Becauseitworks

this

way,

thereislittle,

if

any,

danger

thatadisaster

suchashaving

the

power

going

off

midway

through

the

process

would

destroy

both

the

old

and

new

copiesofthe

file.

Nothing

happenstothe

old

copy

until

after

the

new

copyissaved

properly.

However,wedo

offer

one

caution—do

not

use

©Saveonan

almost-full

diskette.

Only

useitwhen

you

have

enough

roomonthe

diskette

to

holdasecond

complete

copy

of

the

program

being

replaced.

Duetothe

way

@Save

works,

both

the

old

and

new

versions

of

the

file

areondisk

simultaneously

at

one

point,asa

wayofsafeguarding

against

loss

of

the

program.Ifthereisnot

enough

room

leftondiskette

to

hold

that

second

copy,

only

as

muchofthe

new

version

willbesavedonthe

1541asthereisstill

room

for.

After

the

command

completes,

a

lookata

directory

will

show

the

new

versionispresent,

but

doesn't

occupy

enough

blockstomatch

the

copyinmemory.

Unfortunately,

the

Verify

command

(see

will

not

detect

this

problem, because

however

much

did

get

saved

will

have

been

saved

properly.

VERIFYING

PROGRAMS

Although

notasnecessary

with a

disk

driveaswithacassette,

Basic's

Verify

command

canbeusedtomake

doubly

certain

thataprogram

file

was

properly

saved

to

disk%Itworks

much

like

the

Load

command,

except

thatitonly

compares

each

character

in

the

program

against

the

equivalent

character

in

the

computer's

mem

ory,

insteadofactually

being

copied

into

memory.

30

If

the

disk

copyofthe

program

differs

evenatiny

bit

from

the

copyinmemory,

"VERIFY

ERROR"

willbedisplayed,

to

tell

you

that

the

copies

differ.

Thisinitself

doesn't

mean

either

copyisbad, butifthey

were

supposedtobe

identical,

oneorthe

other

has a

problem.

Naturally,

there'snopointintryingtoverifyadisk

copyofa

program

after

the

originalisno

longerinmemory.

With

nothingtocompare

to,anapparent

error

will

always be announced,

even

though

the

disk

copyisalways

and

automatically

verified

as

it

is

writtentothe

disk.

FORMAT

FOR

THE

VERIFY

COMMAND:

VERIFY

"drive

#:pattern",device

#,

relocate

flag

where

"drive

#:"isan

optional

drive

number(0on

the

1541,)

"pattern"isany

string

expression

that

evaluates

toafile

name,

withorwithout

pattern-matching

characters,

and

"device#"is

the

disk

device

number,

normally8.If

the

relocate

flagispresent

and

equals1,the

file

willbeverified

where

originally

saved,

rather

than

relocated

into

the

Basic

text

area.

A

useful

alternate

formofthe

command

is:

VERIFY

"*",device#

It

verifies

the

last

file

used

without

havingtotype

its

nameordrive

number.

However,

it

won't

work

properly

after

save-with-replace,

because

the

last

file

used

was

the

one

deleted,

and

the

drive

will

trytocompare

the

deleted

filetothe

programinmemory.

No

harm

will

result,

but

"VERIFY

ERROR"

will

alwaysbeannounced.Touse

verify

after

@SAVE,

includeatleast

partofthe

file

name

thatistobeverified

in

the

pattern.

One

other note

about

Verify—when

you

Verifyarelocated

file,anerror

will

nearly

alwaysbeannounced,

duetochangesinthe

link

pointers

of

Basic

programs

made

during

relocation.

Itisbesttoonly

verify

files

saved

from

the

same

typeofmachine,

and

identical

memory

size.

For

example,aBasic

program

saved

fromaVIC20can't

easily

be

verified

usingaCommodore

64,

even

when

the

program

would

work

fineonboth

machines

(unless

the

programisre-saved).

This

shouldn't

matter,asthe

only

time

you'll

be

verifying

filesonmachines

other

than

the

one

which

wrote

themiswhen

you

are

comparing

two

disk

filestoseeifthey

are the

same.

Thisisdonebyloading

one

and

verifying

against

the

other,

andassuggested,

can

onlybedoneonthe

same

machine

and

memory

sizeasthe

oneonwhich

the

files

were

first

created.

ERASING

OLD

PROGRAMS:

BASIC

2

The

Scratch

command

allows

youtoerase

unwanted

files,

and

free

the

space

they

occupied

for

usebyother

files.Itcanbeusedtoerase

eitherasingle

file,orseveral

files

at

once

via

pattern-matching.

31

FORMAT

FOR

THE

SCRATCH

COMMAND:

PRINT#

15,'

'SCRATCHO:pattern''

or

abbreviate

it

as:

PRINT#15,"S0:pattern"

"pattern"

can

be

any

file

name

or

combination

of

characters

and

wild

card

characters.

As

usual,

it

is

assumed

that

the

command

channel

has

already

been

opened

as

file

15.

Although

not

absolutely

necessary,

it

is

best

to

include

the

drive

number

in

Scratch

commands.

If

you

check

the

error

channel

afteraScratch

command,

as

described

in

the

prior

section,

the

value

for

ET

(error

track)

will

tell

you

how

many

files

were

scratched.

For

example,

if

your

diskette

contains

program

files

named

"TEST",

"TRAIN",

"TRUCK",

and

"TAIL",

you

may

scratch

all

four,

along

with

any

other

files

beginning

with

the

letter

"T",byusing

the

command:

PRINT#15,"S0:T*"

Then,toprove

they

are

gone,

you

can

type:

GOSUB

59990

to

call

the

error

checking

subroutine

given

earlier

in

this

chapter,

andifthe

four

listed

were

the

only

files

beginning

with

"T",

you

will

see:

01,FILES

SCRATCHED,04,00

READY.

■

The

"04"

tells

you4files

were

scratched.

ERASING

OLD

PROGRAMS:

BASIC

3.5

The

Scratch

command

allows

you

to

erase

unwanted

programs

and

files

from

your

diskettes,

and

free

up

the

space

they

occupied

for

use

by

other

files

and

programs.

It

can

be

usedtoerase

eitherasingle

file,orseveral

filesatonce

via

pattern-matching

(described

at

the

endofChapter

3).

FORMAT

TOR

THE

SCRATCH

COMMAND:

SCRATCH

"pattern",Ddrive

#,Uunit

#

32

"pattern"

can be

any

file

nameorcombination

of

characters

and

wild

card

characters.

As

usual,

"D"

stands

for

drive

number,

which

may

onlybe0onthe

1541.Ifthe

drive

numberisomitted,0is

assumed.

Likewise,

"U"

stands

for

unit

(device)

number,

normally

8. If

"U"isomitted,8is

assumed.

Thankstothe

defaults,

the

usual

formofthe

Scratch

command

becomes:

SCRATCH

"pattern"

Asaprecaution,

you

willbeasked:

ARE

YOU

SURE?

■

before

Basic

obeysaScratch

command.Ifyou

are

sure,

Simply

pressYand

RETURN.

If

not,

press

RETURN

aloneortype

any

other

answer,

and

the

command

willbecancelled.

The

numberoffiles

that

were

scratched

willbeautomatically

displayed.

For

exam

ple,ifyour

diskette

contains

program

files

named*'TEST'','

TRAIN",*TRUCK'',

and

"TAIL",

you

may

scratch

all

four,

along

with

any

other

files

beginning

with

the

letter

"T",byusing

the

command:

SCRATCH

"T*"

andifthe

four

listed

were

the

only

files

beginning

with

"T",

you

will

see:

01,FILES

SCRATCHED,04,00

READY.

■

The

"04"

tells

you4files

were

scratched.

SCRATCH

(FOR

ADVANCED

USERS)

Scratchisa

powerful

command,

and

shouldbeused

with

caution,

tobesure

you

only

delete

the

files

you

really

want

erased.

When

usingitwithapattern,wesuggest

you

first

use

the

same

patternina

directory

listing

withanasterisk

(*)

just

before

the

file

type

foranentry.

The

asterisk

(or

splat)

means

that

file

was

never

properly

closed,

and

thus

thereisno

valid

chainofsector

links

for

the

Scratch

commandtofollowinerasing

the

file.

If

you

Scratch

suchafile,

odds

are

you

will

improperly

freeupsectors

that

are

still

neededbyother

programs,

and

cause

permanent

damagetothose

other

programs

later

when

you

add

more

filestothe

diskette.

If

you

findasplat

file,orif

you

discover

too

late

that

you

have

scratched

suchafile,

immediately

validate

the

diskette

using

the

Validate

command

described

laterinthis

chapter.

If

you

have

added

any

filestothe

diskette

since

scratching

the

splat

file,itis

besttoimmediately

copy

the

entire

diskette

onto

another

fresh

diskette,

butdothis

withacopy

.program

rather

than

withabackup

program.

Otherwise,

the

same

problem

willberecreated

on

the

new

diskette.

When

the

new

copy

is

done,

compare

the

numberofblocks

freeinits

directory

to

the

number

freeonthe

original

diskette.

If

the

numbers

match,nodamage

has

been

done.Ifnot,

very

likelyatleast

one

fileonthe

diskette

has

been

corrupted,

and

all

shouldbeimmediately

checked.

Locked

Files

Very

occasionally,

a

diskette

will

contain

a

locked

file;

thatisone

which

cannot

be

erased

with

the

Scratch

command.

Such

files

mayberecognized

by

the

"<"

character

which

immediately

follows

the

file

typeintheir

directory

entry.Ifyou

wishtoerase

a

locked

file,

you

will

havetouseadisk

monitortoclear

bit6of

the

file-type

byteinthe

directory

entryonthe

diskette.

Conversely,

to

lockafile,

you

would

set

bit6of

the

same

byte.

For

more

information

on

how

such

tricks

are

done,

see

Chapter

9 and

Appendices

D

andE.

RENAMING

PROGRAMS:

BASIC

2

The

Rename

command

allows

youtoalter

the

nameofa

programorother

fileinthe

diskette

directory.

Since

only

the directory

is

affected,

Rename

works

very

quickly.

FORMAT

FOR

RENAME

COMMAND:

PRINT#15,"RENAME0:new

name=old

name"

oritmaybeabbreviated

as:

PRINT#15,"R0:new

name=old

name"

where

"new

name"

is

the

name

you

want

the

file

to

have,

and

"old

name"

is

the

name

it

has

now.

"new

name"

may

be

any

valid

file

name,

up

to

16

characters

in

length.

It

is

assumed

you

have

already

opened

file15to

the

command

channel.

One

caution—be

sure

the

file

you

are

renaming

has

been

properly

closed

before

you

rename

it.

34

EXAMPLES:

Just

before

savinganew

copyofa

"calendar"

program,

you

might

type:

PRINT#

15/

'RO:CALENDAR/B

ACKUP=CALENDAR''

Ortomoveaprogram

called

"BOOT",

currently

the

first

programona

diskette

to

someplace

elseinthe

directory,

you

might

type:

PRINT#

15,'

'R0:TEMP=BOOT"

followedbya

Copy

command

(described

later),

which

turns

"TEMP"

intoanew

copy

of

"BOOT",

and

finishing

with

a Scratch

commandtoget

ridofthe

original

copy

of

"BOOT",

since

renamedto"TEMP"bythe

command

above.

RENAMING

PROGRAMS:

BASIC

3.5

The

Rename

command

allows

youtoalter

the

nameofa

programorother

fileinthe

diskette

directory.

Since

only

the

directory

is

affected,

Rename

works

very

quickly.

FORMAT

FOR

RENAME

COMMAND:

RENAME

"old

name"TO"new

name",Ddrive

#,Udevice

#

where

"new

name"isthe

name

you

want

the

filetohave,

and

"old

name"isthe

name

it

has

now.

"new

name"

may

be any

string

expression

that

evaluates

toavalid

file

name,

upto16

characters

in

length.If"D"isleft

out,

drive0is

assumed.If"U"isabsent,

clevice

8isassumed.

One

caution—be

sure

the

file

you

are

renaming

has

been

properly

closed before

you rename

it.

EXAMPLES:

Just

before

savinganew

copyofa

"calendar"

program,

you

might

type:

RENAME

"CALENDAR"TO"CALENDAR/BACKUP"

Ortomoveaprogram

called

"BOOT",

currently

the

first

programona

diskette

to

someplace

elseinthe

directory,

you

might

type:

RENAME

"BOOT"TO"TEMP"

followedbya

Copy

command

(described

later),

which

turns

"TEMP"

intoanew

copy

of

"BOOT",

and

finishing

withaScratch

commandtoget

ridofthe

original

copy

of

"BOOT",

since

renamedto"TEMP"bythe

command

above.

35

RENAMING

AND

SCRATCHING

TROUBLESOME

FILES

(ADVANCED

USERS)

Eventually,

you

may

run

acrossafile

which

hasacrazy

filename,

suchasa

comma

by

itself

(",")orone

that

includes

a

SHIFTed

SPACE.Orperhaps

you

will find

one

that

includes

nonprinting

characters.

Anyofthese

canbetroublesome.

Comma

files,

for

instance,

areanexception

to

the

rule

thatnotwo

files

can

have

the

same

name.

Since

it

shouldn't

be

possibletomakeafile

whose

nameisonlyacomma,

the

disk

never

expects

youtodoitagain.

Files

withaSHIFT-SPACEintheir

name

can

alsobetroublesome,

because

the

disk

interprets

the

shifted

SPACEassignalling

the

endofthe

file

name,

and

prints

whatever

follows

after

the

quotation

mark

that

marks

the

end

of a

nameinthe

directory.

This

technique

can

alsobeuseful,

allowing

youtohavealong

file

name,

but

also

make

the

disk

recognize

a

small

partofitasbeing

the

sameasthe

whole

thing

without

using

pattern-matching

characters.

In

any

case,ifyou

haveatroublesome

filename,

you

can

use

the

Chr$()

function

to

specify

troublesome

characters

without

typing

them

directly.

This

may

allow

youtobuild

them

intoaRename

command.Ifthis

fails,

you

may

also

use

the

pattern-matching

characters

inaScratch

command.

This

gives

youawaytospecify

the

name

without

using

the

troublesome

characters

at

all,

but

also

means

lossofyour

file.

For

example,ifyou

have

managedtocreateafile

named

""MOVIES",

with

an

extra

quotation

markatthe

frontofthe

file

name,

you

can

renameitto

"MOVIES"

by

using

the

Chr$()

equivalent

ofaquotation

markinthe

Rename

command:

BASIC2FORMAT:

PRINT#15,"R0:MOVIES

="+

CHR$(34)+"MOVIES"

BASIC

3.5

FORMAT:

RENAME

(CHR$(34)+"MOVIES")TO"MOVIES"

The

CHR$(34)

forcesaquotation

mark

into

the

command

string

without

upsetting

Basic.

The

procedure

forafile

name

that

includesaSHIFT-SPACEissimilar,

but

uses

CHR$(160).

In

cases

where

even

this

doesn't

work,

for

exampleifyour

diskette

contains

a

comma

file,

(one

named

",")

you

can

get

ridofit

this

way:

BASIC2FORMAT:

BASIC

3.5

FORMAT:

PRINT#15,"S0:?"

SCRATCH"?"

Dependingonthe

exact

problem,

you

may

havetobe

very

creative

in

choosing

pattern-

matching

characters

that

will

affect

only

the

desired

file,

and

may

havetorename

other

files

firsttokeep

them

from

being

scratched

too.

36

COPYING

PROGRAMS:

BASIC

2

The

Copy

command

allows

youtomakeaspare

copyofany

programorfileona

diskette.

However,ona

single

drive

like

the

1541,

the

copy

mustbeon

the

same

diskette,

which

meansitmustbegivenadifferent

name

from

the

file

copied.

It's

also

used

to

concatenate

uptofour

sequential

data

files

(combining

thembylinking

onetoanother,

endtoendina

chain).

Files

are

linkedinthe

orderinwhich

they

appearinthe

command.

The

source

files

and

other

filesonthe

diskette

are

not

changed.

Files

mustbeclosed

before

they

are

copied

or

concatenated*.

FORMAT

FOR

THE

COPY

COMMAND

PRINT#15,44COPYdrive

#:new

file=drive

#:old

file"

EXAMPLES:

PRINT#

15,4

4COPY0:B

ACKUP=ORIGINAL''

or

abbreviated

as

PRINT#15,44Cdrive

#:new

file=drive

#:old

file"

PRINT#

15/

4C0:B

ACKUP=ORIGINAL''

where

4<drive#"is

the

drive

number(0on

the

1541,)

t4new

file"isthe

copy,

and

4<old

file"isthe

original.

FORMAT

FOR

THE

CONCATENATE

OPTION

PRINT#15,44Cdrive

#:new

file=drive

#:file

l,drive#:file

2,drive

#:file

3,drive

#:file4"

where

44drive#"is

the

drive

number

for

each

file.

Sinceitis

always0on

the

1541,

the

drive

numberisoften

omitted.

EXAMPLES:

After

renaming

a

file

named

4<BOOT"to44TEMP"inthe

last

section's

example,

we

can

use

the

Copy

commandtomakeaspare

copyofthe

program

elsewhereonthe

diskette,

under

the

original

name:

PRINT#

15,4

4C0:BOOT=TEMP''

After

creating

several

small

sequential

files

that

each

fit

easilyinmemory

along

with

a

programweare

using,wecan

use

the

concatenate

optiontocombine

themina

master

file,

even

if

the

result

is

too

big

to

fit

in

memory.

(Do

be

sure

it

will

fit

in

remaining

space

on

the

diskette—it

willbeas

bigasthe

sumofthe

sizesofthe

filesinit.)

PRINT#15,44C0:A-Z

=

A-G,H-M,N-Z"

37

NOTE:

Dual

drives

make

fuller

useofthis

command,

copying

programs

from

one

diskette

to

anotherina

single

disk

unit.Todo

thatonthe

1541,

refertoAppendixEto

find

the

programs

that

you

need.

COPYING

PROGRAMS:

BASIC

3.5

The

Copy

command

allows

youtomakeaspare

copyofany

programorfileona

diskette.

However,ona

single

drive

like

the

1541,

the

copy

mustbeon

the

same

diskette,

which

meansitmustbegivenadifferent

name

from

the

file

copied.

The

source

file

and

other

filesonthe

diskette

are

not

changed.

Files

niustbeclosed

before

they

are

copied.

Although

the

1541

supportsaConcatenate

option,

Basic

3.5

doesn't

haveaspecial

command

for

it.

The

Basic2syntax

from

the

maybeused

instead.

FORMAT

FOR

THE

COPY

COMMAND

COPY

Ddrive

#,"old

file"toDdrive

#,"new

file",Udevice

#

where

"D"isthe

drive

number

(always0on

the

1541,)

"new

file"isthe

copy,

"old

file"isthe

original,

and

"U"isthe

device

number.Ifomitted,

the

drive

number

defaults

to0and

the

device

number

(unit)to8.

EXAMPLES:

After

renamingafile

named

"BOOT"to"TEMP"inthe

last

section's

example,

we

can

use

the

Copy

commandtomakeaspare

copyofthe

program

elsewhereonthe

diskette,

under

the

original

name:

COPY

"TEMP"TO"BOOT"

To

copyafileona

second

disk

drive,wewould

use:

COPY

"ORIGINAL"TO"BACKUP"

,U9

NOTE:

Dual

drives

make

fuller

useofthis

command,

copying

programs

from

one

diskette

to

anotherina

single

disk

unit.Todo

thatonthe

1541,

refertoAppendixEto

find

the

programs

that

you

need.

VALIDATING

THE

DISKETTE:

BASIC

2

The

Validate

command

recalculates

the

Block

Availability

Map

(BAM)ofthe

current

diskette,

allocating

only

those

sectors

still

being

usedbyvalid,

properly-closed

files

and

programs.

All

other

sectors

(blocks)

are

left

unallocated

and

free

for

re-use,

and

all

improperly-closed

files

are

automatically

Scratched.

However,

this

bare

description

of

its

workings

doesn't

indicate

either

the

powerorthe

dangerofthe

Validate

command.

Its

powerisin

restoring

to

good

health

many

diskettes

whose

directories

or

block

availability

maps

have

become

muddled.

Any

time

the

blocks

usedbythe

filesona

diskette

plus

the

blocks

shownasfree

don't

addupto

the

664

availableona

fresh

diskette,

Validate

is

needed,

with

one

exception

below.

Similarly,

any

timeadiskette

containsanimproperly-

38

closed

file

(splat

file),

indicated

byanasterisk

(*)

nexttoits

file

typeinthe

directory,

that

diskette

needstobe

validated.

In

fact,

but

for

the

one

exception

below,itisagood

idea

to

validate

diskettes

whenever

you

are the

least

bit

concerned

about

their

integrity.

The

exception

is

diskettes

containing

Direct

Access

files,asdescribed

in

Chapter

7.

Most

direct

access

(random)

filesdonot

allocate

their

sectorsina

way

the

Validate

command

can

recognize.

Thus,

using

Validateonsuchadiskette

may

resultinun-

allocating

all

direct

access

files,

with

lossofall

their

contents

when

other

files

are

added.

Unless

specifically

instructed

otherwise,

never

use

Validate

onadiskette

containing

direct

access

files.

(Note:

these

are

not

the

sameasthe

relative

files

described

in

Chapter

6.

Validate

maybeusedonrelative

files

without

difficulty.)

FORMAT

FOR

THE

VALIDATE

COMMAND

PRINT#15,"VALIDATE*)"

or

abbreviated

as

PRINT#15,"V0"

where

"0"isthe

drive

number

(always0on

the

1541.)Asusual,itis

assumed

file15has

been

openedtothe

command

channelonthe

1541.

EXAMPLE:

PRINT#15,"V0'

VALIDATING

THE

DISKETTE:

BASIC

3.5

The

Collect

commandinBasic

3.5isthe

same

as the

Validate

commandinBasic

2.

It

recalculates

the

Block

Availability

Map

(BAM)ofthe

current

diskette,

allocating

only

those

sectors

still

being

usedbyvalid,

properly-closed

files

and

programs.

All

other

sectors

(blocks)

are

left

unallocated

and

free

for

re-use,

and

all

improperly-closed

files

are

automatically

Scratched.

However,

this

bare

description

of

its

workings

doesn't

indicate

either

the

powerorthe

dangerofthe

Collect

command.

Its

powerisin

restoring

to

good

health

many

diskettes

whose

directories

or

block

availability

maps

have

become

muddled.

Any

time

the

blocks

usedbythe

filesona

diskette

plus

the

blocks

shownasfree

don't

add

uptothe

664

available

onafresh

diskette,

Collectisneeded

(with

one

exception

below.)

Similarly,

any

timeadiskette

containsanimproperly-closed

file

(splat

file),

indicated

by

an

asterisk

(*)

nexttoits

file

typeinthe

directory,

that

diskette

needstobe

collected. In

fact,

but

for

the

one

exception

below,itisagood

ideatocollect

diskettes

whenever

you

are

the

least

bit

concerned

about

their

integrity.

Just

note

the

numberofblocks

freeinthe

diskette's

directory

before

and

after

using

Collect,

andifthe

totals

differ,

there

was

indeed

a

problem,

and

the

diskette

should

probablybecopied

ontoafresh

diskette

filebyfile,

using

the

Copy

command

describedinthe

rather

than

usingabackup

commandorprogram..

The

exceptionisdiskettes

containing

Direct

Access

files,asdescribed

in

Chapter

7.

Most

direct

access

(random)

filesdonot

allocate

their

sectorsina

way

Collect

can

recognize.

Thus,

collecting

suchadiskette

may

resultinun-allocating

all

direct

access

39

files,

with

lossofall

their

contents

when

other

files

are

added.

Unless

specifically

instructed

otherwise,

never

collect

a

diskette

containing

direct

access

files.

(Note:

these

are

not

the

sameasthe

relative

files

describedinChapter6.Collect

maybeused

on

relative

files

without

difficulty.)

FORMAT

FOR

THE

COLLECT

COMMAND

COLLECT

Ddrive

#,Udevice

#

where

"D"isthe

drive

number

(always0on

the

1541,)

and

"U"

the

device

number.

As

usual,ifomitted

they

defaulttodrive0and

device8respectively.

EXAMPLE:

COLLECT

DO

INITIALIZING

One

command

that

should

not

oftenbeneededonthe

1541,

butisstillofoccasional

valueisInitialize.

On

the

1541,

and

nearly

all

other

Commodore

drives,

this

function

is

performed

automatically,

whenever

a

new

diskette

is

inserted.

(The

optical'

write-protect

switch

is

used

to

sense

whenadiskette

is

changed.

>'

The

resultofan

Initialize,

whether

forcedbya

command,ordone

automatically

by

the

disk,isa

re-reading

of

the

current

diskette's

BAM

(Block

Availability

Map)

into

a

disk

buffer.

This

information

must,ofcourse,

alwaysbecorrectinorder

for

the

disk

to

store

new

files

properly.

However,

since

the

choreishandled

automatically,

the

only

time

you'd

needtouse

the

commandisif

something

happenedtomake

the

information

in

the

drive

buffers

unreliable.

Even

so,

you

may

use

the

command

for

reassurance,

as often

as

you

like,solongasyou

close

all

your

files

except

for

the

command

channel

first.

FORMAT

FOR

THE

INITIALIZE

COMMAND

EXAMPLE:

PRINT#15,ttINITIALIZEdrive#"PRINT#

15,"INITIALIZE

0"

oritmaybeabbreviated

to

PKINT#15,''Idrive

#"

PRINT#15,t<I0"

where

the

command

channelisassumedtobe

opened by

file

15,

and

"drive#"is0on

the

1541.

40

One

use

for

Initialize

istokeepacleaning

diskette

spinning,

if

you

choosetouse

one.

(There

is

no

need

to

use

such

kits

on

any

regular

basis

under

normal

conditions

of

cleanliness

and

care.)

Nonetheless,

if

you

are

using

suchakit,

the

following

short

program

will

keep

the

diskette

spinning

long

enough

for

your

need:

10

OPEN

15,8,15

20

FOR

1=1TO99

30:PRINT#15,"I0"

40

CLOSE

15

It

usesanInitialize

looptokeep

the

drive

motoronfor

about20seconds.

41

CHAPTER

5

SEQUENTIAL

DATA

FILES

THE

CONCEPTOFFILES

A

fileona

diskette

is

just

likeafile

cabinetinyour

office—an

organized

placetoput

things.

Nearly

everything

you

putona

diskette

goesinone

kindoffileoranother.Sofar

all

we've

used

are

program

files,

but

there

are

others,aswe

have

mentioned.

In

this

chapterwewill

learn

about

sequential

data

files.

Aswejust

suggested,

the

primary

purposeofa

data

fileisto

store

the

contents

of

program

variables,

so

they

won'tbelost

when

the

program

ends.Asequential

data

file

is

oneinwhich

the

contentsofthe

variables

are

stored

"in

sequence,"

one

right

after

another,

justaseach

linkina

chain

follows

the

You

may

alreadybefamiliar

with

sequential

files

from

usingaDATASSETTE™,

because

sequential

filesondiskette

are

just

like

the

data

files

usedoncassettes.

Whetheroncassette

or

diskette,

sequential

files

mustberead

from

beginning

to

end,

without

skipping

aroundinthe

middle.

When

sequential

files

are created,

information

(data)istransferred

bytebybyte,

throughabuffer,

onto

the

magnetic

media.

Onceinthe

disk

drive,

program

files,

sequential

data

files,

and

user

files

all

work

sequentially.

Even

the

directory

acts

like

a

sequential

file.

To

use

sequential

files

properly,

we

will

learn

some

more

Basic

wordsinthe

pages.

Then

we'll

put

them

together

inasimple

but

useful

program.

Note:

Besides

sequential

data

files,

two

other

file

types

are

recorded

sequentially

onadiskette,

and

maybeconsidered

varying

formsofsequential

files.

They

are

program

files,

and

user

files.

When

you

saveaprogramona

diskette,

itissaved

in

order

from

beginning

to

end,

just

like

the

information

inasequential

data

file.

The

main

difference

isinthe

commands

you

usetoaccess

it.

User

files

are

even

more

similartosequential

data

files—differing,

for

most

purposes,

in

name

only.

User

files

are

almost

never

used,

but

like

program

files,

they

couldbetreatedasthough

they

were

sequential

data

files

and

are

accessed

with

the

same

commands.

For

the

advanced

user,

the

similarity

of

the

various

file

types

offers

the

possibility

of

such

advanced

tricksasreading a

program

file

into

the

computer

a

byte

(character)

atatime

and

rewriting

ittothe

diskette

inamodified

form.

The

ideaofusing

one

programtowrite

anotherispowerful,

and

availableonthe

Commodore

disk

drives.

OPENINGAFILE

Oneofthe

most

powerful

toolsinCommodore

Basicisthe

Open

statement.

With

it,

you

may

send

almost

any

data

almost

anywhere,

much

likeatelephone

switchboard

that

can

connect

any

callertoany

destination.

As

you

might

expect,acommand

that

can

do

this

muchisfairly

complex.

You

have

already

used

Open

statements

regularly

in

some

of

your

diskette

housekeeping

commands.

42

Beforewestudy

the

formatofthe

Open

statement,

let's

review

someofthe

possible

devicesina

Commodore

computer

system:

Device#:Name:

0

1

2

3

4

8

Keyboard

DATASSETTE

RS232

Screen

Printer

Disk

drive

Used

for:

Receiving

input

from

the

computer

operator

Sending

and

receiving

information

from

cassette

Sending

and

receiving

information

fromaModem

Sending

outputtoa

video

display

Sending

outputtoa

hard

copy

printer

Sending

and

receiving

information

from

diskette

Becauseofthe

flexibility

of

the

Open

statement,

itispossible

forasingle

program

statement

to

contact

any

oneofthese

devices,

or

even

others,

dependingonthe

valueofa

single

character

in

the

command.

OftenanOpen

statement

is

the

only

difference

between

a

program

that

usesaDATASSETTE™

and

one

using

the

1541.Ifthe

character

is

kept

in

a

variable,

the

device

used

can

even

change

each

time

that

partofthe

programisused,

sending

data

alternately

and

with

equal

easetodiskette,

cassette,

printer

and

screen.

REMEMBER

TO

CHECK

FOR

DISK

ERRORS!

In

the

last

chapterwelearned

howtocheck

for

disk

errors

after

disk

com

mandsina

program.Itis

equally

important

to

check

for

disk

errors

after

using

file-

handling

statements.

Failuretodetectadisk

error

before

using

another

file-

handling

statement

could

cause

lossofdata,

and

failureofthe

Basic

program.

The

easiest

waytocheck

the

diskisto

follow

all

file-handling

statements

with

a

Gosub

statement

toanerror

check

subroutine.

EXAMPLE:

840

OPEN

4,8,4,"0:DEGREE

DAY

DATA,S,W"

850

GOSUB

59990:REM

CHECK

FOR

DISK

ERRORS

FORMAT

FOR

THE

DISK

OPEN

STATEMENT:

OPEN

file#,device#,channel

#,"drive

#:file

name,file

type,direction"

where:

"file#"isaninteger

(whole

number)

between1and-255.Ifthe

file

number

is

greater

than

127,aline-feed

character

is

inserted

after

each

carriage

returninthe

file

opened.

Though

this

maybehelpfulinprinter

files,

it

will

cause

severe

problemsindisk

files,

andistobeavoidedatall

costs.Donot

openadisk

file

withafile

number

greater

than

127.

After

the

fileisopen,

all

other

file

commands

will

refertoitbythe

number

given

here.

Only

one

file

can

use

any

given

file

numberata

time.

"device#"is

the

number,orprimary

address,ofthe

devicetobe

used.

This

numberisan

integerinthe

range

0-31,

andisnormally8on

the

1541.

43

"channel#"isasecondary

address,

giving

further

instructions

to

the

selected

device

about

how

further

commands

aretobe

obeyed.Indisk

files,

the

channel

number

selects

a

particular

channel

along

which

communications

for

this

file

can

take

place.

The

possible

rangeofdisk

channel

numbersis0-15,

but0is

reserved

for

program

Loads,1for

program

Saves,

and15for the

disk

command

channel.

Also be

sure

thatnotwo

disk

files

have

the

same

channel

number

unless

they

will

neverbeopenatthe

same

time.

(One

way

todothisisto

make

the

channel

number

for

each

file

the

sameasits

file

number.)

"drive#"is

the

drive

number,

always0on

the

1541.Donot

omit

it,oryou

will

onlybeabletouse

two

channels

at

the

same

time

insteadofthe

normal

maximumofthree.

If

any

pre-existing

fileofthe

same

nameistobereplaced,

precede

the

drive

number

with

the

"at"

sign

(@)torequest

Open-with-replace.

"file

name"isthe

file

name,

maximum

length16characters.

Pattern

matching

characters

are

allowedinthe

name

when

accessing

existing

files,

but

not

when

creating

new

ones.

"file

type"isthe

file

type

desired:

S=sequential,

P=program,U=

user,

and

L=lengthofa

relative

file.

"direction"

is

the

typeofaccess

desired.

There

are

three

possibilities:

R=read,

W=write,

andM=

modify.

When

creating

a

file,

use

"W"towrite

the

datatodiskette.

When

viewingacompleted

file,

use

"R"toread

the

data

from

diskette.

Only

use

the

"M"

(modify)

optionasa

last

ditch

wayofreading

back

data

fromanimproperly-closed

(Splat)

file.

(If

you

try

this,

check

every

byteasitisreadtobe

sure

the

dataisstill

valid,

as

such

files

always

include

some

erroneous

data,

and

havenoproper

end.)

"file

type"

and

"direction"

don't

havetobe

abbreviated.

They

canbespelled

out

in

full

for

clarityinprinted

listings.

"file

#",

"device#"and

"channel#"mustbevalid

numeric

constants,

variables

or

expressions.

The

restofthe

command

mustbea

valid

string

literal,

variable

or

expression.

The

maximum

numberoffiles

that

maybeopen

simultaneously

is

10,

including

all

filestoall

devices.

The

maximum

numberofsequential

disk

files

that

canbeopenatonce

is3(or2if

you

neglecttoinclude

the

drive

numberinyour

Open

statement),

plus

the

command

channel.

EXAMPLESOFOPENING

SEQUENTIAL

FILES:

To

createasequential

fileofphone

numbers,

you

could

use:

OPEN2,8,2,"0:PHONES,SEQUENTIAL,WRITE"

or

save

yourself

some

typing

with:

OPEN

2,8,2,"0:PHONES,S,W"

On

the

off-chance

we've

already

gota"PHONES"

fileonour

diskette,

we

can

avoid

a

"FILE

EXISTS"

error

messagebydoingan©OPEN

OPEN

2,8,2,"@0:PHONES,S,W"

44

Of

course,

this

erases

all

our

old

phone

numbers,somake

sure

that

any

information

that

maybedeletedisofnoimportance.

After

writing

our

phone

file,weremove

our

diskette

and

turn

off

the

system.

Later,torecall

the

datainthe

file,wewould

reopenitwith

something

like

OPEN

8,8,8,"0:PHONES,S,R"

It

doesn't

matter

whether

the

file

and

channel

numbers

match

the

onesweused

before,

but

the

file

name

does

havetomatch.

However,itis

possible

to

useanabbreviation

form

of

the

file

name,ifthere

arenoother

files

that

would

have

the

same

abbreviation:

OPEN

10,8,6,"0:PH*,S,R"

Ifwehave

too

many

phone

numbers,

they

might

not

fitinone

file.Inthat

case,

we

might

use

several

similar

file

names,

and

letaprogram

choose

the

correct

file.

100

INPUT

"WHICH

PHONE

FILE

(1-3)";PH

110IFPHO1

AND

PHO2

AND

PH<>3

THEN

100

120

OPEN

4,8,2,"PHONE"

+

STR$(PH)+",S,R"

You

can

omit

the

drive

numberonan

Open

commandtoread a

file.

Doingsoallows

those

with

dual

drivestosearch

both

diskettes

for

the

file.

Note:

Basic2and

Basic

3.5

use

the

same

file

handling

commands

and

the

same

direct

access

commands

(chapters

7-8).

Unless

otherwise

noted,

you

may

use

the

same

commands

for

both

throughout

the

remainderofthis

book.

ADDINGTOA

SEQUENTIAL

FILE

On

Commodore's

PET

and

CBM

models,anAppend

command

allows

youtoreopen

an

existing

sequential

file

and

add

more

information

to

the

endofit.

The

same

thing

can

be

done

another

wayonthe

1541.Inplaceofthe

"type"

and

"direction"

parameters

in

your

Open

statement,

substitute

",A"

for

Append.

This

will

reopen

your

file,

and

position

the

disk

headatthe

endofthe

existing

datainyour

file,

readytoaddtoit.

FORMAT

FOR

THE

APPEND

OPTION

OPEN

file

#,device

#,channel

#,"drive

#:file

name,A"

where,

everything

isason

the

except

for the

ending

"A"

replacing

the

"type"

and

"direction"

parameters.

45

EXAMPLE:

If

you

are

writingagrading

program,itwouldbeconvenient

to

simply

tackoneach

student's

new

gradestothe

endoftheir

existing

grade

files.Toadd

datatothe

"JOHN

PAUL

JONES"

file,wecould

type

OPEN

1,8,3,"0:JOHN

PAUL

JONES,A"

In

this

case,

DOS

will

allocate

at

least

one

more

sector

(block)tothe

file

the

first

time

you

appendtoit,

evenifyou

only

add

one

character

of

information.

You

may

also

notice

that

using

the

CollectorValidate

command

didn't

correct

the

file

size.Onthe

other

hand,

your

dataisquite

safe,

andifthe

wasted

space

becomesaproblem,

you

can

easily

-correct

it

by

copying

the

file

to

the

same

diskette

or a

different

one,

and

scratching

the

original

file.

Here'sasequenceofcommands

that

will

copy

such

filestothe

original

diskette

under

the

original

name,

for

easeofcontinued

use:

BASIC

2:

PRINT#15,"R0:TEMP

=

JOHN

PAUL

JONES"

PRINT#15,<tC0:JOHN

PAUL

JONES=TEMFf

PRINT#15,"S0:TEMP"

BASIC

3.5:

RENAME

"JOHN

PAUL

JONES"TO"TEMP"

COPY

"TEMP"TO"JOHN

PAUL

JONES"

SCRATCH

"TEMP"

If

you

are

using

Basic2,be

suretoopen

file15to

the

command

channel

beforehand

(i.e.,

with

OPEN

15,8,15)

and

closeitafterwards

(i.e.,

with

CLOSE

15).

WRITING

FILE

DATA:

USING

PRINT#

Afterasequential

file

has

been

openedtowrite

(withatype

and

direction

of

",S,W"),weuse

the

Print#

commandtosend

datatoit

for

storageondiskette.

If

you

are

familiar

with

Basic's

Print

statement,

you

will

find

Print#

works

exactly

the

same

way,

except

that

the

listofitems

following

the

command

wordissenttoa

particular

file,

insteadofautomatically

appearingonthe

screen.

Even

the

formatting

options

(punctua

tion

and

such)

workinmuch

the

same

wayasin

Print

statements.

This

means

you

have

to

be

sure

the

items

sent

make

sensetothe

particular

file

and

device

used.

For

instance,

a

comma

between

variables

inaPrint

statement

actsasa

separator

in

screen

displays,

making

each

successive

item

appearinthe

display

field

(typically

at

the

whose

numberisevenly

divisible

by

10).Ifthe

same

comma

is

included

between

variables

goingtoa disk

file,itwill

again

actasa

separator,

again

inserting

extra

spaces

into

the

data.

This

time,

however,itis

inappropriate,

as

the

extra

spaces

are

simply

wastedonthe

diskette,

and

may

create

more

problems

when

reading

the

file

back

into

the

computer.

Therefore,

you

are

urgedtofollow

the

following

format

precisely

when

sending

datatoa

disk

file.

FORMAT

FOR

THE

PRINT#STATEMENT

PRINT#file#,data

list

46

where

"file#"is

the

same

file

number

giveninthe

desired

file's

current

Open

statement.

During

any

given

accessofa

particular

file,

the

file

number

must

remain

constant

because

it

servesasa

shorthand

wayofrelating

all

other

file-handling

commands

backtothe

correct

Open

statement.

Givenafile

number,

the

computer

can

lookupeverything

else

aboutafile

that

matters.

The

"data

list"isthe

sameasforaPrint

statement

-alistofconstants,

variables

and/or

expressions,

including

numbers,

stringsorboth.

However,itis

strongly

recom

mended

that

each

Print#

statement

to

disk

include

only

one

data

item.Ifyou

wish

to

include

more

items,

they

mustbeseparated

byacarriage

return

character,

notacomma.

Semicolons

are

permitted,

but

not

recordedinthe

file,

anddonot

resultinany

added

spacesinthe

file.

Use

themtoseparate

itemsinthe

list

that

might

otherwisebeconfused,

suchasa

string

variable

immediately

following

a

numeric

variable.

Note:Donot

leaveaspace

between

PRINT

and#,anddonot

abbreviate

the

commandas?#.

The

correct

abbreviation

for

Print#ispR.

EXAMPLES:

To

recordafew

grades

for

John

Paul

Jones,

usingasequential

disk

file#1previously

opened

for writing,wecould

use:

200

FOR

CLASS=1TOCOURSES

210:

PRINT#1,GRADE$(CLASS)

220

320

GOSUB

59990:REM

CHECK

FOR

DISK

ERRORS

(assuming

your

program

includesanerror

check

subroutine

like

the

oneinthe

last

chapter).

In

using

Print#

there

is

an

exception

to

the

requirement

to

check

for

disk

errors

after

every

file-handling

statement.

When

using

Print#,asingle

check

after

an

entire

set

of

data

has

been

written

will

still

detect

the

error,

so

long

as

the

check

is

made

before

any

other

file-handling

statement

or

disk

command

is

used.

You

may

be

familiar

with

Print

statements

in

which

several

items

follow

each

other:

400

PRINT

NAME$,STREET$,CITY$

To

get

those

same

variables

onto

sequential

disk

file

number5instead

of

the

screen,

the

best

approach

wouldbeto

use

three

separate

Print#

statements,

as

follows:

400

PRINT#5,NAME$

410PRBSfT#5,STREET$

420PRINT#5,CITY$

47

However,ifyou

needtocombine

them,

hereisa

safe

waytodo

it:

400PRINT#5,NAME$;CHR$(13);STREET$;CHR$(13);CITY$

CHR$(13)isthe

carriage

return

character,

and

has

the

same

effectasputting

the

print

itemsinseparate

lines.Ifyoudothis

often,

some

space

and

time

maybesaved

by

previously

defining

a

variableasequaltoCHR$(13):

10CR$=CHR$(13)...

400PRINT#5,NAME$;CR$;STREET$;CR$;CITY$

The

basic

ideaisthataproper

sequential

disk

file

write,ifredirected

to

the

screen,

will

display

only

one

data

item

per

line,

with

each

succeeding

itemonthe

CLOSINGAFILE

WHEN

YOU

ARE

DONE

USING

IT

After

you

finish

usingadata

file,itis

extremely

important

that

you

Close

it.

During

the

processofwritingafile,

dataisaccumulated

inamemory

buffer,

and

only

written

out

to

the

physical

cassette

or

diskette

when

the

buffer

fills.

Working

this

way,

thereisalmost

alwaysasmall

amountofdatainthe

buffer

that

has

not

been

writtentodisketteorcassette

yet,

and

which

would

simplybelostifthe

computer

system

were

turned

off.

Similarly,

there

are

diskette

housekeeping

matters,

such

as

updating

the

BAM

(Block

Availability

Map)ofsectors

usedbythe

current

file,

which

are

not

performed

during

the

ordinary

courseofwritingafile.

Thisisthe

reason

for

havingaClose

statement.

Whenweknow we

are

done

withafile,

the

Close

statement

will

write the

restofthe

data

buffer

outtocassetteordiskette,

update

the

BAM,

and

complete

the

file's

entryinthe

directory.

Always

Closeadata

file

when

you

are

done

using

it!

Failuretodosomay

cause

lossofthe

entire

file!

However, do

not

cloSe

the

disk

command

channel

until

all

other

files

have

been

Closed.

The

command

channel

(described

in

the

last

chapter),

when

used,

shouldbethe

first

file

Opened,

and

the

last

file

Closedinany

program.

Otherwise,

remaining

files

may

be

closed

automatically.

As

also

described

there,

this

may

be usedtoadvantageifa

program

haltsonan

error

while

disk

files

are

open.

FORMAT

FOR

THE

CLOSE

STATEMENT

CLOSE

file

#

where

"file#"is

the

same

file

number

giveninthe

desired

file's

current

Open

statement.

EXAMPLES:

To

close

the

data

file#5usedasan

exampleonthe

use

CLOSE

5

In

Commodore's

CBM

and

PET

computers,

thereisa

Dclose

statement,

that,

when

used

alone,

closes

all

disk

filesatonce.

Withabitofplanning,

the

same

canbedone

in

Basic2and

3.5

viaaprogram

loop.

Since

thereisno

harminclosingafile

that

wasn't

48

open,

close

every

file

you

even

think

might

be

open

before

endingaprogram.

If

for

example,wealways

gave

our

files

numbers

between1and

10,wecould

close

them

all

with

9950FORI=lTO10

9960

CLOSE

I

9970

GOSUB

59990:REM

CHECK

FOR

DISK

ERRORS

9980

(assuming

your

program

includes

an

error

check

subroutine

like

the

oneinChapter

4)

READING

FILE

DATA: USING

INPUT#

Once

information

has

been

written

properly

toadiskette

file,itmayberead

back

into

the

computer

withanInput#

statement.

Justasthe

Print#

statement

is

much

like

the

Print

statement,

Input#

is

nearly

identical

to

Input,

except

that

the

list

of

items

following

the

command

word

comes

fromaparticular

file

insteadofthe

keyboard.

Both

statements

are

subject

to"the

same

limitations—halting

input

afteracomma

or colon,

not

accepting

data

items

too

largetofitinBasic's

Input

buffer,

and

not

accepting

non-numeric

data

into

a

numeric

variable.

FORMAT

FOR

THE

INPUT#

STATEMENT

PRINT#file

#,variable

list

where

"file#"is

the

same

file

number

giveninthe

desired

file's

current

Open

statement,

and

"variable

list"isoneormore

valid

Basic

variable

names.Ifmore

than

one

data

elementistobeinputbya

particular

Input#

statement,

each

variable

name

must

be

separated

from

othersbya

comma.

EXAMPLES:

To

read

backinthe

grades

written

with

the

Print#

example,

use:

300

FOR

CLASS=1TOCOURSES

310

INPUT#1,GRADE$(CLASS)

320

GOSUB

59990:REM

CHECK

FOR

DISK

ERRORS

330

(assuming

your

program

includes

an

error

check

subroutine

like

the

one

on

page

27).

To

read

back

in

the

address data

written

by

another

Print#

example,

it

is

safest

to

use:

800INPUT#5,NAME$

810

GOSUB

59990:REM

CHECK

FOR

DISK

ERRORS

820

INPUT#5,STREET$

830

GOSUB

59990.REM

CHECK

FOR

DISK

ERRORS

840INPUT#5,CITY$

850

GOSUB

59990:REM

CHECK

FOR

DISK

ERRORS

49

but

many

programs

cheatonsafetyabit

ana

use

800

INPUT#5,NAME$,STREET$,CITY$

810

GOSUB

59990:REM

CHECK

FOR

DISK

ERRORS

Thisisdone

primarily

when

top

speedinthe

programisessential,

and

thereislittleorno

riskofreading

improper

data

from

the

file.

MORE

ABOUT

INPUT#

(FOR

ADVANCED

USERS)

Troublesome

Characters

After

you

begin

using

data

files

regularly,

you

may

encounter

two

Basic

error

messages

moreorless

frequently.

They

are

"STRING

TOO

LONG

ERROR"

and

"FILE

DATA

ERROR".

Both

are

likelytohalt

your

programatan

Input#

statement,

but

may

also

have

been

causedbyerrorsina

Print#

statement

when

the

file

was

written.

"STRING

TOO

LONG"

ERRORS

A

Basic

string

maybeupto255

characters

long,

although

the

longest

string

you

can

enter

viaasingle

Input

statement

is

just

under2linesoftext(4on

the

VIC

20).

This

lower

limitation

is

duetothe88character

sizeofthe

Input

bufferinCommodore's

serial

bus

computers.

The

same

limit

appliestoInput#

statements.

Ifasingle

data

element

(string

or

number)

being

read

fromadisk

file

intoanInput#

statement

contains

more

than

87

characters,

Basic

will

halt

witha"STRING

TOO

LONG

ERROR".Toprevent

this

error,besuretolimit

each

stringtounder88characters,

and

separate

all

file

data

items

with

carriage

returns

(See

the

foracure

once

the

error

has

occurred.)

"FILE

DATA"

ERRORS

The

other

error

message

"FILE

DATA

ERROR"iscausedbyattempting

to

read

a

non-numeric

character

intoanumeric

variable.

Toacomputer,

a

numberisthe

characters

0

through

9,

the"+"an3"-"signs,

the

decimal

point

(.),

the

SPACE

character,

and

the

letter

"E"

usedinscientific

notation.

If

any

other

character

appearsinan

Input#toa

numeric

variable,

"FILE

DATA

ERROR"

willbedisplayed

and

the

program

will

halt.

The

usual

causesofthis

error

areamismatch

between

the

orderinwhich

variables

are

writtentoand

read

fromafile,amissing

carriage

return

withinaPrint#

statement

that

writes

more

than

one

data

item,ora

data

item

that

includes

eitheracommaora colon

withoutapreceding

quotation

mark.

Onceafile

data

error

has

occurred,

you

should

correctitby

reading

the

data

item

intoastring

variable,

and

then

converting

it

backtoa

number

with

the

Basic

Val()

statement

after

removing

non-numeric

characters

with

the

string

functions

described

in

your

computer

users

manual.

COMMAS

(,)

AND

COLONS

(:)

As

suggested

before,

commas

and

colons

can

cause

troubleina

file,

because

they

delimit

(end)

the

data

elementinwhich

they

appear

and

cause

any

remaining

characters

in

the

data

elementtobe

read

into

the

variable.

(They

have

the

same

effectinan

Input

statement,

causing

the

common

"EXTRA

IGNORED"

error

message.)

However,

sometimeswereally

needacommaorcolon

withinadata

element,

suchasa

name

written

as

"Last,

First".

The

cureisto

precede

such

data

elements

withaquotation

mark.

After

a

50

quotation

mark,ineitheranInputorInput#

statement,

all

other

characters

except

a

carriage

returnoranother

quotation

mark

are

acceptedaspartofthe

current

data

element.

EXAMPLES:

To

forceaquotation

mark

intoadata

element

goingtoa

file,

appendaCHR$(34)

to

"

the

start

of

the

data

element.

For

example:

PRINT#2,CHR$(34)

-I-''STRASMA,

JIM''

or

PRINT#2,CHR$(34);4<STRASMA,

JIM"

If

youdothis

often,

some

space

and

time

maybesavedbypreviously

defining

a

variable

as

equaltoCHR$(34)aswe

did

earlier

with

CHR$(13):

20QT$=CHR$(34)

400

PRINT#5,QT$+NAMES

In

each

case,

the

added

quotation

mark

willbestripped

outofthe

databythe

Input

or

Input#

statement,

but

the

commaorcolon

will

remain

safely

partofthe

data.

NUMERIC

DATA

STORAGEONDISKETTE

Inside

the

computer,

the

space

occupiedbya

numeric

variable

depends

onlyonits

type.

Simple

numeric

variables

use7bytes

(character

locations)

of

memory.

Real

array

variables

use5bytes

per

array

element,

and

integer

array

elements

use2bytes-

each.

In

contrast,

whenanumeric

variableorany

typeiswrittentoa

file,

the

spaceitoccupies

depends

entirely

on

its

length,

not

its

type.

Numeric

dataiswrittentoa

fileinthe

formofa

string,asif

the

Str$()

function

had

been

performedonit.

The

first

character

willbea

blank

spaceifthe

numberispositive,

andaminus

sign

(-)ifthe

numberisnegative.

Then

comes

the

number,

digitbydigit.

The

last

character

isacursor

right

character.

This

format

allows

the

disk

datatobe

read

back

intoastringornumeric

variable

later.

It

is,

however,

somewhat

wasteful

of

disk

space,

and

it

can

be

difficult

to

anticipate

the

space

requiredbynumbersofunknown

length.

For

this

reason,

some

programs

convert

all

numeric

variables

into

strings

before

writing

themtodiskette,

and

use

string

functions

to

remove

any

unneeded

characters

in

advance.

Doingsostill

allows

those

data

elements

toberead

back

intoanumeric

variable

by

Input#

later,

although

file

data

errors

maybeavoidedbyreading

all

datainas

strings,

and

converting

to

numbers

after

the

information

is

inside

the

computer.

For

example,

t4N$=MID$(STR$(N),2)"

will

convertapositive

numberNinto

a

stringN$without

the

usual

leading

space

for

its

numeric

sign.

Then

insteadofwriting

PRINT#5,N,

you

would

use

PRINT#5,N$.

51

READING

FILE

DATA:

USING

GET#

The

Get#

statement

retrieves

data

from

the

disk

drive,

one

character

atatime.

Like

the

similar

keyboard

Get

statement

in

Basic,itonly

acceptsasingle

character

into

a

specified

variable.

However,

unlike

the

Get

statement,

it

doesn't

just

fall

throughtothe

if

thereisno

datatobe

gotten.

The

primary

useofGet#isto retrieve

from

diskette

any

data

that

cannotberead

intoanInput#

statement,

either

becauseitis

too

long

to

fitinthe

input

bufferorbecauseitincludes

troublesome

characters.

FORMAT

FOR

THE

GET#

STATEMENT:

GET#file#,variable

list

where

"file#"is

the

same

file

number

giveninthe

desired

file's

current

Open

statement,

and

"variable

list"isoneormore

valid

Basic

variable

names.Ifmore

than

one

data

elementistobeinputbya

particular

Get#

statement,

each

variable

name

must

be

separated

from

othersbya

comma.

In

practice,

you

will

almost

never

seeaGetorGet#

statement

containing

more

than

one

variable

name.Ifmore

than

one

character

is

needed,

a loopisused

rather

than

additional

variables.

Alsoasin

the

Input#

statement,

itissafertouse

string

variables

when

the

filetobe

read

might

containanon-numeric

character.

Dataina

Get#

statement

comesinbytebybyte,

including

such

normally

invisible

characters

as

the

Carriage

Return,

and

the

various

cursor

controls.

All

but

one

willberead

properly.

The

exceptionisCHR$(0),

the

ASCII

Null

character.

Itisdifferent

from

an

empty

string

(oneofthe

formA$=""),

even

though

empty

strings

are

often

referred

to

as

null

strings.

Unfortunately,

inaGet#

statement,

CHR$(0)isconverted

intoanempty

string.

The

cureisto

test

foranempty

string

afteraGet#,

and

replace

any

that

are

found

with

CHR$(0)

instead.

The

first

example

below

illustrates

the

method.

EXAMPLES:

To

readafile

that

may

containaCHR$(0),

suchasa

machine

language

program

file,

we

could

correct

any

CHR$(0)

bytes

with

1100

GET#3,G$:IF

G$ =""THENG$=

CHR$(0)

Ifanoverlong

string

has

managedtobe

recordedina

file,itmaybesafely

read

back

into

the

computer

with

Get#,

usingaloop

suchasthis

3300B$=

""

3310GET#l,A$

3320IFA$<>CHR$(13)

THENB$=B$+

A$:GOTO

3310

The

limit

for

suchatechnique

is

255

characters.

It

will

ignore

CHR$(0),

but

that

may

be

an

advantageinbuilding

a

text

string.

52

Get#

maybeespecially

usefulinrecovering

damaged

files,orfiles

with

unknown

contents.

The

Basic

reserved

variableST(the

file

STatus

variable)

canbeusedtoindicate

when

allofa

properly-closed

file

has

been

read.

500

GET#2,S$

510SU=

ST:REM

REMEMBER

FILE

STATUS

520

PRINT

S$;

530IFSU=0

THEN

500:REMIFTHERE'S

MORETOBE

REAL

540IFSUO64

THEN

PRINT

"STATUS

ERROR:ST=

";SU

CopyingSTintoSUis

often

an unneccessary

precaution,

but

mustbedoneifany

other

file-handling

statement

appears

between

the

one

which

read

from

the

file

and

the

one

that

loops

backtoread

again.

For

example,itwouldberequired

if

line

520

was

changed

to

520PRINT#l,S$;

Otherwise,

the

file

status

checkedinline

530

wouldbethatofthe

write

file,

not

the

read

file.

POSSIBLE

VALUESOFTHE

FILE

STATUS

VARIABLE

t4ST",

IFST

=

0

1

2

4

8

16

32

64

128

AND

THEIR

MEANINGS

THEN

AllisOK

Receiving

device

was

not

available

(time

outontalker)

Transmitting

device

was

not

available

(time

outonlistener)

Cassette

data

file

block

was

too

short

Cassette

data

file

block

was

too

long

Unrecoverable

read

error

from

cassette,

verify

error

Cassette

checksum

error—oneormore

faulty

characters

were

read

Endoffile

reached

(EOI

detected)

Device

not

present,orendoftape

mark

foundoncassette

53

DEMONSTRATIONOFSEQUENTIAL

FILES

Use

the

following

program

for

your

Comments

have

been

addedtohelp

you

150CR$=CHR$(13)

160

OPEN

15,8,15

170

PRINT

CHR$(147):REM

CLEAR

SCREEN

190

PRINT

"**

WRITEAFILE

**"

210

PRINT

220

OPEN

2,8,2,"@0:SEQ

FILE,S,W"

230

GOSUB

500

240

PRINT'ENTER

A WORD,

THENANUMBER1*

250

PRINT"OR

4END,0'TOSTOP*'

260

PRINT

270

INPUT

A$,B

280

PRINT#2,A$;CR$;B

290

GOSUB

500

300IFA$O"END"

THEN

270

310

PRINT

320

CLOSE

2

340

PRINT

"**

READ

SAME

FILE

BACK

**"

360

PRINT

370

OPEN

2,8,2,"0:SEQ

FILE,S,R"

380

GOSUB

500

390

INPUT#2,A$,B

400RS=ST

410

GOSUB

500

420

PRINT

A$,B

430IFRS=0

THEN

390

440IFRSO64

THEN

PRINTt4STATUS=";RS

450

CLOSE

2

460

END

480

REM**ERROR

CHECK

S/R

**

500

INPUT#15,EN,EM$,ET,ES

510IFEN>0

THEN

PRINT

EN,EM$,ET,ES:STOP

520

RETURN

first

experiments

with

sequential

files.

better

understand

it.

Makeacarriage

return

variable

Open

demo

file

with

replace

Check

for

disk

errors

Acceptastring&number

from

keyboard

Write

themtothe

disk

file

Until

finished

Tidy

up

Reopen

same

file

for

reading

Read

from

file

Remember

file

status

Display

file

contents

until

done,

unless

there'sanerror

Then

quit

A

Basic

3.5-only

version

could

replace

line

500

with

500IFDS>0

THEN

PRINT

DS$:STOP

and

delete

line

510

54

CHAPTER

6

RELATIVE

DATA

FILES

THE

VALUE

OF

RELATIVE

ACCESS

Sequential

files

are

very

useful

when

you're

just

working

with

a continuous

stream

of

data—

i.e.,

information

that

canbereadorwritten

allatonce.

However,

sequential

files

are

not

usefulordesirable

in

some

situations.

For

example,

after

writingalarge

list

of

mail

labels,

you

wouldn't

wanttohavetore-read

the

entire

list

each

time

you

need

a

person's

record.

Instead,

you

need

some

kindofrandom

access,awaytogettoa

particular

labelinyour

file

without

havingtoread

through

all

those

preceding

it

first.

Asanexample,

comparearecord

turntable

withacassette

recorder.

You

have

to

listentoa

cassette

from

beginningtoend,

butaturntable

needle

canbepickedupat

any

time,

and

instantly

movedtoany

spotonthe

record.

Your

disk

drive

works

likeaturntable

in

that

respect.

In

this

chapterwewill

learn

aboutatypeoffile

that

reflects

this

flexibility.

Actually,

two

different

typesofrandom

access

files

maybeusedonCommodore

disk

drives:

relative

files

and

random

files.

Relative

files

are

much

more

convenient

for

most

data

handling

operations,

but

true

random

access

file

commands

are

also

available

to

advanced

users,

and

willbediscussedinthe

FILES,

RECORDS,

AND

FIELDS

When

learning

about

sequential

files,wedid

not

worry

about

the

organization

of

data

withinafile,solongasthe

variables

usedtowrite

the

file

matchedupproperly

with

those

which

readitback

into

the

computer.

Butinorder

for

relative

accesstowork,weneed

a

more

structured

and

predictable

environment

for

our

data.

The

structurewewill

useissimilartothat

usedinthe

traditional

filing

cabinet.Ina

traditional

office,

all

customer

records

mightbekeptina

single

file

cabinet.

Within

this

file,

each

customer

has a

personal

recordina

file

folder

with

their

nameonit,

that

contains

everything

the

office

knows

about

that

person.

Likewise,

within

each

file

folder,

there

maybemany

small

slipsofpaper,

each

containing

one

bitofinformation

about

that

customer,

suchasa

home

phone

number,orthe

dateofthe

most

recent

purchase.

Inacomputerized

office,

the

file

cabinetisgone,

but

the

conceptofa

file

containing

all

the

information

aboutagrouportopic

remains.

The

file

folders are

gone

too,

but

the

notionofsubdividing

the

file

into

individual

records

remains.

The

slipsofpaper

within

the

personal

records

are

gone

too,

replacedbysubdivisions

within

the

records,

called

fields.

Each

fieldislarge

enoughtohold

one

pieceofinformation

about

one

recordinthe

file.

Thus,

within

each

file

there

are

many

records,

and

within

each

record

there

are

typically

many

fields.

A

relative

file

takes

careoforganizing

the

records

for

you,

numbering

them

from1to

whatever,byones,

but

the

fields

areupto

youtoorganize.

Each

record

willbeof

the

same

size,

but

the

1541

won't

insist

that

they

allbedivided

the

same

way.Onthe

other

hand,

they

normally

will

allbesubdivided

the

same

way,

andifit

canbeknown

in

advance

exactly

where

each

field

starts

within

each

record,

there

are

even

fast

ways

to

accessadesired

field

withinarecord

without

reading

through

the

other

fields.Asall

of

this

implies,

access

speedisa

primary

reason

for

putting

information

intoarelative

disk

file.

Some

well-written

relative

file

programs

are

abletofind

and

read

the

recordofone

'55

desired

person

outofa

thousandinunder15seconds,

a

featnosequential

file

program

could

match.

FILE

LIMITS

Oneofthe

nicest

aspectsofrelative

filesisthat

all

thisisdone

for

you

without

your

havingtoworryatall

about

exactly

whereonthe

diskette's

surface

a

given

record

will

be

stored,

or

whetheritwill

fit

properly

within

the^current

disk

sector,

or

needtobe

extended

onto

the

sector.

DOS

takes

careofall

that

for

you.

All

you

needtodo

is

specify

how

long

each

record

is,inbytes,

and

how

many

records

you

will

need.

DOS

will

do

the

rest,

and

organize

thingsinsuchaway

thatitcan

quickly

find

any

recordinthe

file,

as

soonasitisgiven

its

record

number

(ordinal

position

within

the

file).

The

only

limit

that

will

concern

you,isthat

each

record

mustbethe

same

size,

and

the

record

length

you

choose

mustbebetween2and

254

characters.

Naturally

the

entire

file

also

has

to

fit

on

your

diskette

too,

which

means

that

the

more

records

you

need,

the

shorter

each

must

be.

CREATINGARELATIVE

FILE

Whenarelative

fileistobeused

for

the

first

time,

its

Open

statement

will

create

the

file;

after

that,

the

same

Open

statement

will

be usedtoreopen

the

file

for

both

reading

and

writing.

FORMAT

STATEMENTTOOPENARELATIVE

FILE:

OPEN

file#,device#,channel#,"drive#:file

name,

L,"+CHR$

(record

length)

where

"file#"is

the

file

number,

normallyaninteger

between1and

127;

"device#"is

the

device

number

to

be

used,

normally

8

on

the

1541;

"channel

#"

selects

a

particular

channel

along

which

communications

for

this

file

can

take

place,

normally

between2and

14;

"drive#"is

the

drive

number,

always0on

the

1541;

and

"file

name'*isthe

file

name,

with a

maximum

lengthof16

characters.

Pattern

matching

characters

are

allowed

in

the

name

when

accessing

an

existing

file,

but

not

when

creating

a

new

one.

The

"record

length"isthe

sizeofeach

record

within

the

fileinbytes

used,

including

carriage

returns,

quotation

marks

and

other

special

characters.

56

Notes:

1.Donot

precede

the

drive

number

with

the

"at"

sign

(@);

thereisno

reason

to

replacearelative

file.

2.,L,"+CHR$(record

length)isonly

required

whenarelative

fileisfirst

created,

thoughitmay

used

later,solongasthe

"record

length"isthe

same

as

when

the

file

was

first

created.

Since

relative

files

mayberead

fromorwritten

to

alternately

and

with

equal

ease, thereisno

needtospecify

ReadorWrite

mode

when

openingarelative

file.

3.

"file

#",

"device#"and

"channel#"mustbevalid

numeric

constants,

variables

or

expressions.

The

restofthe

command

mustbea

valid

string

literal,

variableorexpression.

4.

Only1relative

file

canbeopenata

timeonthe

1541,

although

a

sequential

file

and

the

command

channel

may

alsobeopenatthe

same

time.

EXAMPLES:

To

createorre-open

a

relative

file

named

"GRADES",ofrecord

length

100,

use

OPEN

2,8,2,"GRADES,L,"

+CHR$(100)

To

re-openanunknown

relative

fileofthe

user's

choice

that

has

already

been

created,wecould

use

200

INPUT"WHICH

FILE";FI$

210

OPEN

5,8,5,FI$

USING

RELATIVE

FILES:

RECORD#

Whenarelative

fileisopened

for

the

first

time,itis

not

quite

ready

for

use.

Both

to

save

time

when

using

the

file

later,

andtoassure

that

the

file

will

work

reliably,

it

is

necessary

to

create

several

records

before

closing

the

file

for the

first

time.Ata

minimum,

enough

recordstofill

more

than2disk

sectors

(512

bytes)

shouldbewritten.

In

practice,

most

programsgoahead

and

createasmany

recordsasthe

programiseventually

expected

to

use.

That

approach

has

the

additional

benefitofavoiding

such

problemsasrunning

out

of

roomonthe

diskette

before

the

entire

fileiscompleted.

If

you

simply

begin

writing

datatoa

just-opened

relative

file,itwill

act

much

like

a

sequential

file,

putting

the

data

elements

writtenbythe

first

Print#

statement

in

Record

#1,

those

writtenbythe

second

Print#

statement

in

record#2andsoon.

(As

this

implies,

each

relative

record

mustbewrittenbya

single

Print#

statement,

using

embed

ded

carriage

returns

within

the

datatoseparate

fields

that

willbereadinvia

oneormore

Input#

statements

later.)

However,itis

far

better to

explicitly

specify

which

record

numberisdesired

viaaRecord#

commandtothe

disk.

This

allows

youtoaccess

records

in

any

desired

order,

hopping

anywhereina

file

with

equal

ease.

Properly

used,italso

avoidsasubtle

error

(bug)

commontoall

Commodore

disk

drives.

57

FORMAT

FOR

THE

RECORD#

COMMAND:

PRINT#15,

"Pff+CHR$

(channel

#+96)+CHR$

(<record#)+

CHR$

(>record#)+

CHR$

(offset)

where

"channel#"is

the

channel

number

specified

in

the

current

Open

statement

for

the

specified

file,

"<record#"is

the

low

byteofthe

desired

record

number,

expressed

as

a

two

byte

integer,

">record#"is

the

high

byteofthe

desired

record

number,

and

an

optional

"offset"

vaiue,

if

present,

is

the

byte

within

the

record

at

whichafollowing

ReadorWrite

should

begin.

To

fully

understand

this

command,wemust

understand

how

most

integers

are stored

in

computers

basedonthe

6502

and

In

the

binary

arithmetic

used

by

the

microprocessor,

itispossibletoexpress

any

unsigned

integer

from

0-255ina

single

byte.Itis

also

possible

to

store

any

unsigned

integer

from

0-65535in2

bytes,

with

1

byte

holding

the

partofthe

number

thatisevenly

divisible

by

256,

and any

remainder

in

the

other

byte.Inmachine

language,

such

numbers

are

written

backwards,

with

the

low-

order

byte

(the

remainder)

first,

followedbythe

high

order

byte.Inassemhly

language

programs

written

with

the

Commodore

Assembler,

the

low

partofa

two

byte

number

is

indicated

by

preceding

its

label

with

the

less-than

character

(<).

Similarly,

the

high

part

of

the

numberisindicated

by

greater-than

(>).

SAFETY

NOTE:

GIVE

EACH

RECORD#

COMMAND

TWICE!

To

avoid

the

remote

possibility

of

corrupting

relative

file

data,itis

necessary

to

give

Record#

commands

twice—once

beforearecordisread or

written,

and

again

immediately

afterwards.

EXAMPLES:

To

position

the

record

pointer

for

file

number2to

record

number3,we

could

type:

PRINT

#15,

"P"+CHR$

(98)+CHR$

(3)+CHR$

(0)

The

CHR$(98)

comes

from

adding

the

constant

(96)

to

the

desired

channel

number

(2).

(96+2=98)

Although

the

command

appears

to

work

even

when

96

is

not

added

to

the

channel

number,

the

constant

is

noimally

added

to

maintain

compatibility

with

the

way

Record#

works

on

Commodore's

CBM

and

PET

computers.

Since3is

less

than

256,

the

high

byte

of

its

binary

representation

is

0,

and

the

entire

value

fits

into

the

low

byte.

Since

we

want

to

read

or

write

from

the

beginning

of

the

record,nooffset

valueisneeded.

Since

these

calculations

quickly

become

tedious,

most

programs

urc

written

to

do

them

for

you.

Here

is

an

example

ofaprogram

which

inputs

a

record

number

and

converts

it

into

the

required

low

byte/high

byte

form:

58

450

INPUT"RECORD#DESIRED";RE

46aIFRE<1ORRE>65535

THEN

450

470RH=INT(RE/256)

480RL =

RE-256*RH

490

PRINT#15,

"P"

+CHR$

(98)

+CHR$

(RL)+CHR$

(RH)

Assuming

RH

andRLare

calculated

asinthe

programs

may

also

use

variables

for

the

channel,

record,

and

offset

required:

570

INPUT

"CHANNEL,

RECORD,&OFFSET

DESIRED";CH,RE,OF

630

PRINT#15,"P"+CHR$(CH+96)+CHR$(RL)+CHR$(RH)+CHR$

(OF)

ANOTHER

RECORD#

COMMAND

Basic

4.0onCommodore's

PET

and

CBM

models

includes

a

Basic

Record#

command

not

foundinanyofthe

serial

bus

computers.

However,

some

available

utility

programs

for

these

models

include

it.Itserves

the

same

functionasthe

Record#

command

explained

above,

but

hasasimplified

syntax:

RECORD#file

#,record

#,offset

where

"file#"is

the

relative

file

number

being

used,

not

the

command

channel's

file,

"record#"is

the

desired

record

number,

and

"offset"isas

above.

If

you

seeaRecord#

command

writteninBasic4formina

program

you

want

to

use,

simply

convertitinto

the

usual

form

for

both

Basic2and

3.5

described

in

this

section.

COMPLETING

RELATIVE

FILE

CREATION

Now

thatwehave

learned

howtouse

both

the

Open

and

Record#

commands,weare

almost

readytoproperly

createarelative

file.

The

only

additional

factweneedtoknow

is

that

CHR$(255)isa

special

character

inarelative

file.Itis

the

character

usedbythe

DOS

to

fill

relative

recordsasthey

are

created,

beforeaprogram

fills

them

with

other

information.

Thus,ifwe

wanttowrite

the

last

recordweexpecttoneedinour

file

with

dummy

data

that will

not

interfere

with

our

later

work,

CHR$(255)isthe

obvious

choice.

Hereishowitworksinan

actual

program

which

you

may

copy

for

useinyour

own

relative

file

programs.

1020

OPEN

15,8,15

Open

command

channel

1380

INPUT"

ENTER

RELATIVE

FILE

NAME''

;FI$

Select

file

parameters

1390

INPUT"ENTER

MAX.#OF

RECORDS";NR

1400

INPUT-ENTER

RECORD

LENGTH";RL

59

1410OPEN

l,8,2,4t0:"+FI$+",L,"

1420

GOSUB

59990

1430RH=INT(NR/256)

1440RL=NR-256*RH

1450PRINT#15,t4P"

+

CHR$(96+2)

+

CHR$(RL)+CHR$(RH)

1460

GOSUB

59990

1470

PRINT#1,CHR$(255);

1480

GOSUB

59990

1490PRINT#15/'P"

+

CHR$(96+2)

+

CHR$(RL)+CHR$(RH)

1500

GOSUB

59990

1510

CLOSE

1

1520

GOSUB

59990

9980

CLOSE

15

9990

END

59980

REM

CHECK

DISK

SUBROUTINE

59990

INPUT#15,EN,EM$,ET,ES

60000IFEN>1

AND

ENO50

THEN

PRINT

EN,EM$,ET,ES:STOP

60010

RETURN

Begintocreate

desired

file

Check

for

disk

errors

Calculate

length

values

Positiontolast

record

number

Send

default

character

to

it

Re-position

for

safety

Now

the

file

canbesafely

closed

And

the

command

channel

closed

Beforeweend

the

pro

gram

Ignore

"RECORD

NOT

PRESENT"

Two

lines

require

additional

explanation.

When

line

1470

executes,

the

disk

drive

will

operate

forupto

tenormore

minutes,

creating

all

the

recordsinthe

file,upto

the

maximum

record

number

you

selectedinline

1390.

Thisisnormal,

and

only

needstobe

done

once.

During

the

process

you

may

hear

the

drive

motor

turning

andanoccasional

slight

clickasthe

head

steps

from

tracktotrack,

everything

is

probably

just

fine.

Second,

line

60000

aboveisdifferent

from

the

equivalent

lineinthe

error

check

subroutine

given

earlier.

Here

disk

error

number50is

specifically

ignored,

becauseitwillbegenerated

when

the

error

channelischecked

in line

1460.Weignoreitbecause

not

having

a

requested

record

would

onlybean

errorifthat

record

had

previously

been

created.

EXPANDINGARELATIVE

FILE

Whatifyou

underestimate

your

needs

and

needtoexpandarelative

file

later?

No

problem.

Simply

request

the

record

number

you

need,

evenifit

doesn't

currently

exist

in

the

file.

If

fthere

is

no

such

record

yet,

DOS'

will

create

it

as

soon

as

you

try

to

write

information

in

it,

and

also

automatically

create

any

other

missing

records

belowitin

number.

The

only

penalty

willbea

slight

time

delay

while

the

records

are

created.

60

WRITING

RELATIVE

FILE

DATA

The

commands

usedtoread

and

write

relative

file

data

are

the

same

Print#,

Input#,

and

Get#

commands

usedinthe

preceding

chapteronSequential

files.

Each

command

is

usedasdescribed

there.

However,

some

aspectsofrelative

file

accessdodiffer

from

sequential

file

programming,

andwewill

cover

those

differences

here.

DESIGNINGARELATIVE

RECORD

As

stated

earlierinthis

chapter,

each

relative

record

has a

fixed

length,

including

all

special

characters.

Within

that

fixed

length,

there

are

two

popular

waystoorganize

various

individual

fieldsofinformation.

Oneisfree-format,

with

individual

fields

varying

in

length

from

recordtorecord,

and

each

field

separated

from

the

nextbya

carriage

return

character

(eachofwhich

does

takeup1

character

spaceinthe

record).

The

other

approach

is

to

use

fixed-length

fields,

that

may

or

may

not

be

separated

by

carriage

returns.

If

fixed

length

fields

are

not

all

separated

by

carriage

returns,

you

will

either

needtobe

sure

a

carriage

returnisincluded

within

each88character

portionofthe record.Ifthisisnot

done,

you

will

havetouse

the

Get#

commandtoread

the

record,ata

significant

cost

in

speed.

Relative

recordsof88orfewer

characters,

or

final

portionsofrecords

that

are88or

fewer

characters

in

length,

need

not

end

inacarriage

return.

The

1541

is

smart

enough

to

recognize

the

endofa

relative

record

even

without a

finahcarriage

return.

Though

the

savingofa

single

character

isn't

much,

when

multiplied

by

the

numberofrecordsona

diskette,

the

savings

couldbesignificant.

Since

each

relative

record

mustbewrittenbya

single

Print#

statement,

the

recom

mended

approachisto

buildacopyofthe

current

recordinmemory

before

writingitto

disk.Itcanbecollected

intoasingle

string

variable

with

the

helpofBasic's

many

string-

handling

functions,

and

then

all

written

outatonce

from

that

variable.

Hereisan

example.Ifwe

are

writing

a

4-line

mail

label,

consisting

of4fields

named

"NAME",

"STREET",

"CITY&STATE",

and

"ZIP

CODE",

and

haveatotal

record

sizeof87

characters,

we

can

organizeitin

eitheroftwo

ways:

WITH

FIXED

LENGTH

FIELDS

WITH

VARIABLE

LENGTH

FIELDS

Field

Name

Length

Field

Name

Length

NAME

27

characters

NAME

31

characters

STREET

27

characters

STREET

31

characters

CITY&STATE

23

characters

CITY&STATE

26

characters

ZIP

CODE

10

characters

ZIP

CODE

11

characters

Total

length*87

characters

Potential

length

99

characters

Edited

length

87

characters

With

fixed

length

records,

the

field

lengths

addupto

exactly

the

record

length.

Since

the

total

lengthisjust

within

the

Input

buffer

size

limitation,

no

carriage

return

characters

are

needed.

With

variable

length

records,wecan

take

advantageofthe

variability

of

actual

address

lengths.

While

one

name

contains27letters,

another

may

have

only

15,

and

the

same

variability

existsinStreet

and

City

lengths.

Although

variable

length

records

lose1character

per

field

for

carriage

returns,

they

can

take

advantageofthe

difference

61

between

maximum

field

length

and

average

field

length.Aprogram

that

uses

variable

record

lengths

must

calculate

the

total

lengthofeach

recordasitisentered,tobe

sure

the

totalofall

fields

doesn't

exceed

the

space

available.

WRITING

THE

RECORD

Hereisan

exampleofprogram

linestoenter

variable

length

fields

for

the

above

file

design,

build

them

intoasingle

string,

and

send

themtorecord

numberREin

file

number

3

(assumedtobearelative

file

that

uses

channel

number

3).

150CR$=CHR$(13)

2000

INPUT4

4NAME";NA$

2010IFLEN(NA$)>30

THEN

2000

2020

INPUT4

'STREET"

;SA$

2030IFLEN(SA$)>30

THEN

2020

2040

INPUT44CITY&STATE";CS$

2050IFLEN(CS$)>25

THEN

2040

2060

INPUT4

4ZIP

CODE";ZP$

2070IFLEN(ZP$)>10

THEN

2060

2080

DAS=NA$+

CR$+SA$+

CR$

+

CS$+CR$+ZP$

2090IFLEN(DA$)<87

THEN

2120

2100

PRINT44RECORD

TOO

LONG"

2110

GOTO

2000

2120RH=INT(RE/256)

2130RL=RE-256*RH

2140

PRWT#15,44F'+CHR$(96

+3)+

CHR$(RL)+CHR$(RH)

2150

GOSUB

59990

2160PRINT#3,DA$

2170

GOSUB

59990

2180

PRINT#15,44P"

+CHR$(96+3)

+

CHR$(RL)+CHR$(RH)

2190

GOSUB

59990

Carriage

Return

Enter

fields

And

check

lengthofeach

Build

output

data

string

Check

its

length

If

too

long

overall

Calculate

record

number

Positiontorecord

number

RE

Check

for

disk

errors

Send

datatoit

Re-position

for

safety

To

use

the

above

program

lines

for

the

version

with

fixed

length

fields,wewould

alterafew

linesasfollows:

150

160BL$="

2000

INPUT44NAME";NA$

2005LN=LEN(NA$)

2010IFLEN(NA$)>27

THEN

2000

2015

NA$=NA$+LEFT$(BL$,27-LN)

2020

INPUT<4STREET";SA$

2025LN=LEN(SA$)

Not

needed

this

time

27

shifted

space

characters

Checking

for

different

lengths

And

paddingtopreset

sizes

62

2030IFLEN(SA$)>27

THEN

2020

2035

SA$=SA$+LEFT$(BL$,27-LN)

2040

INPUT"CITY&STATE";CS$

2045LN=LEN(CS$)

2050IFLEN(CS$)>23

THEN

2040

2055

CSS=CSS+LEFT$(BL$,23

-LN)

2060

ENfPUT'ZIP

CODE";ZP$

2065LN=LEN(ZP$)

2070IFLEN(ZP$)>10THEN

2060

2075

ZP$=ZP$+LEFT$(BL$,10-LN)

2080

DAS = NAS+SAS+CSS+ZPS

Note

lackofseparators

2120RH=INT(RE/256)

2130RL=RE-256*RH

2140PRINT#15,"P"+CHR$(96

+3)+

CHRS(RL)+CHRS(RH)+CHRS

(1)

2150

GOSUB

59990

2160

PRINT#3

,DA$;

Note

added

semicolon

2170

GOSUB

59990

2180

PRINT#

15,"P"+CHR$(96+3)

+

CHRS(RL)+CHRS(RH)+CHRS

(1)

2190

GOSUB

59990

If

field

contents

varyinlength,

variable

field

lengths

are

often

preferable.

On

the

other

hand,ifthe

field

lengths

are

stable,

fixed

field

lengths

are

preferable.

Fixed

length

fields

are

also

required

if

you

wanttouse

the

optional

offset

parameter

of

the

Record#

commandtopointata

particular

byte

withinarecord.

However,

one

warning

must

be

made

about

using

the

offset

this

way.

When

any

part

of a

recordiswritten,

DOS

overwrites

any

remaining

spacesinthe

record.

Thus,ifyou

must

use

the

offset

option,

never

update

any

fieldina

record

other

than

the

last

one

unless

all

succeeding

fields

will

alsobeupdated

from

memory

later.

The

above

programs

are

carefultomatch

record

lengths

exactlytothe

space

available.

Programs

that

don'tdoso

will

discover

that

DOS

pads

short

records

outtofull

size

with

fill

characters,

and

truncates

overlong

recordstofill

only

their

allotted

space.

Whenarecordistruncated,

DOS

will

indicate

error

51,''RECORD

OVERFLOW'',

but

short

records

willbeaccepted

withoutaDOS

error

message.

READINGARELATIVE

RECORD

Oncearelative

record

has

been

written

properlytodiskette,

readingitback

into

computer

memoryisfairly

simple,

but

the

procedure

again

varies,

dependingonwhether

it

uses

fixedorvariable

length

fields.

Here

are

the

program

lines

neededtoread

back

the

variable

fields

created

above

from

record

numberREin

file

and

channel

3:

3000RH=

INT(RE/256)

Calculate

record

number

3010RL=RE-256*RH

3020

PRINT#15,ttP"+CHR$(96

+3)+

CHRS(RL)+CHR$(RH)+CHRS

(1)

Position

to

record

number

RE

63

3030

GOSUB

59990 Check

for

disk

errors

3040

INPUT#1,NA$,SA$,CS$,ZP$

Readinfields

3050

GOSUB

59990

3060

PRINT#15,"P"

+CHR$(96+3)

+

CHR$(RL)+CHR$(RH)

Re-position

for

safety

Here

are

the

lines

neededtoread

back

the

version

with

fixed

length

fields:

3000RH=INT(RE/256)

3010RL=RE-256*RH

3020

PRINT#15,"P"

+

CHR$(96+3)+CHR$

(RL)+CHR$(RH)

3030

GOSUB

59990

3040

INPUT#1,DA$

Readinentire

record

3050

GOSUB

59990

3060

PRINT#15,"P"

+CHR$(96+3)

+

CHR$(RL)+CHR$(RH)

3070

NA$ =

LEFT$(DA$,27)

Split

data

into

fields

3080

SA$=MID$(DA$,28,27)

3090

CS$=MID$(DA$,55,23)

3100

ZP$=RIGHT$(DA$,

10)

This

ends

our

discussion

of

relative

files.Acomplete

"RELATIVE

FILE"

program,

similartothe

examplesinthis

chapter,

is

includedonthe

Test/Demo

diskette.

THE

VALUEOFINDEX

FILES

(ADVANCED

USERS)

In

the

last

two

chapterswehave

learned

howtouse

sequential

and

relative

files

separately.

But

they

are

often

used

together,

with

the

sequential

file

usedtokeep

brief

recordsofwhich

nameinthe

relative

fileisstoredineach

record

number.

That

way

the

contentsofthe

sequential

file

canberead

intoastring

array

and

sorted

alphabetically.

After

sorting,

a technique

knownasa

binary

search

canbeusedtovery

quickly

find

an

entered

nameinthe

array,

and

readinor

write

the

associated

recordinthe

relative

file.

Advanced

programs

can

maintain

twoormore

such

index

files,

sortedindiffering

ways

simultaneously.

64

CHAPTER

7

DIRECT

ACCESS

COMMANDS

A

TOOL

FOR

ADVANCED

USERS

Direct

access

commands

specify

individual

sectorsonthe

diskette,

reading

and

writing

information

entirely

under

your

direction.

This

gives

them

almost

complete

flexibility

in

data-handling

programs,

but

also

imposes tremendous

responsibilities

on

the

programmer,tobe

sure

nothing

goes

awry.Asa

result,

they

are

normally

used

only

in

complex

commercial

programs

abletoproperly

organize

data

without

help

from

the

disk

drive

itself.

A

far

more

common

use of

direct

access

commandsisin

utility

programs

used

to

view

and

alter

partsofthe

diskette

that

are

not

normally

seen

directly.

For

instance,

such

commands

canbeusedtochange

the

nameofa

diskette

without

erasing

allofits

programs,

to

lockaprogramsoit

can'tbeerased,orhide

your

nameina

location

where

it

won'tbeexpected.

DISKETTE

ORGANIZATION

There

areatotalof683

blocksona

1541

diskette,

of

which

664

are

available

for

use,

with

the

rest

reserved

for

the

BAM

(Block

Availability

Map)

and

the

Directory.

The

diskette's

surfaceisdivided

into

tracks,

which

are

laid

outasconcentric

circles

on

the

surfaceofthe

diskette.

There

are35different

tracks,

starting

with

track1at

the

outsideofthe

diskette

to

track35at

the

center.

Track18is

used

for

the

directory,

and

the

DOS

fillsupthe

diskette

from

the

center

outward,

alternately

in

both

directions.

Each

trackissubdivided

into

sectors

(also

called

blocks).

Because

thereismore

roomonthe

outer

tracks,

there

are

more

sectors

per

track

there.

The

outermost

tracks

contain21sectors

each,

while

the

innermost

ones

only

have17sectors

each.

The

table

below

shows

the

numberofsectors

per

track.

Table

6.1:

Track

and

Sector

Format

TRACK

NUMBER

1to17

18to24

25to30

31to35

SECTOR

NUMBERS

0

through

20

0

through

18

0

through

17

0

through

16

TOTAL

SECTORS

21

19

18

17

In

this

chapterwewill

describe

the

DOS

commands

for

directly

reading

and

writing

any

track

and

blockonthe

diskette,

as

wellasthe

commands

usedtomark

blocksasused

or

unused.

Unless

otherwise

notes,

all

direct

access

commands

are

the

sameinboth

Basic

2

and

Basic

3.5.

OPENINGADATA

CHANNEL

FOR

DIRECT

ACCESS

When

working

with

direct

access

data,

you-need

two

channels

opentothe

disk:

the

command

channel

we've

used

throughout

the

book,

and

another

for

data.

The

command

channelisopened

with

the

usual

OPEN

15,8,15orequivalent.

A

direct

access

data

65

channelisopened

much

like

other

files,

except

that

the

pound

sign

(#),

optionally

followedbya

memory

buffer

number,isusedasa

file

name.

FORMAT

FOR

DIRECT

ACCESS

FILE

OPEN

STATEMENTS:

OPEN

file

#,device#,channel#,"#buffer

#"

where

"file#"is

the

file

number,

"device#"is

the

disk's

device

number,

normally

8;

"channel#"is

the

channel

number,anumber

between2and14thatisnot

usedbyother

files

open

at

the

same

time;

and

"buffer

#",

if

present,

isa0,

1,

2,

or

3,

specifying

the

memory

buffer

within

the

1541touse

for

this

file's

data.

EXAMPLES:

Ifwedon't

specify

which

disk

buffertouse,

the

1541

will

select

one:

OPEN5,8,5,"#"

Orwecan

make

the

choice

ourselves:

OPEN4,8,4,"#2"

BLOCK-READ

The

purpose ofaBlock

Readisto

load

the

contentsofa

specified

sector

into

a

file

buffer.

Although

the

Block

Read

command

(B-R)isstill

partofthe

DOS,

command

set,itis

nearly

always

replacedbytheUlcommand.

FORMAT

FOR

THE

BLOCK-READ

COMMAND:

PRINT#15,

"Ul";

channel#;drive#;track#;sector

#

where

"channel#"is

the

channel

number

specified

when

the

file

into

which

the

block

willberead

was

opened,

"drive#"is

the

drive

number,

always0on

the

1541,

and

"track#"and

"sector#"are

respectively

the

track

and

sector

numbers

containing

the

desired

blockofdatatobe

read

into

the

file

buffer.

ALTERNATE

FORMATS:

PRINT#15,"Ul:"channel

#;drive

#;track

#;sector

#

PRINT#15,"UA:"channel

#;drive

#;track

#;sector

#

PRINT#15,"Ul:channel

#,drive

#,track

#,sector

#"

66

EXAMPLE:

Hereisa

complete

programtoread a

sector

into

disk

memory

using

Ul,

and

from

there

into

computer

memory

via

Get#.

(Ifacarriage

return

will

appearatleast

once

in

every88characters

of

data,

Input#

may

be usedinplaceofGet#).

110

MB=7936:REM

$1FOO

Defineamemory

buffer

120

INPUT"TRACKTOREAD";T

Selectatrack

130

INPUT-SECTORTOREAD";S

and

sector

140

OPEN

15,8,15

Open

command

channel

150

OPEN

5,8,5,"#"

Open

direct

access

channel

160

PRINT#15,"Ul";5;0;T;S

Read

sector

into

disk

buffer

170

FORI=

MB

TO

MB+255

Usealoop

to

180

GET#5,A$:IFA$=""

copy

disk

buffer

THENA$=

CHR$(0)

into

computer

memory

190

POKE

I,ASC(A$)

Tidyupafter

200

CLOSE

5:CLOSE

15

220

END

As

the

loop

progresses,

the

contentsofthe

specified

track

and

sector

are

copied

into

computer

memory,

beginningatthe

address

setbyvariableMBin

line

160,

and

may

be

examined

and

altered

there.

Thisisthe

basis

for

programs

like

"DISPLAYT&

S"onthe

Test/Demo

diskette.

BLOCK-WRITE

The

purpose

of a

Block

Writeisto

save

the

contentsofa

file

buffer

intoaspecified

sector.

It is

thus

the

reverseofthe

Block

Read

command.

Although

the

Block

Write

command

(B-W)isstill

partofthe

DOS

command

set,itis

nearly

always

replacedbythe

U2

command.

FORMAT

FOR

THE

BLOCK-WRITE

COMMAND:

PRINT#15,"U2'';channel

#;drive

#;track

#;sector

#

where

"channel#"is

the

channel

number

specified

when

the

file

into

which

the

block1

willberead

was

opened;

"drive#"is

the

drive

number

(always0on

the

1541);

and

"track#"and

"sector#"are

respectively

the

track

and

sector

numbers

that

should

receive

the

blockofdata

being

saved

from

the

file

buffer.

ALTERNATE

FORMATS:

PRINT#15,'4U2:''channel

#;drive

#;track

#;sector

#

PRINT#15,"UB:"channel

#;drive

#;track

#;sector

#

PRINT#15,"U2:channel

#,drive

#,track

#,sector

#"

67

EXAMPLES:

To

restore

track

18,

sector1of

the

directory

from

the

disk buffer

filledbythe

Block

Read

exampleonpage

82,wecan

use

PRlNT#15,"U2";5;0;18;l

We'll

returntothis

exampleonthe

afterwelearntoalter

the

directory

in

a

useful

way.

We

can

also

useaBlock

WritetowriteanameinTrack1,Sector1,a

rarely-used

sector.

This

canbeusedasa

wayofmarkingadisketteasbelongingtoyou.

Hereisa

programtodo

it,

using

the

alternate

formofthe

Block

Write

command:

110

INPUT"YOUR

NAME"

;NA$

Enteraname

120

OPEN

15,8,15

Open

command

channel

130

OPEN

4,8,4,4t#"

Open

direct

access

channel

140

PRINT#4,NA$

Write

nametobuffer

150

PRINT#15,4tU2";4;0;l;l

Write

buffertoTrack

1,

160

CLOSE

4

Sector1of

diskette

170

CLOSE

15

Tidyupafter

180

END

THE

ORIGINAL

BLOCK-READ

AND

BLOCK-WRITE

COMMANDS

(EXPERT

USERS

ONLY)

Although

the

Block

Read

and

Block

Write

commands

are

nearly

always

replaced

by

theUlandU2commands

respectively, the

original

commands

can

stillbeused,aslong

as

you

fully

understand

their

effects.

UnlikeUland

U2,

B-R

and

B-W

allow

youtoread

or

write

less

than a

full

sector.Inthe

caseofB-R,

the

first

byteofthe

selected

sector

is

usedtoset

the

buffer

pointer

(see

and

determines

how

many

bytesofthat

sector

are

read

intoadisk

memory

buffer.Aprogram

may

checktobe

sureitdoesn't

attempttoread

past

the

endofdata

actually

loaded

into

the

buffer,bywatching

for

the

valueofthe

file

status

variableSTto

change

from0to

64.

When

the

bufferiswritten

back

to

diskettebyB-W,

the

first

byte

writtenisthe

current

valueofthe

buffer

pointer,

and

only

that

many

bytes

are

written

into

the

specified

sector.

B-R

and

B-W

may

thus

be

usefulinworking

with

custom-designed

file

structures.

FORMAT

FOR

THE

ORIGINAL

BLOCK-READ

AND

BLOCK-WRITE

COM

MANDS:

PRINT#15,4tBLOCK-READ'';channel

#;drive

#;track

#;sector

#

abbreviated

as:

PRINT#15,"B-R";channel

#;drive

#;track

#;sector

#

and

PRINT#15,ttBLOCK-WRITE*';channel

#;drive

#;track

#;sector

#

68

abbreviated

as:

PRINT#15,"B-W";channel

#;drive

#;track

#;sector

#

where

"channel#"is

the

channel

number

specified

when

the

file

into

which

the

block

willberead

was

opened,

"drive#"is

the

drive

number

(always0on

the

1541),

and

44track#"and

"sector#"are

respectively

the

track

and

sector

numbers

containing

the

desired

blockofdatatobe

partially

read

intoorwritten

from

the

file

buffer.

IMPORTANT

NOTES:

1.Ina

true

Block-Read,

the

first

byteofthe

selected

sectorisused

to

determine

how

many

bytesofthat

sectortoread

into

the

disk

memory

buffer.

It

thus

cannotbeusedtoreadanentire

sector

into

the

buffer,asthe

first

data

byte

is

always

interpreted as

being

the

numberofcharacters

to

read,

rather

than

partofthe

data.

2.

Similarly,

inatrue

Block-Write,

when

the

bufferiswritten

backtodiskette,

the

first

byte

writtenisthe

current

valueofthe

buffer

pointer,

and

only

that

many

bytes

are

written

into

the

specified

sector.Itcannot

be usedtorewriteanentire

sector

onto

diskette

unchanged,

because

the

first

data

byteisoverwritten

by

the

buffer

pointer.

THE

BUFFER

POINTER

The

buffer

pointer pointstowhere

the

will

begin

withinadisk

memory

buffer.Bymoving

the

buffer

pointer,

you

can

access

individual

bytes

within

a

blockinany

order.

This

allows

youtoedit

any

portionofa

sector,

or organizeitinto

fields,

likearelative

record.

FORMAT

FOR

THE

BUFFER-POINTER

COMMAND:

PRINT#15,<4BUFFER-POINTER";channel#;byte

usually

abbreviated

as:

PRINT#15,"B-P";channel

#;byte

where

"channel#"is

the

channel

number

specified

when

the

file

reserving

the

buffer

was

opened,

and

"byte"isthe

character

number

within

the

bufferatwhichtopoint.

ALTERNATE

FORMATS:

PRINT#15,"B-P:"channel

#;byte

PRINT#15,"B-P:channel

#;byte"

EXAMPLE:

Hereisa

program

that

locks

the

first

programorfileona

1541

diskette.

It

works

by

reading

the

startofthe

directory

(Track

18,

Sector1)into

disk

memory,

setting

the

buffer

69

pointertothe

first file

type

byte

(see

AppendixCfor

detailsofdirectory

organization),

lockingitby

setting

bit6and

rewriting

it.

110

OPEN

15,8,15

Open

command

channel

120

OPEN

5,8,5,"#"

Open

direct

access

channel

130

PRINT#15,"Ul";5;0;18;l

Read

Track

18,

Sector

1

140

PRINT#15,"B-P";5;2

PointtoByte

2 of

the

buffer

150

GET#5,A$:IF

A$=""THENA$=

CHR$(0)

Readitinto

memory

160A=

ASC(A$)OR64

Turnonbit6to

lock

170

PRINT#15,"B-P";5;2

PointtoByte2again

180

PRINT#5,CHR$(A);

Overwrite

itinbuffer

190

PRINT#15,"U2";5;0;18;l

Rewrite

buffer

to diskette

200

CLOSE

5

Tidyupafter

210

CLOSE

15

220

END

After

the

above

programisrun,

the

first

fileonthat

diskette

cannolongerbeerased.

If

you

later

needtoerase

that

file,

re-run

the

same

program,

but

substitute

the

revised

line

160

belowtounlock

the

file

again:

160A=

ASC(A$)

AND

191

Turn

off

bit6to

unlock

ALLOCATING

BLOCKS

Once

you

have

written

something

inaparticular

sectorona

diskette

with

the

help

of

direct

access

commands,

you

may

wishtomark

that

sectoras"already

used,"tokeep

other

files

from

being

written

there.

Blocks

thus

"allocated"

willbesafe

until

the

diskette

is

validated.

FORMAT

FOR

BLOCK-ALLOCATE

COMMAND:

PRINT#15,<tBLOCK-ALLOCATE";drive

#;

track

#;sector

#

usually

abbreviated

as:

PRINT#15,"B-A";drive

#;

track

#;sector

#

where

"drive#"is

the

drive

number,

always0on

the

1541,

and

"track#"and

"sector

#"

are the

track

and

sector

containing

the

block

of

data

to

be

read

into

the

file

buffer.

ALTERNATE

FORMAT:

PRINT#15,"B-A:";drive

#;

track

#;sector

#

EXAMPLE:

If

you

trytoallocate

a

block

that

isn't

available,

the

DOS

will

set

the

error

message

to

number

65,NOBLOCK,

and

set

the

track

and

block

numbersinthe

error

message

to

70

the

track

and

block

number.

Therefore,

before

selecting

a

blocktowrite,

trytoallocate

that

block.Ifthe

block

isn't

available;

read

the

block

from

the

error

channel

and

allocate

it

instead.

However,donot

allocate

data

blocksinthe

directory

track.Ifthe

track

number

returned

is0,the

diskette

is

full.

Hereisa

program

that

allocates

a

placetostoreamessageona

diskette.

100OPEN15,8,15

110OPEN5,8,5,"#"

120

PRINT#5,"I

THINK

THEREFOREIAM"

130T=l:S=l

140

PRINT#15,"B-A";0;T;S

150

INPUT#15,EN,EM$,ET,ES

160IFEN=0

THEN

210

170IFENO65

THEN

PRINT

EN,EM$,ET,ES:STOP

180IFET=0

THEN

PRINT

"DISK

FULL":STOP

190IFET=18THEN

ET=

19:ES=0

200

T =

ET:S=ES:GOTO

140

210

PRINT#15,"U2";5;0;T;S

220

PRINT

"STORED

AT:",T,S

230

CLOSE

5:CLOSE

15

240

END

FREEING

BLOCKS

Open

command

channel

**

direct

access

"

Writeamessagetobuffer

Startatfirst

track§or

Try

allocating

it

Seeifit

worked

If

so,

we're

almost

done

"NO

BLOCK"

means

already

allocated

If

we're

outofroom

Don't

allocate

the

directory!

Try

suggested

track§or

buffertoallocated

sector

Say

where

message

went

and

tidy

up

The

Block-Free

commandisthe

opposite

of

Block-Allocate.

It

freesablock

that

you

don't

need

any

more,

for

re-usebythe

DOS.

Block-Free

updates

the

BAMtoshow

a

particular

sectorisnotinuse,

rather

than

actually

erasing

any

data.

FORMAT

FOR

BLOCK-FREE

COMMAND:

PRINT#15,"BLOCK-FREE'';drive

#;track

#;sector

#

abbreviated

as:

PRINT#15,"B-F";drive

#;track

#;sector

#

where

"drive#"is

the

drive

number

(always0on

the

1541),

and

"track#"and

"sector

#"

are

respectively

the

track

and

sector

numbers

containing

the

desired

blockofdata

to

be

read

into

the

file

buffer.

ALTERNATE

FORMAT:

PRINT#15,"B-F:";drive

#;track

#;sector

#

71

EXAMPLE:

To

free

the

sectorinwhichwewrote

our

nameinthe

Block

Write

example,

and

allocated

in

the

first

Block-Allocate

example,wecould

use

the

following

command:

PRINT#15,"B-F";0;l;l

USING

RANDOM

FILES

(ADVANCED

USERS

ONLY)

By

combining

the

commands

in

this

chapter,

it

is

possible to

developafile-

handing

program

that

uses

random

files.

What

you

need

to

know

now

is

how

to

keep

track

of

which

blocks

on

the

disk

suchafile

has

used.

(Even

though

you

know

a

sector

has

not

been

allocated

by

your

random

file,

you

must

alsobesureitwasn't

allocated

by

another

unrelated

fileonthe

diskette.)

The

most

common

wayofrecording

which

sectors

have

been

usedbya

random

file

is

inasequential

file.

The

sequential

file

storesalistofrecord

numbers,

with

the

track,

sector,

and

byte

locationofeach

record.

This

means

three

channels

are

neededbya

random

file:

one

for

the

command

channel,

one

for

the

random

data,

and

the

last

for the

sequential

data.

72

CHAPTER

8

INTERNAL

DISK

COMMANDS

Expert

programmers

can

give

commands

that

directly

alter

the

workings.pf

the

1541,

muchasskilled

programmers

can

alter

the

workingsofBasic

inside

the

computer

with

Peeks,

Pokes

and

Sys

calls.Itis

also

possibletowrite

machine

language

programs

that

load

and

run

entirely

within

the

1541,

eitherbywriting

them

into

disk

memory

from

the

computer,orby

loading

them

directly

from

diskette

into

the

desired

disk

memory

buffer.

In

use,

thisissimilartoloading

and

running

machine

language

programsinyour

computer.

As when

learningtouse

Peek(),

Poke

and

Sysinyour

computer,

extreme

caution

is

advisedinusing

the

commandsinthis

chapter.

They

are

essentially

machine

language

commands,

and

lack

allofBasic's

safeguards.

If

anything

goes

wrong,

you

may

have

to

turn

the

disk

drive

off

andonagain

(after

removing

the

diskette)

to

regain

control.Donot

practice

these

commandsonany

important

diskette.

Rather,

makeaspare

copy and

work

with

that.

Knowing

howtoprograma6502inmachine

language

will

help

greatly,

and

you

will

also

needagood

memory

mapofthe

1541.Abrief

1541

map

appears

below.

Location

0000-00FF

0100-01FF

0200-02FF

0300-07FF

1800-180F

1C00-1C0F

C100-F258

F259-FE66

FE67-FE84

FE85-FEE6

FEE7-FF0F

FFE6-FFFF

1541

MEMORY

MAP

Purpose

2KofRAM

memory

Zero

page

work

area:

job queue,

important

variables

&

pointers

Stack

work

area

Command

buffers&tables:

channels,

parser,

output,

variables

Data

buffers

0-4,1per

pageofmemory.

Input/Output

chips

6522

VIA:

I/Otocomputer

65?2

VIA:

I/Otodisk

controller

Disk

Operating

System

ROM

Interface

Processor:

receive&interpret

commands

from

computer

Floppy

Disk

Controller:

executes

IP's

commands,

controls

mecha

nism

IRQ

handler:

switches

fromIPto

FDC&back

every10ms.

ROM

tables&constants

Patch

area

JMP

table:

User

command

vectors

73

Other

Resources:

More

detailed

information

about

Commodore

disk

drives

canbefoundinthese

books:

Inside

Commodore

DOS,byImmers&Neufeld

(Datamost,

cl984)

The

Anatomyofthe

1541

Disk

Drive,byEnglisch&Szczepanowski

(Abacus,

cl984)

Programming

the

PET/CBM,byWest

(Level

Limited,

cl982)

The

PET

Personal

Computer

Guide,byOsborne&Strasmas

(Osborne/McGraw-Hill,

c

1982)

MEMORY-READ

The

disk

contains

16KofROM

(Read-Only

Memory),aswellas2KofRAM

(Read-

Write

Memory).

You

can

get

direct

accesstoany

location

within

these,orto

the

buffers

that

the

DOS

has

setupin

RAM,byusing

memory

commands.

Memory-Read

allows

you

to

select

which

byteorbytestoread

from

disk

memory

into

the

computer.

The

Memory-

Read

commandisthe

equivalent

of

.the

Basic

Peek()

function,

but

reads

the

disk's

memory

insteadofthe

computer's

memory.

Note:

Unlike

other

disk

commands,

thoseinthis

chapter

cannotbespelled

out

in

full.

Thus,MRis

correct,

but

MEMORY-READisnotapermitted

alternate

wording.

FORMAT

FOR

THE

MEMORY-READ

COMMAND:

PRINT#15,t4M-R"CHR$(<address)CJ4R$(>address)CHR$(#

of

bytes)

where

"<address"isthe

low

order

pari,

and

">address"isthe

high

order

partofthe

addressindisk

memorytobe

read.Ifthe

optional

t4#ofbytes"isspecified,

it

selects

'how

many

memory

locations

will

be

read

in,

from

1-255.

Otherwise,

1

character

will

be

read.Ifdesired,

a

colon

(:)

may

follow

M-R

inside

the

quotation

marks.

ALTERNATE

FORMAT:

PRINT#15,t4M-R:"CHR$(<address)CHR$(>address)CHR$(#

of

bytes)

The

read

using

the

Get#

statement

through channel

#15

(the

error

channel),

will

be

from

that

address

in

the

disk

controller's

memory,

and

successive

bytes

willbefrom

successive

memory

locations.

Any

Input#

from

the

error

channel

will

give

peculiar

results

when

you're

using

this

command.

This

can be

clearedupby

sending

any

other

commandtothe

disk,

except

another

memory

command.

74

EXAMPLES:

To

see

how

many

tries

the

disk

will

maketoreadaparticular

sector,

and

whether

"seeks"

one-half

tracktoeach

side

willbeattemptedifa

read

fails,

and

whether

t4bumps"totrack

one

and

back

willbeattempted

before

declaring

the

sector

unreadable,

we

can*use

the

following

lines.

They

will

readaspecial

variable

in

the

zero

pageofdisk

memory,

called

REVCNT.Itis

locatedat$6A

hexadecimal

($6A

hexadecimal

=

6x16

+

10=106).

110

OPEN

15,8,15

120

PRINT#

15,''M-R"CHR$(

106)CHR$(0)

130

GET#15,G$:IFG$=""THENG$=

CHR$(0)

140G=ASC(G$)

150B=GAND

128:B$="ON":IFBTHENB$=

"OFF"

160S=GAND

64:S$="ON":IFSTHENS$=

"OFF"

170

T =GAND

31:PRINT"#OF

TRIES

IS";T

180

PRINT

"BUMPS

ARE";B$

190

PRINT

"SEEKS

ARE";S$

200

CLOSE

15

210

END

Open

command

channel

SameasG=PEEK(106)

Check

bit

7

Check

bit

6

Check

bits

0-5

and

give

results

Tidyupafter

Here'samore

general

purpose

program

that

reads

oneormore

locations

anywhereindisk

memory:

110OPEN15,8,15

120

INPUT"#OFBYTESTOREAD(0=

END)";NL

130IFNL<1

THEN

CLOSE

15:END

140IFNL>255THEN120

150

INPUT"STARTINGATADDRESS";AD

160AH=

INT(AD/256):AL

=

AD-AH*256

170PRINT#15,"M-R"CHR$(AL)CHR$(AH)

CHR$(NL)

180

FOR

1=1TONL

190:GET#15,A$:IFA$=""THENA$=

CHR$(0)

200:

PRINT

ASC(A$);

210

220

PRINT

230

GOTO

120

Open

command

channel

Enter

numberofbytes

wanted

unless

done

or

way

outofline

Enter

starting

address

Convertitinto

disk

form

Actual

Memory-Read

Loop

til

have

all

the

data

printingitaswego

Forever

MEMORY-WRITE

The

Memory-Write

commandisthe

equivalent

of

the

Basic

Poke

command,

but

has

its

effectindisk

memory

insteadofwithin

the

computer.

M-W

allows

youtowriteupto

34

bytesata

time

into

disk

memory.

The

Memory-Execute

and

some

User

commands

can

be

usedtorun

any

programs

written

this

way.

75

FORMAT

FOR

THE

MEMORY-WRITE

COMMAND:

PRINT#

15,*'M-W'CHR$(<address)CHR$(>address)CHR$

(#ofbytes)CHR$(data

byte(s))

where

"<address"isthe

low

order

part,

and

t4>address"

is

the

high

order

partofthe

addressindisk

memorytobegin

writing,

*'#ofbytes"isthe

numberofmemory

locations

that willbewritten

(from

1-34),

and

"data

byte"is1ormore

byte valuestobe

written

into

disk

memory,

eachasa

CHR$()

value.Ifdesired,

a

colon

(:)

may

follow

M-

W

within

the

quotation

marks.

ALTERNATE

FORMAT:

PRINT#

15/

'M-W:'

'CHR$(<address)CHR$(>address)CHR$

(#ofbytes)CHR$(data

byte(s))

EXAMPLES:

We

can

use

this

linetoturn

off

the

"bumps"

when

loading

DOS-protected

programs

(i.e.,

programs

that

have

been

protected

against

being

copiedbycreating

and

checking

for

specific

disk

errors).

PRINT#15,ttM-W"CHR$(106)CHR$(0)CHR$(l)CHR$(133)

The

following

line

can

be.usedtorecover

bad

sectors,

suchaswhenanimportant

file

has

been

damaged

and

cannotberead

normally.

PRINT#15,ttM-W"CHR$(106)CHR$(0)CHR$(l)CHR$(31)

The

above

two

examples

maybevery

useful

under

some

circumstances.

They

are

the

equivalent

of

POKE

106,133

and

POKE

106,31

respectively,

butindisk

memory,

not

inside

the

computer.Asmentionedinthe

first

example,

location

106

in

the

1541

disk

drive

signifies

three

separate

activities

to

the

drive,

all

error

recovery.

Bit7(the

high

bit),ifset

meansnobumps

(don't

thump

the

drive

backtotrack

1).

Bit6,if

set,

meansnoseeks.Inthat

case,

the

drive

won't

attempttoread

the

half-track

above

and

below

the

assigned

tracktoseeifit

can

read

the

data

that

way.

The

bottom

6

bits

are

the

countofhow

many

times

the

disk

will

trytoread

each

sector

before

and

after

trying

seeks

and

bumps

before

giving

up.

Since31is

the

largest

number

that

can

be

expressed

in6bits,

thatisthe

maximum

numberoftries

allowed.

From

this

example,

you

can

see

the

valueofknowing

something

about

Peeks,

Pokes,

and

machine-language

before

using

direct-access

disk

commands,aswellastheir

poten

tial

power.

76

MEMORY-EXECUTE

Any

routineindisk

memory,

eitherinRAMorROM,

canbeexecuted

with

the

Memory-Execute

command.Itis

the

equivalent

of

the

Basic

Sys

calltoa

machine

language

programorsubroutine,

but

worksindisk

memory

insteadofwithin

the

com

puter.

FORMAT

FOR

THE

MEMORY-EXECUTE

COMMAND:

PRINT#15,4tM-E"CHR$(<address)CHR$(>address)

where

"<address"

is

the

low

order

part,

and

">address"

is

the

high

order

partofthe

addressindisk

memoryatwhich

execution

istobegin.

ALTERNATE

FORMAT:

PRINT#15/<M-E:"CHR$(<address)CHR$(>address)

EXAMPLE:

Hereisa

Memory-Execute

command

that

does

absolutely

nothing.

The

first

instruc

tionitexecutesisan

RTS,

which

ends

the

command:

PRIOT#15,"M-E"CHR$(88)CHR$(242)

A

more

plausible

use

for

this

command

would

be

to

artificially

trigger

an

errat

message.

Don't

forgettocheck

the

error

channel,oryou'll

miss

the

message:

PRIOT#15,''M-E"CHR$(201)CHR$(239)

However,

most

uses

require

intimate

knowledgeofthe

inner

workingsofthe

DOS,

and

preliminary

setup

with

other

commands,

suchasMemory-Write.

BLOCK-EXECUTE

This

rarely-used

command

will

loadasector

containing

a

machine

language

routine

intoamemory

buffer

from

diskette,

and

executeitfrom

the

first

location

within

the

buffer,

untilaReTurn

from

Subroutine

(RTS)

instruction

ends

the

command.

FORMAT

FOR

THE

BLOCK-EXECUTE

COMMAND:

PRINT#15,"B-E'';channel

#;drive

#;track

#;sector

#

where

"channel#"is

the

channel

number

specified

when

the

file

into

which

the

block

willbeloaded

was

opened,

"drive#"is

the

drive

number

(always0on

the

1541),

and

"track#"and

"sector#"are

respectively

the

track

and

sector

numbers

containing

the

desired

block of

datatobe

loaded

into

the

file

buffer

and

executed

there.

77

ALTERNATE

FORMATS:

PRINT#15,44B-E:'';channel

#;drive

#;track

#;sector

#

PRINT#15,44B-E:channel

#,drive

#,track

#,sector

#"

EXAMPLES:

Assuming

you've

writtenamachine

language

program

onto

Track1,Sector8of

a

diskette,

and

would

liketorunitin

buffer

number1in

disk

memory

(starting

at

$0400

hexadecimal,

you

coulddosoasfollows:

110

OPEN

15,8,15

Open

command

channel

120

OPEN

2,8,2,44#1"

Open

direct

access

channeltobuffer

1

130PRINT#15,44B-E";2;0;l;8

LoadTrack1,Sector8init&

execute

140

CLOSE

2

Tidyupafter

150

CLOSE

15

160

END

USER

COMMANDS

Most

User

commands

are

intendedtobe

usedasmachine

language

JMP

or Basic

SYS

commandstomachine

language

programs

that

reside inside

the

disk

memory.

However,

someofthem

have

other

usesaswell.

The

Userl

and

User2

commands

are

used

to

replace

the

Block-Read

and

Block-Write

commands,UIre-starts

the

1541

without

changing

its

variables,

UJ

cold-starts

the

1541

almostasifithad

been

turned

off

and

on

again,

and

UI-

speedsupthe

1541

when

used

with

the

VIC20only.

(Note:

VIC20owners

don't

havetouse

UI-;

the

1541

works

with

the

VIC

20,

withorwithout

this

command.)

User

Command

Function

UIorUA

replaces

Block-Read

U2orUB

replaces

Block-Write

U3orUC

JMP

$0500

(sameasSYS

5*256,

but

within

the

1541

itself.)

U4orUD

JMP

$0503

(SYS

5*256+3)

U5orUE

JMP

$0506("

5*256+6)

U6orUF

JMP

$0509

(*'

5*256+9)

U7orUG

JMP

$050C(4<

5*256

+12)

U8

or

UH

JMP

$050F

(t4

5*256+15)

U9

or

UI

1541

NMI

(non-maskable

interrupt—warm

start)

U:

or

UJ

1541

reset

(cold

start,

allow2seconds

before

UI+

restore

1541tousual

speed

UI-

speed

1541

up

by

25%

when

used

with

VIC

20

only.

By

loading

these

memory

locations

with

another

machine

language

JMP

command,

such

as

JMP

$0520,

you

can

create

longer

routines

that

operate

in

the

disk's

memory

along

withaneasy-to-use

jump

table.

78

FORMAT

FOR

USER

COMMANDS:

PRINT#15,<<Ucharacter"

where

"character"

defines

oneofthe

preset

user

commands

listed

above.

EXAMPLES:

PRINT#15,"U:"

Preferred

formofDOS

RESET

command

PRINT#15,"U3"

Execute

programatstartofbuffer

2

79

CHAPTER

9

MACHINE

LANGUAGE

PROGRAMS

Hereisa

listofdisk-related

Kernal

ROM

subroutines

andapractical

exampleoftheir

useina

program

which

readsasequential

file

into

memory

from

disk.

Note

that

most

require

advance

setupofoneormore

processor

registers

or

memory

locations,

and

all

are

"■called

with

the

assembly

language

JSR

command.

Foramore

complete

description

astowhat

each

routine

does

and

how

parameters

are

set

for

each

routine,

see

the

Programmer's

Reference

Guide

for

your

specific

computer.

DISK-RELATED

KERNAL

SUBROUTINES

Label

Address

Function

SETLFS

SETNAM

OPEN

CLOSE

CHKIN

CHKOUT

CLRCHN

CHRIN

CHROUT

START

=

LDA

LDX

LDY

JSR

LDA

LDX

LDY

JSR

LDX

JSR

BEQ

JSR

JMP

LDA

JSR

RTS

$FFBA

$FFBD

$FFC0

$FFC3

$FFC6

$FFC9

$FFCC

$FFCF

$FFD2

#4

#<FNADR

#>FNADR

SETNAM

#3

#8

#0

SETLFS

OPEN

#3

CHKIN

CHRIN

END

CHROUT

CLOSE

CLRCHN

;SET

LOGICAL,

FIRST&SECOND

ADDRESSES

;SET

LENGTH&ADDRESSOFFILENAME

;OPEN

LOGICAL

FILE

;CLOSE

LOGICAL

FILE

;SELECT

CHANNEL

FOR

INPUT

;SELECT

CHANNEL

FOR

OUTPUT

;CLEAR

ALL

CHANNELS&RESTORE

DEFAULT

I/O

;GET

BYTE

FROM

CURRENT

INPUT

DEVICE

;OUTPUT

BYTETOCURRENT

OUTPUT

DEVICE

;SET

LENGTH&ADDRESS

;OF

FILE

NAME,

LOW

;&

HIGH

BYTES

;FOR

NAME

SETTER

;SET

FILE

NUMBER,

;DISK

DEVICE

NUMBER,

;AND

SECONDARY

ADDRESS

;AND

SET

THEM

;OPEN

3,8,0,t4TEST"

;SELECT

FILE3FOR

INPUT

;GET

FROM

FILE

;UNTIL

FINISHORFAIL

;OUTPUT

BYTETOSCREEN

;AND

LOOP

BACK

FOR

MORE

;WHEN

DONE

;CLOSE

FILE

;RESTORE

DEFAULT

I/O

;BACKTOBASIC

FNADR

.BYT

"TEST"

;STORE

FILE

NAME

HERE

80

APPENDIX

A:

CHANGING

THE

DEVICE

NUMBER

SOFTWARE

METHOD

One

waytotemporarily

change

the

device

numberofa

disk

driveisviaaprogram.

When

powerisfirst

turned

on,

the

drive

readsanI/O

location

whose

valueiscontrolled

byajumperonits

circuit

board,

and

writes

the

device

numberitreads

there

into

memory

locations

119 and

120.

Any

time

thereafter,

you

may

write

over

that

device

number

with

a

new

one,

which

willbeeffective

untilitis

changed

again,orthe

1541isreset.

FORMAT

FOR

TEMPORARILY

CHANGING

THE

DISK

DEVICE

NUMBER:

PRINT#15,''M-W"CHR$(119)CHR$(0)CHR$(2)CHR$

(device#+

32)CHR$(device

#+64)

EXAMPLE:

Hereisa

program

that

sets

any

device

number

from

8-11:

10

INPUT'NEW

DEVICE

NUMBER';DV

20IFDV<8

OR

DV>11

THEN

10

30

OPEN

15,8,15

40

PRINT#15,"M-W"CHR$(119)CHR$(0)CHR$(2)CHR$(DV

+

32)CHR$(DV+64)

50

CLOSE

15

Note:

If

you

will

be

using

two

disk

drives,

and

want

to

temporarily

change

the

device

numberofone,

you

will

needtorun

the

above

program

with

the

disk

drive

whose

device

numberisnottobe

changed

turned

off.

After

the

program

has

been

run,

you

may

turn

that

drive

back

on.Ifyou

needtoconnect

more

than

two

drives

at

once,

you

will

needtouse

the

hardware

methodofchanging

device

numbers,

although

you

maybeabletogetbyinanemergencybyunplugging

the

serial

bus

cable

from

drives

whose

device

number

has

already

been

set

while

changing

others.

Thisisnot

recommended,

however,asthereisalways

dangerofdamaging

electronic

devices

when

pluggingincables

with

the

power

on.

81

STEPS

TO

CHANGE

THE

DEVICE

NUMBER

USING

THE

SWITCH

1.

Turn

off

the

disk

drive.

2.

Refertothe

following

charttoset

the

DIPSWat

the

backofthe

disk

drive

for

device

number

setting.

Device

#

swl

sw2

8

9

10

11

ON

OFF

ON

OFF

ON

OFF

3.

Turn on

the

disk

drive.

82

APPENDIX

B:

DOS

ERROR

MESSAGES

AND

LIKELY

CAUSES

Note:

Many

commercial

program

diskettes

are

intentionally

created

with

one

or

moreofthe

following

errors,tokeep

programs

from

being

improperly

duplicated.

Ifadisk

error

occurs

while

you

are

makingasecurity

copyofa

commercial

program

diskette,

check

the

program's

manual.Ifits

copyright

statement

does

not

permit

purchasers

to

copy

the

program

for

their

own

use,

you

may

notbeable

to

duplicate

the

diskette.

In

some

such

cases,asafety

spare

copyofthe

program

diskette

is

available

from

your

dealerordirectly

from

the

company

forareasonable

fee.

00:

OK

(notanerror)

Thisisthe

message

that

usually

appears

when

the

error

channelischecked.

It

means

thereisno

current

errorinthe

disk

unit.

01:.FILES

SCRATCHED

(notanerror)

Thisisthe

message

that

appears

when

the

error

channelischecked

after

using

the

Scratch

command.

The

track

number

tells

how

many

files

were

erased.

NOTE:Ifany

other

error

message

numbers

less

than20ever

appear,

they

may

be

ignored.

All

true

errors

have

numbersof20ormore.

20:

READ

ERROR

(block

header

not

found)

The

disk

controller

is

unabletolocate

the

header of

the

requested

data

block.

Causedbyan

illegal

block,ora

header

that

has

been

destroyed.

Usually

unrecoverable.

21:

READ

ERROR

(no

sync

character)

The

disk

controller

is

unabletodetectasync

markonthe

desired

track.

Causedbymisalignment,

oradiskette

thatisabsent,

unformatted

or

improperly

seated.

Can

also

indicate

hardware

failure.

Unless

causedbyone

of

the

above

simple

causes,

this

errorisusually

unrecoverable.

22:

READ

ERROR

(data

block

not

present)

The

disk

controller

has

been

requested

to

readorverifyadata

block

that

was

not

properly

written.

Occursinconjunction

with

Block

commands

and

indicates

an

illegal

track

and/or

sector

request.

23:

READ

ERROR

(checksum

errorindata

block)

Thereisan

errorinthe

data.

The

sector

has

been

read

into

disk

memory,

but

its

checksumiswrong.

May

indicate

grounding

problems.

This

fairly

minor

error

is

often

repairable

by

simply

reading

and

rewriting

the

sector

with

direct

access

commands.

83

24:

READ

ERROR

(byte

decoding

error)

The

dataorheader

has

been

read

into

disk

memory,

butahardware

error

has

been

createdbyan

invalid

bit

patterninthe

data

byte.

May

indicate

grounding

problems.

25:

WRITE

ERROR

(write-verify

error)

The

controller

has

detected

a

mismatch

between

the

data

writtentodiskette

and

the

same

dataindisk

memory.

May

mean

the

diskette

is

faulty.Ifso,

try

another.

Use

only

high

quality

diskettes

from

reputable

makers.

26:

WRITE

PROTECT

ON

The

controller

has-been

requested

to

writeadata

block

while

the

write

protect

sensoriscovered.

Usually

causedbywritingtoa

diskette

whose

write

protect

notch

is

covered

over

with

tapetoprevent

changing

the

diskette's

contents.

27:

READ

ERROR

(checksum

errorinheader)

The

controller

detectedanerrorinthe

header

bytesofthe

requested

data

block.

The

block

was

not

read

into

disk

memory.

May

indicate

grounding

problems.

Usually

unrecoverable.

28:

WRITE

ERROR

(long

data

block)

The

controller

attemptstodetect

the

sync

markofthe

after

writing

a

data

block.Ifthe

sync

mark

does

not

appearontime,

this

error

message

is

generated.

Itiscausedbya

bad

diskette

format

(the

data

extends

into

the

failure.

29:

DISKIDMISMATCH

The

disk

controller

has

been

requestedtoaccessadiskette

which

has

not

been

initialized.

Can

also

occurifa

diskette

hasabad

header.

30:

SYNTAX

ERROR

(general

syntax)

The

DOS

cannot

interpret

the

command

senttothe

command

channel.

Typically,

thisiscausedbyan

illegal

numberoffile

names,oran

illegal

pattern.

Check

your

typing

and

try

again.

31:

SYNTAX

ERROR

(invalid

command)

The

DOS

does

not

recognize

the

command.Itmust

begin

with

the

first

character

sent.

Check

your

typing

and

try

again.

32:

SYNTAX

ERROR

(invalid

command)

The

command

sentislonger

than58characters.

Use

abbreviated

disk

commands.

33:

SYNTAX

ERROR

(invalid

file

name)

Pattern

matching

characters

cannotbeusedinthe

Save

commandorwhen

Opening

files

for

the

purposeofWriting

new

data.

Spell

out

the

file

name.

34:

SYNTAX

ERROR

(no

file

given)

The

file

name

was

left

out

ofacommand

or

the

DOS

does

not

recognize

it

as

such.

Typically,

a

colon

(:)

has

been

omitted.

Try

again.

84

39:

SYNTAX

ERROR

(invalid

command)

The

DOS

does

not

recognize

a

command

senttothe

command

channel

(secondary

address

15).

Check

your

typing

and

try

again.

50:

RECORD

NOT

PRESENT

The

requested

record

number

has

not

been

created

yet.

Thisisnotanerrorina

new

relative

fileorone

thatisbeing

intentionally

expanded.

It

results

from

reading

past

the

last

existing

record,orpositioning

toanon-existent

record

number

with

the

Record#

command.

51:

OVERFLOWINRECORD

The

datatobe

writteninthe

current

record

exceeds

the

record

size.

The

excess

has

been

truncated

(cut

off).Besuretoinclude

all

special

characters

(suchascarriage

returns)incalculating

record

sizes.

52:

FILE

TOO

LARGE

There

isn't

room

leftonthe

diskettetocreate

the

requested

relative

record.

To

avoid

this

error,

create

the

last

record

number

that

willbeneededasyou

first

create

the

file.Ifthe

fileisunavoidably

too

large

for

the

diskette,

either

splititinto

two

filesontwo

diskettes,

or

use

abbreviations

in

the

data

to

allow

shorter

records.

60:

WRITE

FILE

OPEN

A

write

file

that

has

not

been

closedisbeing

re-opened

for

reading.

This

file

must

be

immediately

rescued,asdescribed

in

Housekeeping

Hint#2in

Chapter4,or

it

will

becomeasplat

(improperly

closed)

file

and

probablybelost.

61:

FILE

NOT

OPEN

A

fileisbeing

accessed

that

has

not

been

openedbythe

DOS.Insome

such

casesnoerror

messageisgenerated.

Rather

the

requestissimply

ignored.

62:

FILE

NOT

FOUND

The

requested

file

does

not

existonthe

indicated

drive.

Check

your

spelling

and

try

again.

63:

FILE

EXISTS

A

file

with

the

same

nameashas

been

requested

foranew

file

already

existsonthe

diskette.

Duplicate

file

names

are

not

allowed.

Select

another

name.

64:

FILE

TYPE

MISMATCH

The

requested

file

accessisnot

possible

using

filesofthe

type

named.

Reread

the

chapter

covering

that

file

type.

65:

NO

BLOCK

Occursinconjunction

with

B-A.

The

sector

you

triedtoallocateisalready

allocated.

The

track

and

sector

numbers

returned

are

the

next higher

track

and

sector

available.

If

the

track

number

returnediszero

(0),

all

remaining

sectors

are

full.Ifthe

diskette

is

not

full

yet,

tryalower

track

and

sector.

85

66:

ILLEGAL

TRACK

AND

SECTOR

The

DOS

has

attempted

to

accessatrackorsector

which

does

not

exist.

May

indicate

a

faulty

link

pointerina

data

block.

67:

ILLEGAL

SYSTEMTOR

S

This

special

error

message

indicates

an

illegal

system

trackorblock.

70:

NO

CHANNEL

(available)

The

requested

channelisnot

available,

or

all

channels

areinuse.Amaximum

of

three

sequential

filesorone

relative

file

plus

one

sequential

file

maybeopened

at

one

time,

plus

the

command

channel.Donot

omit

the

drive

numberina

sequential

Open

command,oronly

two

sequential

files

canbeused.

Close

all

filesassoon

as

younolonger

need

them.

71:

DIRECTORY

ERROR

The

BAM

(Block

Availability

Map)onthe

diskette

does

not

match

the

copyindisk

memory.Tocorrect,

Initialize

the

diskette.

72:

DISK

FULL

Either

the

diskette

or

its

directory

is

full.

DISK

FULLissent

when2blocks

are

still

available,

allowing

the

current

filetobe

closed.Ifyou

get

this

message

and

the

directory

shows

any

blocks

left,

you

have

too

many

separate

filesinyour

directory,

and

will

needtocombine

some,

delete

any

that

arenolonger

needed,orcopy

some

to

another

diskette.

73:

DOS

MISMATCH

(CBM

DOS

V2.6

1541)

If

the

disk

error

statusischecked

when

the

driveisfirst

turned

on,

before a

directory

or

other

command

has

been

given,

this

message

will

appear.Inthat

use,

it

is

notanerror,

but

ratheraneasy

waytosee

which

versionofDOSisin

use.Ifthe

message

appearsatother

times,anattempt

has

been

madetowritetoa

diskette

with

an

incompatible

format,

suchasthe

former

DOS1on

the

Commodore

2040

disk

drive.

Use

oneofthe

copy

programsonthe

Test/Demo

diskette

to

copy

the

desired

file(s)

toa1541

diskette.

74:

DRIVE

NOT

READY

An

attempt

has

been

madetoaccess

the

1541

single

disk

withoutaformatted

diskette

in

place.

Blank

diskettes

cannotbeused

until

they

have

been

formatted.

86

PENDIX

C:

DISKETTE

FORMATS

NOTE

Nottoscale

snt

■til

iuiii

lUtl

ii

•ueii

neti

iirai

hiiii

him

Wllll

ii

cuutni

limit

ii

cuutni

huh

i

w

ITTI

10?

ITTI

ItltU

Itf

tm

uu

un

•IKl

ii

HI

un

imtunIlltt

toe

ini

toe

ini

intiucni

ur

1541

Format:

Expanded

Viewofa

Single

Sector

87

1541

BLOCK

DISTRIBUTIONBYTRACK

Track

number

1to17

18to24

25to30

31to35

RangeofSectors

0to20

0tol8

Oto

17

0tol6

Total#of

Sectors

21

19

18

17

1541

BAM

FORMAT

Track

18,

Sector

0.

BYTE

0,1

2

3

4-143

CONTENTS

18,01

65

0

DEFINITION

Track

and

sectoroffirst

directory

block.

ASCII

character

A

indicating

1541/4040

format.

Null

flag

for

future

DOS

use.

Bit

mapofthe

available

blocksintracks

1-35.

1=available

block

0=block

not

available

(each

bit

represents

one

block)

1541

DIRECTORY

HEADER

Track

18,

Sector

0.

BYTE

144-159

160-161

162-163

164

165-166

167-170

170-255

CONTENTS

160

50,65

160

0

DEFINITION

Diskette

name

padded

with

shifted

spaces.

Shifted

spaces.

Diskette

ID.

Shifted

space

ASCII

representation

of

2A,

which

are,

respectively,

the

DOS

version

(2)

and

format

type

(1541/4040).

Shifted

spaces.

Nulls

($00),

not

used.

88

PROGRAM

FILE

FORMAT

BYTE

DEFINITION

FIRST

SECTOR

0,1

Track

and

sectorofnext

blockinprogram

file.

2,3

Load

addressofthe

program

4-255

bytesofprogram

information

storedasin

computer

memory

(with

key

words

tokenized).

REMAINING

FULL

SECTORS

0,1

Track

and

sectorofnext

blockinprogram

file.

2-255

bytesofprogram

info

storedasin

computer

memory

(with

key

words

tokenized).

FINAL

SECTOR

0,1

Null

($00),

followedbynumberofvalid

data

bytesinsector.

2-???

Last

bytesofthe

program

information,

storedasin

computer

memory

(with

key

words

tokenized).

The

endofa

Basic

file

is

markedby3

zero

bytesina

row.

Any

remaining

bytesinthe

sector

are

garbage,

and

maybeignored.

SEQUENTIAL

FILE

FORMAT

BYTE

DEFINITION

ALL

BUT

FINAL

SECTOR

0-1

Track

and

sectorofnext

sequential

data

block.

2-255

254

bytesofdata.

FINAL

SECTOR

0,1

Null

($00),

followedbynumberofvalid

data

bytesinsector.

2-???

Last

bytesofdata.

Any

remaining

bytes

are

garbage

and

maybeignored.

89

1541

RELATIVE

FILE

FORMAT

BYTE

DEFINITION

DATA

BLOCK

0,1

2-255

Track

and

sectorofnext

data

block.

254

bytesofdata.

Empty

records

contain

$FF

(all

binary

ones)inthe

first

byte

followedby$00

(binary

all

zeros)tothe

endofthe

record.

Partially

filled

records

are

padded

with

nulls

($00).

SIDE

SECTOR

BLOCK

0-1

2

3

4-5

6-7

8-9

10-11

12-13

14-15

16-255

Track

and

sectorofnext

side

sector

block.

Side

sector

number

(0-5)

Record

length

Track

and

sectoroffirst

side

sector

(number

0)

Track

and

sectorofsecond

side

sector

(number

1)

Track

and

sectorofthird

side

sector

(number

2)

Track

and

sectoroffourth

side

sector

(number

3)

Track

and

sectoroffifth

side

sector

(number

4)

Track

and

sectorofsixth

side

sector

(number

5)

Track

and

sector

pointersto120

data

blocks.

90

1541

DIRECTORY

FILE

FORMAT

Track

18,

Sector

1.

BYTE

0,1

2-31

34-63

66-95

98-127

130-159

162-191

194-223

226-255

DEFINITION

Track

and

sectorofnext

directory

block.

File

entry

1*

File

entry

2*

File

entry

3*

File

entry

4*

File

entry

5*

File

entry

6*

File

entry

7*

File

entry

8*

♦STRUCTUREOFEACH

INDIVIDUAL

DIRECTORY

ENTRY

BYTE

0

1-2

3-18

19-20

21

22-25

26-27

28-29

CONTENTS

128

+

type

•

DEFINITION

File

type

OR'ed

with

$80toindicate

properly

closed

file.

(if

OR'ed

with

SCO

instead,

fileislocked.)

TYPES:0=

DELeted

1=SEQuential

2=PROGram

3=USER

4=RELative

Track

and

sectoroffirst

data

block.

File

name

padded

with

shifted

spaces.

Relative

file

only:

track

and

sectoroffirst

side

sector

block.

Relative

file

only:

Record

length.

Unused.

Track

and

sectorofreplacement

file

during

an

©SAVEor©OPEN.

Numberofblocksinfile:

storedasa

two-byte

integer,

in

low

byte,

high

byte

order.

91

APPENDIX

D:

DISK

COMMAND

QUICK

REFERENCE

CHART

General Format:

OPEN

15,8,15:PRINT#15,command:CLOSE

15

(Basic

2)

HOUSEKEEPING

COMMANDS

BASIC

2

BASIC

3.5

BOTH

NEW

COPY

RENAME

SCRATCH

INITIALIZE

VALIDATE

NEW

COPY

RENAME

SCRATCH

VALIDATE

INITIALIZE

FILE

COMMANDS

BASIC

2

BASIC

3.5

BOTH

LOAD

SAVE

LOAD

SAVE

CLOSE

GET#

INPUT#

OPEN

PRINT#

RECORD#

"NO:diskette

name,id"

"C0:new

file=0:old

file"

"R0:new

name=old

name"

"S0:file

name"

"10"

"VO"

HEADER*diskette

name,"

lid,DO

COPY

"old

file"TO"new

file"

RENAME

"old

name"TO"new

name"

SCRATCH

"file

name"

COLLECT

"10"

LOAD

"file

name",8

SAVE"0:filename",8

DLOAD

"file

name"

DSAVE

"file

name"

CLOSE

file

#

GET#file

#,variable

list

INPUT#file

#,variable

list

OPEN

file

#,8,channel

#,"0:file

name,file

type,direction"

PRINT#file

#,data

list

"P"+CHR$(channel

#)+CHR$(<record

#)

+

CHR$(>record

#)+CHR$(offset)

DIRECT

ACCESS

COMMANDS

BLOCK-ALLOCATE

BLOCK-EXECUTE

BLOCK-FREE

BUFFER-POINTER

BLOCK-READ

BLOCK-WRITE

MEMORY-EXECUTE

MEMORY-READ

MEMORY-WRITE

USER

"B-A";O;track

#;sector

#

"B-E";channel

#;O;track

#;sector

#

"B-F";O;track

#;sector

#

"B-P";channel

#;byte

"Ul";channel

#;O;track

#;sector

#

"U2";channel

#;O;track

#;sector

#

"M-E"CHR$(<address)CHR$(>address)

"M-R"CHR$(<address)CHR$(>address)CHR$(#

of

bytes)

"M-W"CHR$(<address)CHR$(>address)CHR$(#

of

bytes)

CHR$

(data

byte)

"Ucharacter"

92

Commodore 1541-II User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual