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 and is believed to be entirely reliable.
No responsibility, however, is assumed 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 of a disk drive 1
Features of the 1541 1
How to use this book 2
Basic Operating Steps 2
Specifications of the 1541 Disk Drive 4
PART ONE: GUIDE TO OPERATION
Chapter 1: Disk Drive 5
Unpacking . 5
Empty the drive 6
Connecting the cables 6
Turning on the power 7
Troubleshooting guide 9
Simple maintenance tips 11
Chapter 2: Diskettes . 12
What is a diskette? 12
Safety rules for diskette care 13
Inserting a diskette 13
Safety rules for removing diskettes 14
Loading a packaged program 14
How to prepare a new diskette 15
Reusing an old diskette 16
Organizing a diskette library 17
Backups 17
Chapter 3: Directories 18
What is a directory? .... 18
Viewing a directory 18
What a directory shows 18
Watch out for splat files 20
Printing a directory 21
Reading a directory as a file 21
Another way to be selective 21
Pattern matching and wild cards 22

PART TWO: GUIDE TO ADVANCED OPERATION AND PROGRAMMING
Chapter 4: 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 concept of files 42
Opening a sequential file 42
Adding to a sequential file 45
Writing file data: Print# 46
Closing a file 48
Reading file data using INPUT# 49
More about INPUT (advanced) 50
Numeric Data Storage on Diskette 51
Reading File Data: Using GET# ,... 52
Demonstration of Sequential Files 54
Chapter 6: Relative Data Files 55
The value of relative 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
Expanding a relative file 60
Writing
relative file data 61
Designing a relative record 61
Writing the record 62
Reading a relative record 63
The value of index files 64

Chapter 7: Direct Access Commands 65
A tool for advanced users ... 65
Diskette organization 65
Opening a data 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
List of Figures
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
ity of your Commodore computer. As you use the 1541 disk drive, you will appreciate its
superiority to the cassette recorder you may have used before and to disk drives offered for
other brands of computers.
The 1541-n disk drive is fully compatible with the commodore 1541 disk drive, therefore
we may often omit the "-II" suffix throughout the remainder of this manual.
THE ADVANTAGES OF A DISK DRIVE
• Speed
If you have used a cassette recorder for data storage, you probably know it can take up
to an hour just to search one long cassette tape looking for a specific program. With the
1541 disk drive, a list of all the programs on a diskette appears on your screen in
seconds. The speed of program loading is also greatly improved. It takes the 1541 only
a minute to load a large program that would take a half-hour to load from tape.
• Reliability
Reliability is another reason for choosing a disk drive. It is all too common for a cassette
user to accidentally erase a valuable program by saving a new program on top of the old
one, without realizing it. The 1541 disk drive automatically verifies everything it
records.
• Direct File Access
A third advantage of a disk drive is the ability to use relative files (discussed in Chapter
6). On a diskette, any part of a relative file can be accessed and altered separately,
without affecting the rest of the file.
Overall, using a disk drive makes for easier and more powerful computing.
FEATURES OF THE 1541
The 1541 is one of the most affordable disk drives on the market. Compared to
competitors, the 1541 has high capacity, and even higher intelligence. It is one of the most
cost-effective disk drives available. Most home and personal computers that use a disk
take at least 10K of RAM memory from the computer to hold a disk operating system
(known as a DOS.) This large program must be in memory the whole time the disk is
being used, and much of it must also be kept on every 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 on a command, it will
complete it while the computer goes on to some other task, effectively allowing you to do
two things at once.

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 can I store it on this diskette, and should I pack the disk
first? (Packing is the process of moving all the leftover work areas to the end of the
diskette's storage space.) All this is handled automatically on Commodore disk drives.
The 1541 disk drive always knows where the next program 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 over a cable and
interface known as the Commodore serial bus. It is 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 next in *'daisy chain" fash
ion. Up to 4 disk drives and 2 printers can be connected this way.
HOW TO USE THIS BOOK
This book is divided into two main parts. The first part gives you the information you
need to use the 1541 effectively, even if you know little or nothing about programming.
This part of the book tells you how to set up the system, how to prepare diskettes for use,
how to read a directory, and how to load programs. Part two of the book is for advanced
users and those who would like to become advanced users. This part provides more
advanced commands, tells about the different files the 1541 uses, and how to manage
them, as well as giving a few hints for machine language programmers.
Both beginning and advanced users will find valuable information in the appendi
ces—a quick reference list of disk commands, a list of disk error messages and what they
mean, a glossary of words used in this manual, how to use two or more disk drives at
once, and explanations of some programs on the Test/Demo diskette packed with your
1541.
Since owners of four different Commodore computers use the 1541, we have
separated several explanations into two versions, depending on which Basic your com
puter uses. If you have a VIC 20 or Commodore 64, please read the pages marked Basic
2. Those with the Commodore 16 or the Plus/4 should read pages marked Basic 3.5. For
many commands, there will be an added page or two of further 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 anxious to start using your new disk drive (
right away. In view of that, we have outlined the basic steps you need to know in
order to get started.

Once you've mastered the basic steps however, you will need to refer to the rest of
this manual in order to make full use of the 1541 *s features. In fact, before you begin, you
should take a look at the 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 turn on the disk drive.
There's no shortcut through this part. You'll have to read this section to find out
what connects to what, when to turn everything on, and how to empty the drive.
If you run into any problems at this point, refer to the Troubleshooting Guide.
Gently insert a pre-programmed diskette.
For the purpose of demonstration, use the Test/Demo diskette that was included
with the disk drive.
If you run into any problems at this point, refer to Chapter 2, "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 of a particular program on the Text/Demo diskette. To
load a different BASIC program, substitute the name of that program inside the
quotation marks.
If you want to load a program that isn't written in BASIC language, you must
use the Basic 2 command 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 "Loading a Packaged Program."
4. After you perform step 3, the following will appear on the 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.

SPECIFICATIONS OF THE 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,
and as internal timers
16116 RAM Random Access Memory
Used as 2K of buffers
1 16KROM Read-Only Memory
Contains a 16K 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 may be used (Commodore diskettes are recom
mended).

PART 1: GUIDE TO OPERATION
CHAPTER 1
DISK DRIVE
UNPACKING
The first thing you will need to do with your disk drive is unpack it. Inside the carton
in which you found this manual, there should also be: a 1541 disk drive, supply power
a black cable to connect the disk drive to the computer, a demonstration diskette, and
a warranty card to be filled out and returned to Commodore.
Please don't connect anything until you've read the next three pages! It could save
you a lot of trouble.
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, it is very important to be sure nothing is inside the disk drive. If you turn the
power off or oh with a diskette in the drive, you could lose its contents and have to re-
record it. Since you wouldn't like having to do that, always check to be sure nothing is
inside the drive before turning it off or on.
When you first unpack the disk drive, you will find a cardboard shipping spacer
inside. Following the instructions below, pull it out as though it were a diskette, but don't
throw it away. You will want to put it back inside the slot any time you move or ship the
disk drive later.
To check whether the drive is empty (Fig. 1), simply rotate the lever on the front
of the disk drive counter-clockwise until it stops, one-quarter turn at most. Then reach
inside the long slot the lever covers when it points down, and pull out any diskette you
find there.
CONNECTING THE CABLES
With the power supply, the power cable plugs into the back of the disk drive at one
end, and into a grounded (3-prong) outlet at the other end.It will only go in one way. Before
you plug it in though, make sure that your entire computer system is turned off. The disk
drive's on/off switch is in the back, on the right side (when viewed from the back). It is
off when the botton half is pushed inward. Leave your whole system off until everything
is connected. We will tell you when it is safe to turn it on.
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 and a suitable outlet, find the black
cable that goes from the disk drive to the computer. It is called a serial bus cable to
describe the way the computer, and other accessories communicate with each other
through its wires. It has an identical 6-pin DIN connector at each end, which like the
power connector can only go in one way—with the dimple in the side of the plug facing
up.
To plug in the serial bus cable, find the dimple on the side of the metal part of the
plug and turn that side up. Then push it straight into one of the two serial bus connectors
on the back of the disk drive. The other end goes into the similar connector on the back of
your computer, marked '*serial bus." If another accessory, such as a printer, is already
connected there, unplug the other device's cable from the computer, and attach it to the
spare serial bus connector on the back of the 1541. Then install the serial cable from the
1541 in the serial bus connector on the back of the 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 connector on the back of the previous disk 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, as no two disk drives can have the same device number.
We'll cover ways of changing disk device numbers in Appendix A. Until you are ready to
read that section, you may find it easier to leave your extra drive(s) unconnected.
TURNING ON THE POWER
With everything hooked up, and the disk drive empty, it is time to turn on the power.
You can turn on the power to the disk and other devices on the serial bus (connected via
serial cables) in any order you like. Just be sure to either turn on the power to the computer
itself last, or to. use a multiple outlet power box with a master switch to turn everything off
and on at once. When everything is on, including the computer, the disk drive will go
through a self check for a second or so, to be sure it is working correctly. After the drive is
satisfied with its own health, it will flash the green light once, and the red power-on light
will glow continuously. At the same time, the computer will be going through a similar
self-test, and displaying its hello message on your TV or video monitor. Once the green
light on the disk drive has flashed and gone out, it is safe to begin working with the drive.
If the light doesn't go out, but continues to flash, you may have a problem. Refer to the
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
is in the "on" position
Check both cords of power
cable to be sure they
are fully inserted
Replace fuse or reset
circuit breaker in house
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 If it repeats, try again
power-up, before with the serial bus
any disk commands disconnected. If it
have been given still repeats, call your
dealer. If unplugging
the serial cable made a
difference, check the
cable for proper
connection at both ends.
This can also be caused
by some cartridges on
the C-64 and always by
a 16K cartridge on the
VIC 20. Remove the
cartridge and power-up
the disk drive again to
determine where the
problem is.
(The principle behind unplugging the serial cable is "divide and conquer.'1 The drive can do its
power-on test even when not connected to a computer. If it succeeds that way, then the problem is
probably in the cable or the rest of the 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
give no error message.
Serial bus cable
not well connected, or
disk not turned on.
Another device on the
serial bus may be
interfering.
Be sure serial bus cable
is correctly inserted
and disk drive is turned
on
Unplug all other devices
on the serial bus. If
that cures it, plug them
in one at a time. The
one just added when the
trouble repeats is most
likely the problem.
Also, trying to load a
machine language program
into BASIC space will
cause this problem.
(Such devices may not be turned on properly, or may have conflicting device numbers. Only one
device on the 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
channel to see why the
error occurred. Follow
the advice in Appendix B
to correct it.
(Be sure to spell program names exactly right, as the disk drive is very particular, even about spaces
and punctuation marks, and will not load a program unless you call it exactly the same thing it was
called when it was saved on the diskette.)
Your own programs Load
fine, but commercial
programs and those
from other 1541 owners
fail to load.
Either the diskette you
are loading is faulty,
(some mass-produced
diskettes are) or your
disk drive is misaligned.
Try another copy of the
troublesome programs. If
several programs from
several sources always
fail to load, have your
dealer align your
disk drive.
Your own programs that
used to Load won't
any more, but programs
saved on newly-formatted
diskettes still work.
Older diskettes have
been damaged.
The disk drive has gone
out of alignment.
See the section on safety
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 years to come, but there are a few things you
can do to avoid costly maintenance.
1. Keep the drive well-ventilated. Like a refrigerator, it needs a few inches of air
circulation on all sides to work properly.
2. Use only good quality diskettes. Badly-made diskettes could cause increased wear on
the drive's read/write head. If a particular diskette is unusually noisy in use, it is probably
causing added wear, and should be replaced.
3. Avoid using programs that "thump" the drive as they load. Many commercial
programs, and diskettes that are failing, cause the disk drive to make a bumping or
chattering noise as it attempts to read a bad sector. If the diskette can be copied to a fresh
diskette, do so immediately. If it is protected by its maker against copying, the thumping
is intentional and will have to be endured. Be aware, however, that excessive thumping,
especially when the drive is hot, caused some older 1541's to go out of alignment and led
to costly repairs. Current 1541's have been redesigned to prevent the problem.
Note: the "Memory-Write" example in Chapter 8 temporarily turns off the bumps.
4. It would be a good idea to have your 1541 checked over about once a year in normal
use. Several items are likely to need attention: the felt load pad on the read/write head may
be dirty enough to need replacement, the head itself may need a bit of cleaning (with 91%
isopropyl alcohol on a 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 need to be dusted to be sure its optical sensor has a clear view. Since most of these
chores require special materials or parts, it is best to leave the work to an authorized
Commodore service center. If you wish to do the work yourself, ask your dealer to order
the 1541 maintenance guide for you (part number 990445), but be aware that home repair
of the 1541 will void your warranty.
11

CHAPTER 2
DISKETTES
WHAT IS A DISKETTE?
Before we actually begin using the drive, let's take a moment to look at the
Test/Demo diskette packed with the disk drive. To do this, grasp it by the label, which
should be sticking out of the paper jacket. Then pull it out of the jacket which keeps it free
of dust and other contaminants. (Save the jacket; the diskette should always be kept in its
jacket except when actually in use in the disk drive.) It is often called a floppy diskette,
because it is flexible, even though it is not safe to bend diskettes.
A diskette is much like a cassette tape, but in the form of a circle and enclosed within
a protective square plastic cover. As on a cassette tape, only a small exposed portion of
the magnetic recording surface is sensitive. You may touch the rest of the diskette any
time you like, but avoid touching the few small portions that are not covered by the
protective cover. Also, never try to remove this cover. Unlike the paper jacket, the plastic
diskette cover is intended to remain on permanently.
Next, notice the notch on one side of the diskette (it may be covered by a piece of
tape). This notch is called the write protect notch. When it is covered with the opaque tape
packed with blank diskettes, the disk drive cannot change the contents of that diskette.
Never remove the tape on the Test/Demo diskette.
The label on the top of the diskette says "1541 Test/Demo" on it, and tells you
which diskette you are using. Blank diskettes come with extra labels in addition to one
applied by the maker of the diskette. Use them to describe your own diskettes.
<* At least two other parts of the diskette are worth mentioning: The hub and the access
slot. The hole in the center is called the hub. A cone-shaped spindle fills it when the drive
door is closed, and its edges are clamped. This keeps them from slipping, when the
diskette spins at 300 RPM in use.
The oval opening in the diskette opposite the label is called the access slot. It exposes
just enough of the diskette's surface for the read/write head and load pad inside the drive
to touch a one inch long line from the center to the edge of the diskette's working surface.
The bottom side of that slot is where all the information is written as the 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