Commodore 1541 User manual

A Friendly Introduction to Your 1541 Disk Drive
t commodore
COMPUTER

USER'S GUIDE STATEMENT
"This equipment generates and uses radio frequency energy. If it is
not properly installed and used in strict accordance with the manufac
turer's instructions, this equipment may interfere with radio and tele
vision reception. This machine has been tested and found to comply
with the limits for a Class B computing device peripheral in accord
ance with the specifications in Subpart J of Part 15 of FCC Rules,
which are designed to provide reasonable protection against such
interference in a residential installation. If you suspect interference,
you can test this equipment by turning it off and on. If you determine
that there is interference with radio or television reception, try one
or more of the following measures to correct it:
• reorient the receiving antenna
• move the equipment away from the receiver
• change the relative positions of the equipment and the receiver
• plug the equipment into a different outlet so that the equipment
and the receiver are on different branch circuits.
If necessary, consult your Commodore dealer or an experienced radio/
television technician for additional suggestions. You may also wish to
consult the following booklet, which was prepared by the Federal
Communications Commission:
"How to Identify and Resolve Radio-TV Interference Problems".
This booklet is available from the U.S. Government Printing Office,
Washington, D.C. 20402, Stock No. 004000-00345-4.

COMMQDORI
1541
DISK DRIVE
A Friendly Introduction to Your 1541 Disk Drive
f:commodare
v COMPUTER

The information in ihis manual has been reviewed and is believed to be entirely
reliable. No responsibility, however, is assumed for inaccuracies. The material in (his
manual is for information purposes only, and is subject to change without notice.
tjyCommodore Business Machines Electronics Ltd., September 1982
"All rights reserved."

Table of Contents Pa8«
1. GENERAL DESCRIPTION •
2. UNPACKING AND CONNECTING *
Contents of Box 4
Connection of Cables '
Powering On • "
*' Insertion of Diskette 7
■ Using with VIC 20 or Commodore 64 7
3. ©SING PROGRAMS 8
Loading Pre-packaged Software 8
LOAD 8
Directory of Disk "
Pattern Matching & Wild Cards 11
SAVE IZ
SAVE and replace I2
VERIFY n
DOS Support Program 13
4. DISK COMMANDS 14
OPEN AND PRINT # «
NEW I5
COPY 16
RENAME 16
SCRATCH 17
INITIALIZE n
VALIDATE !7
DUPLICATE 18
Reading the Error Channel 18
CLOSE 19
5. SEQUENTIAL FILES 20
OPEN 20
PRINT # and INPUT # 21
GET # U
Reading Ihe Directory M
6. RANDOM FILES M
Opening a channel for random access dala 2'
BLOCK-READ 29
BLOCK-WRITE 3°
BLOCK-ALLOCATE 30
BLOCK-FREE 31
BUFFtlR-POINTER 33
USER1 and USER2 3*

7. RELATIVE FILES 36
Creating a relative file. , , 35
Using relative files , , < ^ _ -jg
Create a relative tile , , , 43
Sum man - 43
Modifying the program....... „..„ ... 44
8. PROGRAMMING THE DISK CONTROLLER 45
BLOCK-EXECUTE \[ 4S
MEMORY-REAP ' 45
MEMORY-WRITE .....«^! 46
MEMORY-EXECUTE ."!!!,"!!!!.'."!"! 46
USER Commands ti 47
9. CHANGING THE DISK DEVICE NUMBER 48
Software Method , ,„ t ,.48
Hardware Method , nmt 4«;
10. ASSEMBLY LANGUAGE AND THE 1541 50
Appendices
A. Disk Command Siunmun 51
B. Error Messages , , , 52
C. Demonstration Disk Programs , , 57
D. Disk Formate Tables , , 64

1. GENERAL DESCRIPTION
INTRODUCTION
Welcome to the fastest, easiest, and most efficient filing system available for your
Commodore 64 or VIC 20 computer, your 154] DISK DRIVE. This manual has been
designed io show you how to get the most from your drive, whether you're a beginner
or an advanced professional.
If you are a beginner, the first few chapters will help you through the basics of
disk drive installation and operation. As your skill and programming knowledge im
proves, you will find more uses for your disk drive and the more advanced chapters of
this manual will become much more valuable.
If you're a professional, this reference guide wiil show you how to put the 1541
through its paces Id perform just about all the disk drive jobs you can think of.
No matter what level of expertise you haveh your 1541 disk drive will dramatically
improve the overall capabilities of your computer system.
Before you get to the details of 1541 operation, you should be aware of a few im
portant points. This manual is a REFERENCE GUIDE, which means that unless the
information you seek directly pertains lo the disk or disk drive you will have to use
your Commodore 64 or VIC 20 User's Guides and Programmer's Reference Guides to
find programming information. In addition, even though we give you step-by-step in
structions for each operation, you should become familiar with BASIC and the in
structions (called commands) that help you operate your disks and drives. However, if
you just want to use your disk drive unit lo load and save prepackaged software, we've
included an easy and brief section on doing just that.
Now , . , let's get on with the general information.
The commands for the disk drive come in several levels of sophistication. Starting
in chapter three, you can learn how the command that allow you to SAVE and LOAD
programs with (he disk work. Chapter four teaches you how commands are sent to the
disk, and introduces the disk maintenance commands.
Chapter five tells you how to work with SEQuential data flies. These are very
similar to their counterparts on tape (but much faster). Chapter six introduces the com
mands that allow you to work with random filcsj lo access any piece of data on the
disk, and how you organize the diskette into tracks and blocks. Chapter seven
describes The special relative files. RELaiive Files are the best method of storing data
bases, especially when they are used along with sequential files.
Chapter eight describes methods for programming the disk controller circuits at
the machine language level. And the final chapter shows you how to change the disk
device number, by cutting a line inside the drive unit or through software.

Remember, you don't really need to learn everything in this book all at once. The
first four chapters are enough to get you going, and tne next couple are enough for
most operations. Getting ta know your disk drive will reward you in many ways —
speed of operation, reliability, and much more flexibility in your data processing
capabilities.
SPECIFICATIONS
This disk drive allows you to store up to 144 different programs and/or data files
on a single mini-floppy diskette, for a maximum of over 174,000 byics worth of infor
mation storage.
Included in the drive is circuitry for both the disk controller and a complete disk
operating system, a total of 16K of ROM and 2K of RAM memory. This circuitry
makes your Commodore 1541 disk drive an "intelligent" device. This means it does its
own processing without talcing any memory away from your Commodore 54 or VIC 20
computer. The disk uses a "pipeline" software system. The "pipeline" makes the disk
able to process commands while the computer is performing other jobs. This
dramatically improves the overall throughput (input and outpu*) of the system.
Diskettes that you create in this disk drive arc read and write compatible with
Commodore 4040 and 2031 disk drives, Therefore, diskettes can be used inter
changeably on any of these systems. In addition, this drive can read programs created
on the older Commodore 2040 drives.
The 1541 disk drive contains a dual "serial bus" interface. This bus was specially
created by Commodore. The signals of this bus resemble the parallel IEEE-488 inter
face used on Commodore PET computers, except that only one wire is used to com
municate data instead of eight. The two ports at the rear of the drive allows more than
one device to share the serial bus at the same time. This is accomplished by "daisy-
chaining" the devices together, each plugged into the next. Up to five disk drives and
one printer can share the bus simultaneously.

Figure 1.1 Specifications VIC 1540/1541 Single Drive Floppy Disk
STORAGE
Total capacity
Sequential
Relative
Directory entries
Sectors per track
Bytes per sector
Tracks
Blocks
174848
bytes per diskette
168656 bytes per diskette
167132 bytes per diskette
65535 records per file
144 per diskette
17(0 21
256
35
683 (664 blocks free)
IC\:
6502
6522 (2)
Buffer
2114(4)
PHYSICAL;
Dimensions
Height
Width
Depth
Electrical:
Power Requirements
Voltage
Frequency
Power
MEDIA:
Diskettes
microprocessor
I/O, internal timers
2K RAM
97 mm
200 mm
374 mm
100, 120, 220, or 240 VAC
50 or 60 Hertz
25 Watts
Standard mini 5V4", single sided,
single density

2. UNPACKING AND CONNECTING
CONTENTS OF BOX
Included with the 154] disk drive unii, you should find a gray power cable, black
serial bus cable, this manual, and a demonstration diskette. The power cable has a con
nection for the back of ihc disk drive on one end, and for a grounded (three-prong)
electrical outlet on the other. The serial bus cable is exactly the same on both ends. H
has a 6-pin DIN plug which attaches to the VIC 20, Commodore 64 or another disk
drive.
Please, don't hook up anything until you've completed the following section!
iFigl.A
£i commodore
1541
1
DRIVE JNDICATER (RED LED)
LIGHT: ACTIVE
FLASH: ERROR
POWER INDICATER
Fig !. Front Panel ]green LED) LIGHT: POWERQN
} Fig 13
DRIVE INDICATOR (RED LED) LIGHT: ACTIVE
FLASH ERROR
POWER JNDICATEP
(GREEN LED) LIGHT: POWER ON

Fig 2. Back Panel
POWER SWITCH
SERIAL BUS
FUSE/HOLDER
CONNECTION OF CABLES
Your first step is to take the power cable and insert it into the back of the disk
drive (see figure 2). It won't go in if you try to put it in upside down. Once it's in the
drive, plug the other end into the electrical outlet. IF the disk drive makes any sound at
this time, please turn il off using the switch on (he back! Don't plug any other cables
into Ihe disk drive if Ihe power is on.
Next, take the serial bus cable and attach il to either one of the serial bus sockets
in Ihe rear of the drive. Turn off ihe computer, and plug the other end of the cable into
the back of the computer. That's all there is to it!
If you have a printer, or any additional disk drives, attach the cables into the se
cond serial bus port (see figure 3). For directions on using multiple drives at one time,
read chapter 9. If you are a first-time user with more than one drive, start working with
only one drive until you're comfortable with the unit.
Fig 3. Floppy Disk Hookup

POWERING ON
When you have all the devices hooked together, it's time to start turning on the
power. II Is important Ihnl you turn on the devices in the correct order. The computer
should always be turned on last. As long as the computer is the last one to be turned
on, everything will be OK.
First, make sure that you've removed all diskettes from the disk drives
before powering on.
After all the other devices have been turned on, only then is it safe to turn on the
computer. All the other devices will go through their starting sequences. The printer's
motor goes on, with the print head moving halfway across the line and back again. The
1541 disk drive will have its green light on, and then the red drive/error light will blink,
while your TV screen forms the starting picture.
Once the red drive/error light has stopped flashing on the drive, it is safe to begin
working with it.
WRITE
PROTECT
NOTCH
WHEN COVERED, DISKETTE
CONTENTS CANNOT BE
ALTERED
Fig.4. Position for Diskette Insertion

INSERTION OF DISKETTE
There is different way to open and close the drive door, and insertion/
removal the diskette.
TYPE1: figure l.A ,.._,.•
To open the door on the drive, simply press the door catch lightly, anil LSie
door will pop open. If there is a diskette in ihc drive, it is ejected by a small
spring. Take the diskette to be inserted, and place it in the drive face-up with the
large opening going in first and write-protect notch to the left (covered with tape
in the demonstration disk) (sec figure 4).
Press it in gently, and when the diskette is in all the way, you will feel a click
and the diskette will not spring out. Close the drive door by pulling downward
until the latch clicks into place. Now you are ready to begin working with the
diskette.
TYPE2: figure 1,B
To open the door on the drive, simply turn the door Sever counter-clockwise.
Take the diskette to be inserted, and place it in the drive face-up with the large
opening going in first and write-protect notch to the Seft (covered with tape in
the demonstration disk) {see figure 4).
Close the drive door by turning clockwise direction unti! the latch clicks
into place. Now you are ready to begin working with the disk.
Remember to always remove the diskette before the drive is turned off or on.
Never remove the diskette when the red drive light in on! Data can be destroyed by the
drive at this time!
USING WITH A VIC 20 OR COMMODORE 64
The 1541 Disk Drive can work with either the VIC 20 or Commodore 64 com
puters. However, each computer has different requirements for speed of incoming
data. Therefore, there is a software switch for selecting which computer's speed to use.
The drive starts out ready for a Commodore 64. To switch to VIC 20 speed, the follow
ing comand must be sent after the drive is started (power-on or through software):
OPEN 15, 8. 15, -UI-": CLOSE 15
To return the disk drive to Commodore 64 speed, use this command:
OPEN 15, 8, 15, "U1+": CLOSE 15
More about using this type of command is in chapter 4, wiih a detailed explana
tion of the U (user) commands in chapter 8.

3. USING PROGRAMS
LOADING PREPACKAGED PROGRAMS
For those of you interested in using only prepackaged programs available on car
tridges, cassette, or disk, here's all you have lo do:
Using your disk drive, carefully insert the preprogrammed disk so that the label on
the disk is facing up and is closest to you. Look for a little nolch on the disk (it might
be covered with a little piece of tape). If you're inserting the disk properly, the notch
will be on the left side. Once the disk is inside, close [he protective gate by pushing in
on the level. Now type LOAD'TROGRAM NAME", 8 and hit the
The disk will make noise and your screen will say:
SEARCHING FOR PROGRAM NAME
LOADING
READY
When the word READY appears, just type RUN, and your prepaekaged software
is ready to use.
LOAD
The BASIC commands used with programs on the disk drive are the same as the
commands used on the Commodore DATASSETTE™ recorder. There are a few extra
commands available for use with disks, however.
First of all, the program name must be given with each command. On a
DATASSETTE™, you could omit the program name in order to just LOAD the first
program there. On disk, since there are many different programs thai are equally ac
cessible, the program name must be used to tell the disk drive what to do. In addition,
the disk drive's device number must be specified. If no device number is listed, the
computer assumes the program is on tape.
FORMAT FOR THE LOAD COMMAND:
LOAD nameS,device#, commands
The program name is a string, that is, either a name in quotes or the contents of a
given string variable. Some valid names are: "HELLO", "PROGRAM ffl", AS,
NAMES.
The device*/ is preset on the circuit board to be #8. If you have more than one
drive, sec chapter 9 on how to change the device number. This book assumes that
you're using device number 8 for the disk drive.

The commands is optional. If not given, or zero, the program is LOADed nor
mally, that is, beginning at the start of your available memory for BASIC programs. If
the number is 1, the program will be LOADed at exactly the same memory locations
from which it came. In the case of computers with different memory configurations,
like VICs with 5K, 8K, or more memory, the start of BASIC memory is in different
places. The command/* 0 permits BASIC programs to LOAD normally. CommandW 1
is used mainly for machine language, character sets, and other memory dependent
functions.
EXAMPLES
LOAD "TEST", 8
LOAD "Program # 1", 8
LOAD AS. J , K
LOAD "Mach Lang", 8. 1
NOTE: You can use variables to represent device numbers, commands, and
strings, as long as you've previously defined them in your program.
DIRECTORY OF DISKETTE
The DATASSETTE™ tape deck is a sequential device. It can only read from the ■
beginning of the tape to the end, without skipping around the tape and without the
capability of going backward or recording over old data.
Your disk drive is a random access device. The read/write head of the disk can go
to any spot on the disk and access a single block of data which holds up to 256 bytes of
information. There are a total of 683 blocks on a single diskette.
Fortunately, you don't really have to worry about individual blocks of data.
There is a program in the disk drive called the Disk Operating System, or the DOS.
This program keeps track of the blocks for you. It organizes them into a Block
Availability Map. or BAM, and a directory.
The Block Availability Map is simply a checklist of all 683 blocks on the disk. It is
stored in the middle of the diskette, halfway between the center hub and the outer rim.
Every time a program is SAVEd or a data Tile is CLOSEd, the BAM is updated with
the list of blocks used up.
The directory is a list of all programs and other files stored on the disk. It is
physically located right next to the BAM. There are 144 entries available in the direc
tory, consisting of information like file name and type, a list of blocks used, and the
starting block. The directory is automatically updated every time a program is SAVEd

or a file is OPENed for writing. BEWARE; the BAM isn't updated until the file is
CLOSEd, even though the directory changes right away. If a file isn't CLOSEd pro
perly, all data in thai file will probably be lost.
The directory can be LOADed into your memory just like a BASIC program.
Place the diskette in the drive, and type the following command:
LOAD "$", 8
The computer responds with:
SEARCHING FQRS
FOUND S
LOADING
READY.
Now the directory is in your computer's memory. Type LIST, and you'll see die
directory displayed on the screen. To print the directory on your printer, type the
following command line (in this example your printer is plugged in as device? 4):
OPEN 4, 4: CMD 4: LIST
NOTE: When using CMD, the Tile must be closed using the command PRINTS
4: CLOSE 4. See the VIC 1525/1515 printer manual for detailed explanation.
To read the directory without LOADing it into your memory, see the section later
in this chapter on the DOS Support Program. In addition, to examine the directory
from inside a BASIC program t see the section in chapter 5 that deals with the GET#
statement.
10

Can Be A String
Variable Or The
Name Inside Quotes
PATTERN MATCHING AND WILD CARDS
When using the tape deck, you can LOAD any program starting with certain let
ters just by leaving off any following letters. Thus, the command LOAD "T" will find
the
first program on the tape beginning with the letter T. And LOAD "HELLO" will
find the first program beginning with the letters HELLO, like "HELLO THERE.1'
When using the disk, this option is called pattern matching, and there is a special
character in the file name used to designate this. The asterisk {*) character
following any program name tells the drive you want to find any program start
ing with that name.
FORMAT FOR PATTERN MATCHING:
LOAD nameS +
In other words, if you want to LOAD the first program on Che disk starting with
the letter T, use the command LOAD "t*", 8,
If only the "• is used for the name, the lasl program accessed on the disk is the
one LOADed. If no program has yet been LOADed, the first one listed in the directory
is the one used.
You are probably familiar with the concept of wild cards in poker where one card
can replace any other card needed. On your 1541, the question mark (?) can be used as
a wild card on the disk. The program name on the disk is compared la the name in the
LOAD command, but any characters where there is a question mark in the name aren't
checked.
For instance, when the command LOAD "TINT", 8 is given, programs that
match include TINT, TENT, etc.
When LOADing the directory of the disk, pattern matching and wild cards can be
used GO check for a list of specific programs. If you gave the command LOAD
"SO:TEST", only the program TEST would appear in the directory {if present on the
disk). The command LOAD "S0:T*" would give you a directory- of all programs
beginning with the letter T. And LOAD "SOiTIST" would give you all the programs
with 4-letter names having the first letter of T and the third and fourth letters ST.
LOAD "$0:T?ST*" would give names of any length with the correct first, third, and
fourth letters.
II

SAVE
To SAVE a program to the diskette, all that is needed is to add the device number
after the program name. Just like the SAVE command for the tape deck, the device
number can be followed by a command number, to prevent the automatic re-location
on LOADing (sec the section on the LOAD command, above).
FORMAT FOR THE SAVE COMMAND:
SAVE namel, device*, command//
See the LOAD command (page 10) for an explanation of the parameters device^
and command^.
When you tell the disk drive 10 SAVE a program, the DOS must take several
steps. First, it looks at the directory to see if a program with thai name already exists.
Next it checks to see that there is a directory entry available for the name. Then it
checks [he BAM to see if there are enough blocks in which to store the program. If
everything is OK up to this point, the program is stored. If not, the error light wilJ
flash.
SAVE AND REPLACE
If a program already exists on the disk, it is often necessary to make a change and
re-SAVE it onto the disk. In this case, it would be inconvenient to have 10 erase the old
version of the program and then SAVE it.
If the first characters of the program name are the M@" sign followed by a 0 and
a colon (:), the DOS knows to replace any old program that has thai name with the
program that is now in the computer's memory, The drive checks the directory to find
the old program, then it marks thai entry as deleted, and it next creates a new entry
with the same name. Finally, the program is stored normally.
FORMAT FOR SAVE WITH REPLACE:
SAVE "@0:" + nameS, device*, command*
For example, if a file was called TEST, the SAVE and replace command would be
SAVE "@0: TEST'\8. If the name is in AS, the command is SAVE AS + "@0:
TEST", 8.
The reason for the 0: is to keep compatibility with other Commodore disk
drive units which have more than one drive built in. In that case, the number 0
or 1 is used to specify which drive is being used.

VERIFY
The VERIFY command works to check the program currently in memory against
the program on disk. You must include a device# with the VERIFY command. The
computer does a byte-by-byte comparison of the program, including line links —
which may be different for different memory configurations. For instance, if a pro
gram was SAVEd to disk from a 5K VIC 20, and re-LOADed on an 8K machine, it
wouldn't VERIFY properly because the links point to different memory locations.
FORMAT FOR VERIFY COMMAND:
VERIFY namcS, device*
DOS SUPPORT PROGRAM
On your demonstration disk, there may be a program called DOS SUPPORT.
This program, also called a wedge, allows you to use many disk commands more easily
(different wedges are used for the VIC 20 and the Commodore 64). Just LOAD the
program and RUN it. It automatically sets itseif up and erases itself when it's finished.
You'll have a few hundred less bytes to work with when this program is running, but
you'll also have a handy way to send the disk commands.
As a result of the DOS Support, the "/" key now takes the place of the LOAD
command. Just hit the slash followed by the program name, and the program is
LOADed. When you use this method, you don't need to use the LOAD command or
the comma 8.
The "@" and " > " keys are used to send commands to the disk drive. If you
type @$ (or > $), the directory- of the disk is displayed on the screen, without
LOADing into your memory! These keys also take the place of the PRINTS (see
chapter 4) to send commands listed in the next chapter.
To read the error channel of the disk (when the red error light is blinking), just hit
either the <£ or the > and hit RETURN Key. Trie complete error message is dis
played to you: message number, text, and track and block numbers.
13

4* DISK COMMANDS
OPEtV AND PRINT #
Up 'til now, you have explored the simple ways of dealing with the disk drive. In
order to communicate with the disk drive more fully, you have to touch on the OPEN
and PRINTS statements in BASIC (more details of these commands arc available in
yaur VIC 20 or Commodore 64 User's Guide or Programmer's Reference Guide). You
may be familiar with their use with data files on cassette tape, where the OPEN state-
ment creates the file and the PRINTS* statement Fills the file with data. They can be
used the same way with the disk, as you will see in the next chapter. But ihey can also
be used to set up a command channel. The command channel lets you exchange infor
mation between the computer and the disk drive.
FORMAT FOR THE OPEN STATEMENT:
OPEN filc#r device*, channel*, (cxtS
The filetf can be any number from 1 to 255. This numbe: is used throughout the
program to identify which Tile is being accessed. Bui numbers greater than 127 should
be avoided, because they cause the PRINT# statement to generaie a linefeed after the
return character. These numbers are rcaJiy meant to be used with non-standard
printers.
The device*/ of the disk is usually 8.
The channel* can be any number from 2 to 15. These refer to a channel used to
communicate with the disk, and channels numbered 0 and 1 are reserved for the
operating system to use for LOADing and SAVEing. Channels 2 through 14 can be
used for data to files, and 15 is the command channel.
The textS is a string that is PRINTed to the file, as if with a PRINTS statement.
This is handy for sending a single command to the channel,
EXAMPLES OF OPEN STATEMENTS:
OPEN 15, 8, 15
COMMAND CHANNEI
^ --_-^ ^—^—^- s
COMMANDJ(texlS)
OPEN 2, 8.2
OPEN A, B, C, Z$