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CHARACTER SET CONVERTER
David Richard Kiarsis
Date: June 30,1973
Updated July 1982
By Peter J.Plourd II
CHANGE -- Character set converter Page 0
CHANGE is a program to aid in the conversion of
character sets foreign to the DECsystem-10. It is capable
of using any i/o device on the DECsystem-10, but is mainly
designed for users with magnetic tapes and disks. CHANGE
will perform blocking, duplication, character set
conversion, unblocking, and reading and writing of tape
1.0 RUNNING CHANGE
CHANGE may be run by typing the following:
CHANGE will respond with the date and time of day. An angle
bracket indicates that CHANGE is ready for user input.
1.1 COMMAND SYNTAX
CHANGE uses the traditional DECsystem-10 command string
format. It will accept one input file specification and one
output file specification separated by a back arrow (_) or
equal sign (=), Example:
Each output or input file specification consists of a
device, file name, extension, and project-programmer number.
The device is terminated by a colon (:), the file name by a
period (.), and the project-programmer number is enclosed in
square brackets (). Example:
The complete file specification is optional and will take on
default values if any part of it is omitted. For example,
the device will default to generic disk (dsk:), the input
file name to INPUT, the output file name to OUTPUT, the
extensions to DAT, and the project-programmer numbers to the
current disk area.
1.1.2 SWITCH SPECIFICATIONS
CHANGE -- Character set converter Page 1
In addition to the file specification each input or
output file specification includes switches. Switches are
descriptive in nature, and allow CHANGE to determine more
about the files being handled. A switch begins with a slash
and terminates on the next slash, if the switch takes no
argument, or on a colon if the switch takes an argument.
Note: the return and altmode also terminated switches as
well as the input line. Example:
If a switch takes an argument the argument follows the colon
as in the second example above. In all cases switches may
be abbreviated to the number of characters that will allow
that switch to be unique.
The following is a list of switches that CHANGE will
accept. In the following descriptions "x" represents a
decimal number, and "arg" represents a key word that may be
Designates that CHANGE should set up x buffers for the
device. This switch is used to speed up the i/o process at
the expense of core. The size of a buffer is calculated by
the following formula:
BUFSIZ = (RECORD SIZE*BLOCKING FACTOR)/BYTES PER WORD+1
Designates that CHANGE should advance x EOF marks
before processing a file. This switch has meaning only for
magnetic tapes and is ignored for all other devices. Note
that if a magnetic tape has labels, there may be several EOF
marks per file, depending on the label type.
This switch is the opposite of the advance switch. It
tells CHANGE to backspace the magnetic tape x EOF marks and
then forward space one EOF mark if the tape is not at load
point. This switch is only used with magnetic tapes and is
ignored for other devices. CHANGE resolves BACKSPACE and
CHANGE -- Character set converter Page 2
ADVANCE for the same device by subtracting the BACKSPACE
counter from the ADVANCE counter; if the result is positive
CHANGE moves the tape forward, if negative, CHANGE moves
that tape backwards. /BLOCK:x /BLKSIZE:x
This switch tells CHANGE that there are x logical
records in a logical block. For variable ebcdic, this is
the maximum number of records in the block. Note IBM's
blocking factor is the total number of characters in the
This switch tells CHANGE that there are x characters in
a logical record.
This switch is use to set the density on magnetic tapes
and is ignored for other devices. The argument is one of
the following: 200, 556, 800.
This switch saves the current command string for later
editing. See the RETAIN command for a complete description
of the RETAIN function.
For this switch CHANGE performs a RETAIN command and
then executes the current command string. See the RUN
command for a complete description.
CHANGE prints a list of its commands and switches with
a short explanation of their function. If the argument is
present, CHANGE will attempt to print the help file for that
The LABEL switch informs CHANGE that a magnetic tape
has labels or that labels should be written. In any case
the argument specifies the type of label as follows:
NONE The magnetic tape has no labels.
CHANGE -- Character set converter Page 3
MINE The magnetic tape has special
DIGITAL The magnetic tape has DECsystem-10
BURROUGHS The magnetic tape has standard
IBM The magnetic tape has IBM 360
GE635 The magnetic tape has GENERAL
ELECTRIC 635 labels.
Labels are written in the character set specified except for
IBM and GE635 labels. IBM labels are written in BCD for
7-track drives and EBCDIC for 9-track drives. GE635 labels
are always written in GEBCD.
SPECIFIES THE CHARACTER SET MODE FOR THE FILE AS
ASCII File character set is 7-bit ascii.
HPASCII File character set is 8-bit ascii.
GEASCII File character set is 9-bit ascii.
IMAGE File is read and written as 36-bit
SIXBIT File character set is sixbit with
FIXSIX File character set is sixbit with no
BCL File character set is bcl.
BCD File character set is bcd.
GEBCD File character set is GENERAL ELECTRIC
HONBCD File character set is HONEYWELL bcd.
EBCDIC File character set is ebcdic.
VEBCDIC File character set is variable ebcdic.
The end of the input record is determined by the mode of the
input file as described below:
ASCII Terminated by a carriage-return
character or record count.
SIXBIT Determined by the header word in front
FIXSIX Always copies the number of bytes
specified by the record size.
BCL Always copies the number of bytes
specified by the record size.
BCD Always copies the number of bytes
specified by the record size.
EBCDIC [fixed] Always copies the number of
bytes specified by the record size.
CHANGE -- Character set converter Page 4
EBCDIC [variable] Determined by the header
word in front of each record.
Sets the parity of a magnetic tape file, ignored for
other devices. The argument is either ODD or EVEN. The
default parity is ODD.
Sets the password for GE635 labels to the argument.
The argument can be up to twelve characters. This argument
is never checked it is only written in the output label as
Sets the reel serial number in labels that have this
feature. Note for some labels the reel serial number is
retained when writing over a label. For instance, for
BURROUGHS labels the output tape is read to retrieve the
serial number and then a new label is written with this
number. To override this feature the REEL switch is given
and the output tape is not read first (i.e. the output
label is purged).
This switch initializes the magnetic tape for industry
compatible mode. Usually set for EBCDIC and HPASCII modes.
In this mode 32-bit words are read or written. The 32-bit
word is broken down into four eight bit bytes and written in
four frames on the tape. The low-order 4-bits are not used.
Note this mode is only used for 9-track drives and will
cause unexpected results on 7-track drives.
On labeled tapes, this switch forces CHANGE to skip
down the tape, in a forward direction, until the input file
name is found or an end of tape condition is detected. This
switch is used only for labeled magnetic tapes.
CHANGE -- Character set converter Page 5
Specifies that CHANGE should abort the current job on
either an input or output parity error.
Specifies that records are allowed to cross logical
block boundaries. The normal case is that a record always
will terminate on a logical block boundary even if a partial
word will be wasted.
Specifies that the magnetic tape should be rewound.
This switch is only used for magnetic tapes and is ignored
for other devices. The arguments are as follows:
BEFORE Rewind before the operation.
AFTER Rewind after the operation.
ALWAYS Rewind always [default].
OMIT Rewind neither before or after.
Specifies that the magnetic tape should be unloaded
after the operation is completed.
Specifies that CHANGE, during a wild card search,
should type out the file names as they are found [default].
Tells CHANGE to perform a list of the devices's
directory. This switch is valid for disk, DECtape, and
magnetic tapes. Note this switch will alter a retained
command and will transfer no data.
Specifies that headers should be printed if the output
device is a line printer [default].
CHANGE -- Character set converter Page 6
Specifies that carriage-return line-feed sequences are
included in ASCII, HPASCII, and GEASCII files.
Switches flagged with an asterisk (*) can be turned off
or have the opposite effect noted, by concatenating NO with
the switch. Example:
1.1.4 EXTENDED COMMANDS
The DATA command specifies a file name that CHANGE
should use to find the conversion tables that it needs.
Note this command is ignored if a RETAIN command is in
effect. Example of use:
The data command has only been tested with disk as the
The EXIT command informs CHANGE that the user wants to
return to monitor level. CHANGE upon receiving this command
will reset all I/O and return to the monitor.
The BYE command is similar to the EXIT command except
that CHANGE will logout the user off the system instead of
returning the user to monitor level. This command is
equivalent to typing the following:
EXIT typed to CHANGE
KJOB/F typed to the monitor
2.1 SPECIAL COMMAND MODES
CHANGE -- Character set converter Page 7
This command is used to save subsequent commands typed
to CHANGE. In this mode the commands are not immediately
executed. Instead, CHANGE saves the command line and allows
the user to edit it. To edit the current command string,
once RETAIN has been typed, the user need only retype the
part of the command he wishes to change. Items that follow
the back arrow or equal sign will be edited to the input
side of the command while things that precede the back arrow
or equal sign will be edited to the output side of the
Once a command is retained the user may delete it from
memory by typing ERASE. CHANGE will erase the current
command and return to its immediate mode of interpretation;
that is CHANGE will now execute commands as they are typed.
The print command is used to examine a retained
command. As the user is editing the current command it is
useful to print it out to see if the edits are correct. To
do so the user types PRINT and CHANGE will display the
current command string
To have CHANGE perform a retained command the user
types RUN. CHANGE will then execute the current command as
if the user had typed it directly to CHANGE. If the user
finds that the command is incorrect he may stop CHANGE by
typing a control/c. CHANGE will return to command level to
accept another command. Note a retained command is never
forgotten until the user types ERASE.
The DIALOG command allows the user to carry on a dialog
with CHANGE. CHANGE will ask the user questions about the
input file specification and the output file specification.
When CHANGE feels that it has enough information it will
execute the command it has compiled. Note the command is
not retained in this mode and any command that was retained
is erased. The DIALOG mode may also be entered by typing
only an altmode to CHANGE.
3.0 TAPE FORMATS
CHANGE -- Character set converter Page 8
There are great number of different tape formats,
however, there are some rules to use when handling tapes
from certain vendors. IBM tapes, that are recorded on
9-track drives, usually use EBCDIC as the character set.
9-track IBM EBCDIC tapes always use industry compatible
mode. That is, they always write 32-bit words on the tape
in four frames. Another tape format that uses industry
compatible mode is HPASCII. In addition, data written in
this mode usually does not have return-line-feed sequences
in the text. In other character sets, trial and error must
be used to determine whether the tape is written in industry
Although some computers have the capability to write
words shorter than 36-bits (or 32-bits in industry mode),
the DECsystem-10 can only read and write 36-bit words. This
creates a problem for tapes written on the DECsystem-10 and
read on another vendors machine. Note that the reverse is
not true. CHANGE is written to handle short words if the
record size and block factor are accurate. Note this can be
determined by a trial and error procedure. If records seem
to be cut short try a larger record size, or if records seem
to be completely missed try a bigger blocking factor. In
any case, tapes written with CHANGE on the DECsystem-10, and
read on another computer may find extra characters in the
record. There is no way around this, unless the program
that reads the tape on the other computer is smart enough to
handle this condition.
4.0 TAPE DATA STRUCTURES
Definition of terms:
The smallest unit of data that can be processed by
CHANGE. In CHANGE this is also called a record.
The smallest unit of data that can be processed by the
hardware (e.g. 128 words for disk, 80 columns for the
card-reader, the data between record gaps for magnetic
An area of core memory into which the monitor reads, or
from which the monitor writes, a physical record.
CHANGE -- Character set converter Page 9
The number in the "/BLOCK:x" switch. If there is no
blocking switch the blocking factor is said to be zero.
Those buffers required to contain a number of
contiguous records, that number being the blocking factor.
A logical block may extend over many buffers, but always
uses an integral number of buffers; any unused portion of
the last buffer is wasted. If the smallest record of a file
is much smaller than the largest record, there could be
several wasted buffers, since the number of buffers required
is always determined by the size of the largest record
multiplied by the number of logical records contained in the
An ordered collection of contiguous logical records;
the largest unit of data that can be processed by CHANGE.
A file is considered blocked if the blocking factor is
non-zero; it is considered unblocked if the blocking factor
is zero or if the SPAN switch is specified.
ASCII GEASCII HPASCII
An ascii record is a set of contiguous characters
terminated by a return-line-feed sequence. Word boundaries
have no significance, and the last character of the record
is immediately followed by the first character of the next
record. The amount of buffer space required is the number
of characters in the record plus two (cr-lf). A record
terminates with the first EOL character or a satisfied
character count. If the record count was satisfied before
the EOL character was detected, the next record starts with
the next character. If the EOL character comes before the
record count is satisfied then the record terminates with no
space fill. Ascii null characters are always discarded.
HONBCD BCL BCD GEBCD FIXSIX EBCDIC
These modes are a contiguous set of characters that
terminate only on a record count. They are similar to ascii
in that they are independent of word boundaries (e.g. when
a record ends the next starts in the next character
CHANGE -- Character set converter Page 10
position). If a record ends before the count has expired
the record is space filled to the character count. In no
case will the size of the record written be unequal to the
record size. The buffer space required is the number of
characters in the record.
A sixbit record is a set of contiguous words. The
first word has, in the right half, the number of characters
in the record. The last word may be padded to ensure that
the record boundary coincides with a word boundary. The
amount of buffer space required is the number of characters
in the record plus six characters for the character count in
the first word plus the number of padding characters.
An ebcdic record is a contiguous set of characters.
The first word of a logical block contains a block control
word in the first two bytes, and spaces in the next two
bytes. This block control word contains the number of bytes
in the block. The first word of each record is the record
control word. The record count is stored in the first two
bytes and spaces in the second two. The record then
follows. Unlike sixbit, the ebcdic block and record control
words include the size of the control words. The buffer
space require is the number of characters in the record plus
four for the record control word, and plus four for the
block control word.
Only magnetic tapes have labels written out with the
data. A mag-tape file may have 2 or more labels. If the
labeled file is a multi-reel-file, it has 2 labels for each
reel. A labeled file contained entirely on one reel has
only two labels. The beginning file label occupies the
first block on the tape, and is followed by an EOF mark.
(if DIGITAL labels are used this tape mark is omitted.) The
data follows this tape mark and is terminated with another
EOF mark. The ending file label occupies the last block of
the file and is followed by another EOF mark.
5.0 CONVERSION TABLES
CHANGE does not keep all of its conversion tables in
core. It reads a data file, after the user has specified
the input and output character set, to retrieve its
CHANGE -- Character set converter Page 11
conversion tables. CHANGE will try to open a file called
"SYS:CHANGE.DAT" and if that fails it will try
"DSK:CHANGE.DAT". If both of these attempts fail CHANGE
will type out an error message an do no more. The user can
alternately tell CHANGE the name of the data file to use.
To do this the user must first erase any retained command
through the use of the "ERASE" command. Then he may use the
"DATA" command to specify the file where CHANGE is to find
the conversion tables. Note the format of the conversion
tables is defined in CHANGE at assembly time and is not
taken from the data file.
The conversion tables are really two tables in one.
That is, each table has one table in the left half of the
word and one in the right half. The left half table is the
table that converts to ascii, while the right half table
converts to the output character set. Note this means that
CHANGE internally converts all character sets to ascii.
Because CHANGE does this, character sets with more than 128
characters (such as EBCDIC) cannot be fully handled, and
some characters may be translated incorrectly. The manner
that CHANGE accesses these tables is as follows. First
CHANGE reads from the input file and extracts a byte of the
proper size. It then takes this byte and indexes by it into
the input conversion table. From the left half of the input
conversion table CHANGE extracts an ascii character
equivalent to the input character. Then with the ascii
character CHANGE indexes into the output conversion table
and extracts a character from the right half table. This
character is then the converted character and is passed to
the output file. Note if a character can not be translated
CHANGE places a back slash (\) in that position of the
There is a program called TABLE which generates the
conversion file for CHANGE. TABLE contains all of the
conversion tables which are mapped in CHANGE with IOWD
pointers. Thus to modify a table, the user need only to
modify the program TABLE. To do this, TABLE must be edited,
reassembled, and then run again.
The following are examples of commands to CHANGE:
A user has a magnetic-tape that was written on an IBM
360 system. He knows that the tape is a 9-track tape
written in IBM fixed ebcdic and wants to convert it to
sixbit for a COBOL program he is working on. In addition,
the user knows that the input tape is blocked 1 and has 80
character records. He wants the output to be blocked 20 and
CHANGE -- Character set converter Page 12
have 120 character records. To solve this problem the user
types the following command to CHANGE:
In the above example only user input was shown. He first
retained the following commands and then typed in his
command string. Once having typed in the command string the
user had CHANGE type it back to him. Having decided all was
o.k. the user had CHANGE do the command by typing "RUN" to
CHANGE. The complete output may look as follows:
CHANGE here at 12:21 02/02/73
CHANGE 12:25 02/02/73
12.021 secs. 1234 i/o units.
17777 octal locations used.
400 rec. 400 blk. read.
400 rec. 20 blk. written.
Another user has a sixbit file that his COBOL program
just generated. He wants to convert it to ascii so that he
may edited it. To do this he types the following command to
CHANGE -- Character set converter Page 13
Note in this example the input record size did not need to
be specified because CHANGE will determine it from the data.
In general if the device has a fixed buffer size and the
character set has control words or other control features
than the record size may be omitted.
CHANGE -- Character set converter Page 14
COMMAND SYNTAX . . . . . . . . 0
CONVERSION TABLES . . . . . . 10
EXAMPLES . . . . . . . . . . . 11
EXTENDED COMMANDS . . . . . . 6
SPECIAL COMMAND MODES . . . . 6
SWITCH SPECIFICATIONS . . . . 0
SWITCHES . . . . . . . . . . . 1
TAPE DATA STRUCTURES . . . . . 8
TAPE FORMATS . . . . . . . . . 7