Hardware Reference
In-Depth Information
Table 3.2
DOS control characters
Control
Hex.
character
code
Function
03
Terminates the current program (if possible) and returns control to the user.
<CTRL-C>
07
Sounds the audible warning device (bell) but can only be used as part
of a program of batch file.
<CTRL-G>
08
Moves the cursor back by one space (i.e. the same as the
<BACKSPACE>
key)
and deletes the character present at that position.
<CTRL-H>
09
Tabs the cursor right by a fixed number of columns (usually eight). Performs
the same function as the
<TAB>
key.
<CTRL-I>
10
Issues a line feed and carriage return, effectively moving the cursor to
the start of the next line.
<CTRL-J>
12
Issues a form feed instruction to the printer.
<CTRL-L>
13
Produces a carriage return (i.e. has the same effect as
<RETURN>
).
<CTRL-M>
16
Toggles screen output to the printer (i.e. after the first
<CTRL-P>
is issued,
all screen output will be simultaneously echoed to the printer. A subsequent
<CTRL-P>
will disable the simultaneous printing of the screen output).
Note that
<CTRL-PRT.SC.>
has the same effect as
<CTRL-P>
.
<CTRL-P>
19
Pauses screen output during execution of the
TYPE
command
(
<CTRL-NUM.LOCK>
has the same effect).
<CTRL-S>
26
Indicates the end of a file (can also be entered using
<F6>
).
<CTRL-Z>
Finally, the combination of three keys,
<CTRL-ALT-DEL>
, can be used to
perform a 'warm' system reset. This particular combination should only be
used in the last resort as it will clear system memory. Any unsaved data present
in RAM will then be lost forever!
If it is necessary to repeat or edit the previous command, the
<F1>
(or right-
arrow) key may be used to reproduce the command line, character by character,
on the screen. The left-arrow key permits backwards movement through the
command line for editing purposes.
The
<F3>
key simply repeats the last
command in its entirety.
File specifications
Many of the DOS commands make explicit reference to files. A file is simply
a collection of related information stored on a disk. Program files comprise a
series of instructions to be executed by the processor whereas data files simply
contain a collection of records. A complete file specification has four distinct
parts: a drive and directory specifier (known as a
pathname
), a
filename
, and a
filetype
.
The drive specifier is a single letter followed by a colon (e.g.
C
:). This is
then followed by the directory and sub-directory names (if applicable) and the
filename and filetype.
The filename comprises 1 to 8 characters whilst the filetype takes the form of
a 1 to 3 character extension separated from the filename by means of a full-stop
('.'). A complete file specification (or
filespec
) thus takes the form:
[pathname]:[filename].[filetype]
