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<H2><A NAME="s9">9.</A> <A HREF="Text-Terminal-HOWTO.html#toc9">Special Features/Types of Some Terminals</A></H2>
<H2><A NAME="ss9.1">9.1</A> <A HREF="Text-Terminal-HOWTO.html#toc9.1">Terminal Uses a PC Monitor</A>
</H2>
<P>One may use a PC (including it's monitor) to emulate a terminal.
But PCs have become so powerful that only a small portion of the PC's
capacity is utilized to run the emulation. So why not make a tiny PC
that has low computing capability so it is barely able do the task of
emulating a terminal. Then call this tiny device a text terminal and
point out that one must supply and plug in a PC monitor in order to
use this terminal. Such devices exist and are only about an inch
high. They are sometimes referred to as small footprint terminals.
Their advantage is that they are cheap, take up little space, and
might be able to use surplus monitors that otherwise might be
discarded.</P>
<H2><A NAME="ss9.2">9.2</A> <A HREF="Text-Terminal-HOWTO.html#toc9.2">Color </A>
</H2>
<H3>Emulated text terminals</H3>
<P>In contrast to the monochrome or most real text terminals, an
emulated text terminal usually has colors since it displays on a PC
color monitor. See
<A HREF="Text-Terminal-HOWTO-10.html#colors">Colors on Emulated Terminals</A></P>
<H3>Old real text terminal</H3>
<P>Some real terminals had color displays but most had either no color
or fixed "color" displays other than white such as green or amber. All
terminals had black (electron beam turned off = zero brightness). A
real color terminal can change the color of the text and background to
many different colors while a monochrome terminal can only change the
brightness of a fixed color.</P>
<P>However, changing the brightness, etc. gives a lot of possibilities.
For example, a black and white (monochrome) terminal can have white,
grey, and black by varying the brightness. Some words can be black on
a light grey background while other are highlighted by black on white.
In addition there is white on black, underlining, and blinking.</P>
<P>Real color works like the color on a computer monitor or TV screen.
The CRT has three colors of dots permanently on it with the brightness
of each color controlled by its own electron beam (3 beams). The
monochrome of real text terminals had inherently better resolution
since it didn't depend on dots permanently fixed on the screen. For
text terminals the only use of color is to differentiate text and this
advantage was often not worth the cost of worse resolution. Thus
monochrome may have historically been better since it also cost less.
But today color displays have are ubiquitous and have improved in
resolution since the olden days of the real text terminal.</P>
<H2><A NAME="ss9.3">9.3</A> <A HREF="Text-Terminal-HOWTO.html#toc9.3">Multiple Sessions </A>
</H2>
<P> For dual sessions the terminal has two
serial ports of equal status. Each port is connected to a serial port
on a different computer. Thus one may log in to two different
computers with each session displaying in a split-screen window.
Alternatively, each session may run full-screen with a "hot" key (or
the like) to switch between sessions. One could also connect to two
different serial ports on the same computer and log in twice (similar
to "virtual terminals" at the console). The program "screen" will
make any ordinary terminal (single session) connected to a single
computer run two or more "sessions".</P>
<H2><A NAME="ss9.4">9.4</A> <A HREF="Text-Terminal-HOWTO.html#toc9.4">Printer/Auxiliary Port </A>
</H2>
<P> Many terminals have a connector on
the rear for such a port. It may be labeled as "Aux" or "Printer",
etc. Some printer ports are for parallel printers while others are
for serial printers. If a printer is connected to the printer or
auxiliary port, then pressing certain keys will print the screen. One
may also have everything that displays on the screen go also to the
printer. If the port is an auxiliary port, one may connect this to
another computer and almost have dual sessions as above. However, the
video memory inside the terminal may not retain both sessions so you
may need to refresh the screen when switching to the other session.
There will likely not be a hot key either but possibly a programmable
function key may be programmed to do this. There exists various key
combinations and escape sequences for controlling such a port. See
<A HREF="Text-Terminal-HOWTO-22.html#printer_esc">Printer Esc</A>.</P>
<P>There is a program called <CODE>vtprint</CODE> which is designed to send a
print job (text only) to your terminal to be printed on a printer
attached to the terminal. It's homepage is <CODE>
<A HREF="http://vtprint.sourceforge.net/">vtprint</A></CODE>. It's also
included in the Debian distribution of Linux. <CODE>xprt</CODE> (also in
Debian) seems to do something similar, but only for X Window terminals
??</P>
<P>Using the printer port to print may be useful if you don't have an
extra port on your PC for a printer or for "point of sale" use in a
store. "Transparent print mode" is where whatever the PC sends out to
the terminal goes instead to the printer. If you want the printer to
be able to send bytes to the PC (in the reverse direction) then (per
Wyse) it's "bidirectional mode". The Wyse "auxiliary print mode" is
just transparent print mode where the terminal screen monitors what's
being printed.</P>
<H2><A NAME="pages_"></A> <A NAME="ss9.5">9.5</A> <A HREF="Text-Terminal-HOWTO.html#toc9.5">Pages </A>
</H2>
<P> Many terminals permit the
storage of more than one page in their video memory. Sometimes the
page size is the same as the screen, but sometimes it is larger so
that scrolling will reveal unseen parts of a page. So when one looks
at a screen, there may be hidden text on the same page above or below
the display. In addition, if there is more than just one page, there
may be hidden text on these other pages. One use for pages is on
terminals that support dual sessions. Each session may have its own
page and one may switch back and forth between them.</P>
<P>Even if you only have a one-page-terminal with the page sized equal to
what is displayed on the screen, you will still see other pages of a
file (etc.) as the host sends more data to the terminal. One
advantage to having additional pages stored in the terminal memory is
so that you can jump to them instantly without waiting a second or so
for them to be transmitted from the host.</P>
<P>Multiple pages is supported by ncurses. There is also a commercial
program called "Multiscreen" which supports multiple pages but
probably not for Linux ?? Multiscreen is reported to be part of SCO
and is something like the virtual terminals on a Linux PC console.
The Linux program "screen" makes it look like you have multiple pages
but they are stored in the computer and but you can have only one
page-like window for each running program.</P>
<H2><A NAME="char_sets"></A> <A NAME="ss9.6">9.6</A> <A HREF="Text-Terminal-HOWTO.html#toc9.6">Character-Sets </A>
</H2>
<P> A character-set is normally represented by a list (or table or
chart) of characters along with the byte code assigned to each
character. The codes for a byte range from 0 to 255 (00 to FF in
hexadecimal). In MS-DOS, character-set tables are called
"code-pages". You should examine such a table if you're not familiar
with them. They are sometimes included in printer and terminal
manuals but also are found on the Internet.</P>
<P>Many character sets include letters from foreign languages. But they
may also include special characters used to draw boxes and other
special characters.</P>
<P>ASCII was the traditional English character set used on text terminals
It is a 7-bit code but will usually work OK even if your terminal is
set to 8-bit mode. In 8-bit mode with ASCII, the high order bit is
always set to zero. Other character-sets are usually available and
usually use 8-bit codes (except on very old terminals where the only
choice is ASCII). The first half of most character-sets are the
conventional 128 ASCII characters and the second half (with the
high-order bit set to 1) belong to a wide variety of character-sets.
Character sets are often ISO standards. To get specialized character
sets on a terminal, you may need to download a soft-font for that
character-set into the memory of the terminal. Many terminals have a
number of built-in character sets (but perhaps not the one you need).</P>
<P>Here are some common 8-bit character sets. CP stands for Code Page
character sets invented by IBM: CP-437 (DOS ECS), ISO-8859-1
(Latin-1), CP-850 (Multilingual Latin 1 --not the same as ISO
Latin-1), CP-1252 (WinLatin1 = MS-ANSI). MS Windows uses CP-1252
(WinLatin1) while the Internet often uses Latin-1. There are several
ISO-8859- character sets in addition to Latin-1. These include Greek
(-7), Arabic (-6), Eastern European (-2), and a replacement for
Latin-1 (-15) called Latin-9. There are many others. For example,
KOI8-R is more commonly used for Russian than IS0-8859-5. Unicode is
a very large character-set where each character is represented by 2
bytes instead on just one byte.</P>
<P>More info re character-sets are:
<UL>
<LI> Manual pages: charsets, iso_8859-l or latin1 (covers 8859 series), ascii</LI>
<LI> HOWTO's for various languages (often written in that language).</LI>
<LI>
<A HREF="http://czyborra.com/charsets/iso8859.html">ISO-8859 Alphabet Soup</A> More than just iso8859. Extensive.</LI>
<LI>
<A HREF="http://www.cs.tut.fi/~jkorpela/chars.html">A tutorial on character code issues</A> Clearly written.</LI>
<LI>
<A HREF="http://www.w3.org/International/O-charset-lang.html">Languages, Countries and Character Sets</A></LI>
<LI>
<A HREF="http://www.osk.3web.ne.jp/logos/">Languages of the World by Computers ...</A></LI>
<LI>
<A HREF="ftp://kermit.columbia.edu/kermit/e/isok7.txt">... International Character Sets</A></LI>
</UL>
</P>
<P>Once you've found the character set name (or alpha-numeric
designation) you are interested in, you may search for more info about
it on the Internet.</P>
<H3>Graphics (Line Drawing, etc.) </H3>
<P> There are special characters
for drawing boxes, etc. There are also numerous non-ASCII symbols
such as bullets. These may either be part of an 8-bit character set
(such as WinLatin1 = CP-1252) or provided as a separate font (in vt100
terminals). Your terminfo may be set up to use them. But if you see
a row of letters when there should be a line, it may mean that
terminfo hasn't implemented them.</P>
<P>You need to know the following if your graphics don't work right. The
default graphic character set is the vt-100 ANSI graphics. Otherwise
the string acsc must be defined in your terminfo. It establishes a
map between the vt-100 graphic characters codes and the actual codes
used on your terminal. So even if your terminal doesn't have the
vt-100 graphics, it can likely still generate such graphics with some
other character set. If terminfo has it right, this will happen
automatically.</P>
<P>If character sets must be switched then the terminfo variables: enacs,
rmacs, and smacs should be defined. Note acs = Alternate Character
Set. Even if the upper half of the normal character set contains the
graphic characters it may be considered a separate 7-bit character set
that needs to be switched to.</P>
<H3>National Replacement Characters (obsolete) </H3>
<P> In the 1960's,
the ASCII 7-bit code was devised to map 7-bit bytes to English
letters, numbers, punctuation marks, etc. Other countries adopted
ASCII, but most of them had some additional letters which were not
present in the ASCII code. What to do? Various people decided to
purge certain symbols (such as ^, }) from ASCII and to substitute
national letters (ones with dots over them, etc.) for the ASCII
letters. In other words they replaced ASCII letters with "National
Replacement Characters"</P>
<P>There were a lot of problems with this, since it was done mostly by
companies which sold computer terminals with a resulting lack of
standardization. Another problem was that sometimes the purged
symbols were needed. This problem was solved in the 1980's and 1990's
with the adoption of 8-bits/byte character sets which had many more
letters.</P>
<P>Many West-European languages only needed several additional letters
which were not in ASCII. To get them in 7-bit code, they borrowed the
codes for seldom used ASCII symbols:<BR> @ [ \ ] ^ ` { \
} ~<BR> The symbols $ and # are sometimes used also. So
when using these replacement character sets, you are deprived of using
certain of these ASCII symbols since they now are used for the new
non-ASCII letters. Now that 8-bit character codes have replaced 7-bit
ones, it's better to use an 8-bit code which has both all the ASCII
symbols plus the non-ASCII characters for various languages. There's
also Unicode which replaces 8-bit codes with the same code scheme to
cover all languages (well almost all significant ones).</P>
<P>ISO-646 (for 1972 and later) permitted using National Replacement
Characters (7-bit). It specified that the above mentioned character
codes may be borrowed, but doesn't specify which national characters
are to replace them. Some countries standardized the replacements
by registering them with ECMA.</P>
<P>Many terminals exist which support these national replacement
characters but you probably don't want to implement this support
unless you have some old files to read. Very old terminals may only
support the national characters for the country in which they were
sold. Later terminals offered a choice of languages. Modem terminals
are 8-bit and don't need "national replacements". Replacement
characters exist for the following languages/countries: British, Cuba
(Spanish), Dutch, Finnish, French, French Canadian, German, Hebrew,
Hungarian, Italian, Norwegian/Danish, Portuguese, Spanish, Swedish,
Swiss (German).</P>
<P>Here's tables for some character sets taken from Kermit and Unisys
documents:</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
Swedish Danish
ASCII German Finnish Norwegian French
@ at-sign section ------- ------- a-grave
[ left-bracket A-diaeresis A-diaeresis AE-digraph degree
/ backslash O-diaeresis O-diaeresis O-slash c-cedilla
] right-bracket U-diaeresis A-circle A-circle section
^ circumflex ------ U-diaeresis ------- -------
` accent-grave ------ e-acute ------- -------
{ left-brace a-diaeresis a-diaeresis ae-digraph e-acute
| vertical-bar o-diaeresis o-diaeresis o-circle u-grave
} right-brace u-diaeresis a-circle a-circle e-grave
~ tilde ess-zet u-diaeresis -------- diaeresis
ASCII Italian Spanish
@ at-sign section section
[ left-bracket degree inverted-exclamation
/ backslash #-pound N-tilde
] right-bracket e-acute inverted-question-mark
^ circumflex ------- -------
` accent-grave u-grave -------
{ left-brace a-grave degree
| vertical-bar o-grave n-tilde
} right-brace e-grave --------
~ tilde i-grave --------
</PRE>
</CODE></BLOCKQUOTE>
</P>
<H2><A NAME="ss9.7">9.7</A> <A HREF="Text-Terminal-HOWTO.html#toc9.7">Fonts</A>
</H2>
<P> Most terminals made after the mid 1980's can accept downloaded
soft-font. This means that they can display almost any character set
provided that you can find the soft-font for it. If you can't find
the needed soft-font, you can always create your own. A free font
editor for this is called BitFontEdit (written by the author of this
document) and is at at<BR>
<A HREF="http://www.ibiblio.org/pub/Linux/utils/terminal/">http://www.ibiblio.org/pub/Linux/utils/terminal/</A><BR>
For mapping the keyboard (and screen) for use of various fonts see
<A HREF="Text-Terminal-HOWTO-15.html#mapchan_">Character Mapping: mapchan</A></P>
<H2><A NAME="ss9.8">9.8</A> <A HREF="Text-Terminal-HOWTO.html#toc9.8">Keyboards &amp; Special Keys</A>
</H2>
<P>Terminal keyboards often have a number of keys that one doesn't find
on a PC keyboard. Few (if any) actual terminals will have all of
these keys and most will have additional keys not listed here. Some
have a large number of special purpose keys such as terminals made for
use with cash registers. There are often many more key meanings than
shown here since these keys often have extended meanings when used in
conjunction with other keys (such as shift and control).</P>
<P>
<UL>
<LI> BREAK sends a very long 0 bit (space = +12 V) of duration 300
to 700 milliseconds to the host. The host may interpret this as an
interrupt if stty has set brkint or ignore it if ignbrk is set.
</LI>
<LI> NO SCROLL stops the screen from scrolling like ^S does.
Depressing it again resumes scrolling. Uses flow control signals to
do this.
</LI>
<LI> REPEAT if held down with an other key, forces repeated output of
that other key even if the auto-repeat option is set to off.
</LI>
<LI> LINE FEED sends the line feed character ^J to the host. Seldom
used.
</LI>
<LI> SET-UP allows the manual configuration of the terminal via
menus. Sometimes purposely disabled by putting a block under it so it
can't be pressed down. Sometimes another key such as shift or control
must be pressed at the same time. See
<A HREF="Text-Terminal-HOWTO-14.html#enter_setup">Getting Into Set-Up (Configuration) Mode</A>.
</LI>
<LI> LOCAL disconnects the terminal from the host. In local, what
one types goes directly to the screen. Useful for testing.
</LI>
<LI> RETURN is the same as the "enter" key on a PC. It usually
sends a carriage return to the host which normally get translated to a
new-line character by the host's device driver. On some terminals it
may be set up to send something else.
</LI>
<LI> F1, F2, ... or PF1, PF2, ... are function keys which sometimes
may be programmed to send out a sequence of bytes (characters). See
<A HREF="Text-Terminal-HOWTO-14.html#funct_keys">Function Keys</A></LI>
</UL>
</P>
<H2><A NAME="ss9.9">9.9</A> <A HREF="Text-Terminal-HOWTO.html#toc9.9">Mouse</A>
</H2>
<P> A few text-terminals support a mouse. When the mouse is clicked,
an escape sequence is sent to the host to tell it where the mouse is.
An article for a mouse on VT terminals was once at
http://www.cs.utk.edu/&nbsp;shuford/terminal/dec_vt_mouse.html but it's now a
dead link (2013). Try the "Wayback" machine." These escape codes for
mice are called "DEC Locator sequences". The FALCO Infinity Series of
terminals, model ANSI-G supports it. Did any linux applications support
this ?? </P>
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