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Text-Terminal-HOWTO: Special Features of Some Terminals NextPreviousContents9. Special Features of Some Terminals9.1 Color While the common monochrome terminal is not a colorterminal it may have a fixed "color" display other than white such asgreen or amber. All terminals have black (electron beam turned off =zero brightness). A real color terminal can change the color of thetext and background to many different colors while a monochrometerminal can only change the brightness of a fixed color.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 ona light grey background while other are highlighted by black on white.In addition there is white on black, underlining, and blinking.Color works like the color on a computer monitor or TV screen. TheCRT has three colors of dots on it with each color controlled by itsown electron beam (3 beams). Monochrome has inherently betterresolution since it doesn't depend on dots permanently fixed on thescreen. For text terminals the only use of color is to differentiatetext and this advantage is not always worth the cost of worseresolution. Thus monochrome may be better since it also costs less.9.2 Multiple Sessions For dual sessions the terminal has twoserial ports of equal status. Each port is connected to a serial porton a different computer. Thus one may log in to two differentcomputers with each session displaying in a split-screen window.Alternatively, each session may run full-screen with a "hot" key (orthe like) to switch between sessions. One could also connect to twodifferent serial ports on the same computer and log in twice (similarto "virtual terminals" at the console). The program "screen" willmake any ordinary terminal (single session) connected to a singlecomputer run two or more "sessions".9.3 Printer/Auxiliary Port Many terminals have a connector onthe rear for such a port. It may be labeled as "Aux" or "Printer",etc. Some printer ports are for parallel printers while others arefor serial printers. If a printer is connected to the printer orauxiliary port, then pressing certain keys will print the screen. Onemay also have everything that displays on the screen go also to theprinter. If the port is an auxiliary port, one may connect this toanother computer and almost have dual sessions as above. However, thevideo memory inside the terminal may not retain both sessions so youmay need to refresh the screen when switching to the other session.There will likely not be a hot key either but possibly a programmablefunction key may be programmed to do this. There exists various keycombinations and escape sequences for controlling such a port. SeePrinter Esc.There is a program called vtprint which is designed to send aprint job (text only) to your terminal to be printed on a printerattached to the terminal. It's homepage is vtprint. It's alsoincluded in the Debian distribution of Linux. xprt (also inDebian) seems to do something similar, but only for X Window terminals??Using the printer port to print may be useful if you don't have anextra port on your PC for a printer or for "point of sale" use in astore. "Transparent print mode" is where whatever the PC sends out tothe terminal goes instead to the printer. If you want the printer tobe able to send bytes to the PC (in the reverse direction) then (perWyse) it's "bidirectional mode". The Wyse "auxiliary print mode" isjust transparent print mode where the terminal screen monitors what'sbeing printed. 9.4 Pages Many terminals permit thestorage of more than one page in their video memory. Sometimes thepage size is the same as the screen, but sometimes it is larger sothat scrolling will reveal unseen parts of a page. So when one looksat a screen, there may be hidden text on the same page above or belowthe display. In addition, if there is more than just one page, theremay be hidden text on these other pages. One use for pages is onterminals that support dual sessions. Each session may have its ownpage and one may switch back and forth between them.Even if you only have a one-page-terminal with the page sized equal towhat is displayed on the screen, you will still see other pages of afile (etc.) as the host sends more data to the terminal. Oneadvantage to having additional pages stored in the terminal memory isso that you can jump to them instantly without waiting a second or sofor them to be transmitted from the host.Multiple pages is supported by ncurses. There is also a commercialprogram called "Multiscreen" which supports multiple pages butprobably not for Linux ?? Multiscreen is reported to be part of SCOand is something like the virtual terminals on a Linux PC console.The Linux program "screen" makes it look like you have multiple pagesbut they are stored in the computer and but you can have only onepage-like window for each running program. 9.5 Character-Sets A character-set is normally represented by a list (or table orchart) of characters along with the byte code assigned to eachcharacter. The codes for a byte range from 0 to 255 (00 to FF inhexadecimal). In MS-DOS, character-set tables are called"code-pages". You should examine such a table if you're not familiarwith them. They are sometimes included in printer and terminalmanuals but also are found on the Internet.Many character sets include letters from foreign languages. But theymay also include special characters used to draw boxes and otherspecial characters.ASCII was the traditional English character set used on text terminalsIt is a 7-bit code but will usually work OK even if your terminal isset to 8-bit mode. In 8-bit mode with ASCII, the high order bit isalways set to zero. Other character-sets are usually available andusually use 8-bit codes (except on very old terminals where the onlychoice is ASCII). The first half of most character-sets are theconventional 128 ASCII characters and the second half (with thehigh-order bit set to 1) belong to a wide variety of character-sets.Character sets are often ISO standards. To get specialized charactersets on a terminal, you may need to download a soft-font for thatcharacter-set into the memory of the terminal. Many terminals have anumber of built-in character sets (but perhaps not the one you need).Here are some common 8-bit character sets. CP stands for Code Pagecharacter sets invented by IBM: CP-437 (DOS ECS), ISO-8859-1(Latin-1), CP-850 (Multilingual Latin 1 --not the same as ISOLatin-1), CP-1252 (WinLatin1 = MS-ANSI). MS Windows uses CP-1252(WinLatin1) while the Internet often uses Latin-1. There are severalISO-8859- character sets in addition to Latin-1. These include Greek(-7), Arabic (-6), Eastern European (-2), and a replacement forLatin-1 (-15) called Latin-9. There are many others. For example,KOI8-R is more commonly used for Russian than IS0-8859-5. Unicode isa very large character-set where each character is represented by 2bytes instead on just one byte.More info re character-sets are: Manual pages: charsets, iso_8859-l or latin1 (covers 8859 series), ascii HOWTO's for various languages (often written in that language). ISO-8859 Alphabet Soup More than just iso8859. Extensive. A tutorial on character code issues Clearly written. Languages, Countries and Character Sets Languages of the World by Computers ... ... International Character SetsOnce you've found the character set name (or alpha-numericdesignation) you are interested in, you may search for more info aboutit on the Internet.Graphics (Line Drawing, etc.) There are special charactersfor drawing boxes, etc. There are also numerous non-ASCII symbolssuch 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 vt100terminals). Your terminfo may be set up to use them. But if you seea row of letters when there should be a line, it may mean thatterminfo hasn't implemented them.You need to know the following if your graphics don't work right. Thedefault graphic character set is the vt-100 ANSI graphics. Otherwisethe string acsc must be defined in your terminfo. It establishes amap between the vt-100 graphic characters codes and the actual codesused on your terminal. So even if your terminal doesn't have thevt-100 graphics, it can likely still generate such graphics with someother character set. If terminfo has it right, this will happenautomatically.If character sets must be switched then the terminfo variables: enacs,rmacs, and smacs should be defined. Note acs = Alternate CharacterSet. Even if the upper half of the normal character set contains thegraphic characters it may be considered a separate 7-bit character setthat needs to be switched to.National Replacement Characters (obsolete) In the 1960's,the ASCII 7-bit code was devised to map 7-bit bytes to Englishletters, numbers, punctuation marks, etc. Other countries adoptedASCII, but most of them had some additional letters which were notpresent in the ASCII code. What to do? Various people decided topurge certain symbols (such as ^, }) from ASCII and to substitutenational letters (ones with dots over them, etc.) for the ASCIIletters. In other words they replaced ASCII letters with "NationalReplacement Characters"There were a lot of problems with this, since it was done mostly bycompanies which sold computer terminals with a resulting lack ofstandardization. Another problem was that sometimes the purgedsymbols were needed. This problem was solved in the 1980's and 1990'swith the adoption of 8-bits/byte character sets which had many moreletters.Many West-European languages only needed several additional letterswhich were not in ASCII. To get them in 7-bit code, they borrowed thecodes for seldom used ASCII symbols: @ [ \ ] ^ ` { \} ~ The symbols $ and # are sometimes used also. Sowhen using these replacement character sets, you are deprived of usingcertain of these ASCII symbols since they now are used for the newnon-ASCII letters. Now that 8-bit character codes have replaced 7-bitones, it's better to use an 8-bit code which has both all the ASCIIsymbols plus the non-ASCII characters for various languages. There'salso Unicode which replaces 8-bit codes with the same code scheme tocover all languages (well almost all significant ones).ISO-646 (for 1972 and later) permitted using National ReplacementCharacters (7-bit). It specified that the above mentioned charactercodes may be borrowed, but doesn't specify which national charactersare to replace them. Some countries standardized the replacementsby registering them with ECMA.Many terminals exist which support these national replacementcharacters but you probably don't want to implement this supportunless you have some old files to read. Very old terminals may onlysupport the national characters for the country in which they weresold. Later terminals offered a choice of languages. Modem terminalsare 8-bit and don't need "national replacements". Replacementcharacters 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).Here's tables for some character sets taken from Kermit and Unisysdocuments: Swedish DanishASCII 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 -------- diaeresisASCII 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 --------9.6 Fonts Most terminals made after the mid 1980's can accept downloadedsoft-font. This means that they can display almost any character setprovided that you can find the soft-font for it. If you can't findthe needed soft-font, you can always create your own. A free fonteditor for this is called BitFontEdit (written by the author of thisdocument) and is at athttp://www.ibiblio.org/pub/Linux/utils/terminal/For mapping the keyboard (and screen) for use of various fonts seeCharacter Mapping: mapchan9.7 Keyboards & Special KeysTerminal keyboards often have a number of keys that one doesn't findon a PC keyboard. Few (if any) actual terminals will have all ofthese keys and most will have additional keys not listed here. Somehave a large number of special purpose keys such as terminals made foruse with cash registers. There are often many more key meanings thanshown here since these keys often have extended meanings when used inconjunction with other keys (such as shift and control). BREAK sends a very long 0 bit (space = +12 V) of duration 300to 700 milliseconds to the host. The host may interpret this as aninterrupt if stty has set brkint or ignore it if ignbrk is set. NO SCROLL stops the screen from scrolling like ^S does.Depressing it again resumes scrolling. Uses flow control signals todo this. REPEAT if held down with an other key, forces repeated output ofthat other key even if the auto-repeat option is set to off. LINE FEED sends the line feed character ^J to the host. Seldomused. SET-UP allows the manual configuration of the terminal viamenus. Sometimes purposely disabled by putting a block under it so itcan't be pressed down. Sometimes another key such as shift or controlmust be pressed at the same time. See Getting Into Set-Up (Configuration) Mode. LOCAL disconnects the terminal from the host. In local, whatone types goes directly to the screen. Useful for testing. RETURN is the same as the "enter" key on a PC. It usuallysends a carriage return to the host which normally get translated to anew-line character by the host's device driver. On some terminals itmay be set up to send something else. F1, F2, ... or PF1, PF2, ... are function keys which sometimesmay be programmed to send out a sequence of bytes (characters). SeeFunction Keys9.8 Mouse 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.For a mouse on VT terminals see http://www.cs.utk.edu/~shuford/terminal/dec_vt_mouse.html Theseescape codes for mice are called "DEC Locator sequences". The FALCOInfinity Series of terminals, model ANSI-G supports it. Do any linuxapplications support this ?? NextPreviousContents |
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