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<TITLE>The Linux keyboard and console HOWTO: The console character sets</TITLE>
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console character sets
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character sets, console
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The kernel first tries to figure out what symbol is meant by any given
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user byte, and next where this symbol is located in the current font.
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The kernel knows about 5 translations of bytes into console-screen symbols.
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In Unicode (UTF-8) mode, the UTF-8 code is just converted directly into
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Unicode. The assumption is that almost all symbols one needs are present
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in Unicode, and for the cases where this does not hold the codes
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0xf000-0xf1ff are reserved for direct font access.
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When not in Unicode mode, one of four translation tables is used.
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The four tables are: a) Latin1 -> Unicode, b) VT100 graphics -> Unicode,
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c) PC -> Unicode, d) user-defined.
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There are two character sets, called G0 and G1, and one of them
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is the current character set. (Initially G0.)
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Typing Ctrl-N causes G1 to become current, Ctrl-O causes G0 to become current.
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These variables G0 and G1 point at a translation table, and can be changed
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by the user. Initially they point at tables a) and b), respectively.
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The sequences ESC ( B and ESC ( 0 and ESC ( U and ESC ( K cause G0 to point
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at translation table a), b), c) and d), respectively.
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The sequences ESC ) B and ESC ) 0 and ESC ) U and ESC ) K cause G1 to point
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at translation table a), b), c) and d), respectively.
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The sequence ESC c causes a terminal reset, which is what you want if the
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screen is all garbled. The oft-advised echo ^V^O will only
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make G0 current, but there is no guarantee that G0 points at table a).
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In some distributions there is a program reset(1) that just does
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echo ^[c.
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If your termcap entry for the console is correct (and has an entry
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:rs=\Ec:), then also setterm -reset will work.
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The user-defined mapping table can be set using mapscrn(8).
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The result of the mapping is that if a symbol c is printed, the symbol
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s = map[c] is sent to the video memory. The bitmap that corresponds to
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s is found in the character ROM, and can be changed using setfont(8).
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