2 I. Character Set Selection on VT220 Terminals
3 ==================================================
7 +---+ +-------------------+ +---+ +-------------------+
9 range | | | | 20h .. 7fh | | | | | a0h .. ffh |
11 +---+ +-------------------+ +---+ +-------------------+
15 SECOND /||\ "lock"- or "single"-shift one set of G0, G1, G2 or
16 STEP || G3 into one of the "displayable" charactersets GL
17 || or GR. (escape) sequences are: SI, SO, ESC ~, ESC n,
18 || ESC }, ESC o, ESC |, ESC N and ESC O.
20 +----+ +----+ +----+ +----+
21 name | G0 | | G1 | | G2 | | G3 |
22 length |(96)| |(96)| |(96)| |(96)|
23 +----+ +----+ +----+ +----+
26 /||\ designate a hard or a soft character set as
27 || one of G0, G1, G2 or G3, used escape sequences
28 FIRST || are, ESC ( X, ESC ) X, ESC * X and ESC + X - where X is
29 STEP || B for ascii, < for supplemental, 0 for special, A for
30 || british, 4 for dutch, C and 5 for finnish etc. etc. ...
33 +-----+ +------------+ +--------+ +-----------+ +------------+
34 name |ascii| |supplemental| |special | | national | |downloadable|
35 | | | graphics | |graphics| |replacement| |characterset|
36 length | (96)| | (96)| | (96)| | (96)| | (96)|
37 +-----+ +------------+ +--------+ +-----------+ +------------+
39 \-------\ /----------/ norway/danish
41 together, this is also finnish
42 referred to as the french
43 multinational character french canada
44 set (power on default german
45 on a dec vt220) italian
51 II. Emulating Character Set Selection
52 =========================================
56 just a partial emulation is done, because these boards don't allow
57 downloadable charactersets. some characters simply don't display
58 because they are not in the characterset roms on the video board.
60 if you want to change the mapping, have a look at the default tables
65 these cards have provisions for downloadable charactersets and so
66 many vt220/vt320 charactersets are fully supported:
75 when the emulator is started, it behaves initially similar to
76 the MDA/CGA/HCG method described above.
78 when a second (special) characterset for a given screen resolution
79 is loaded via the "loadfont" utility, the emulator detects this fact
80 and uses from then on extended tables to access the second charset
81 as an upper half 512 characterset in terms of ega/vga speak.
83 from this time on, vt220 downloadable fonts are usable.
85 the organization of this extended characterset is as follows:
87 0x00 ... 0x1f C0 display function fonts
88 0x20 ... 0x3f C1 display function fonts
89 0x40 ... 0x9f fonts for DEC Supplemental, DEC Special
90 Graphic, DEC Technical and ISO Latin-1
91 0xa0 ... 0xff VT220 Downloadable Font
93 the mapping between vt220 charactersets and the charactersets inside
94 the ega/vga is done by tables found in the file pcvt_tbl.h.
96 there is a MSDOS fonteditor called "EVAFONT" available on the
97 SIMTEL-20 archive, which i used to edit the character sets in the