7 Character Sets

This chapter describes the character sets supported by the VT510 video terminal.

7.1 Overview

The VT510 video terminal supports most character sets for Eastern Europe; Cyrillic, Greek, Hebrew, and Turkish character sets. In addition to traditional DEC and ISO character sets, which conform to the structure and rules of ISO 2022, the VT510 supports a number of IBM PC code pages (page numbers in IBM's standard character set manual) in PCTerm mode to emulate the console terminal of industry-standard PCs.

Each code page defines both the exact repertoire (set of characters) and the assignment of code positions in the 0 - 255 range. Once configured, the code page is not usually changed within a single application.

7.2 Character Sets Supported

The following sections list the characters sets supported by the VT510 terminal.

7.2.1 VT Graphic Character Sets

The VT510 supports the following VT 8-bit multinational character sets:

The VT510 also supports the following character sets:

When 7-bit NRCS Characters is selected, a corresponding 7-bit or NRC set is used depending on the keyboard language selected. (See Chapter 8 for details.)

7.2.2 PCTerm Graphic Character Sets

When PCTerm mode is selected, the terminal can still use all the VT 8-bit character sets listed in Section 7.2.1. Additionally, the following PC code pages are supported:


7-bit NRC sets are not available in PCTerm mode.

7.2.3 Control Character Sets

The following control character sets are defined in the terminal. ASCII C0 and C1 control sets have corresponding fonts for graphic representation in control representation mode.

The control representation mode font includes C0 and C1 control character set graphic representations plus DELETE (7/15), non-breaking space - NBSP (10/0), and 15/15 (total of 67 characters).

7.2.4 Character Set Structure

The VT 8-bit multinational character sets are formed from two 7-bit character set "halves." ASCII is used as the left half (GL), and the corresponding named supplemental set is used as the right half (GR). Although the character set "halves" can be designated and invoked independently, in practice, they are almost always used together. It is simpler and more convenient to think of them as a single 8-bit multinational set, although technically they are also separate 7-bit sets.

Many characters appear in more than one of the mentioned sets, so the total number of characters is far less than the sum of the individual totals. There is also a down-line loadable portion of character RAM provided for a custom soft font, a Dynamically Redefinable Character Set (DRCS). This character RAM can contain up to 2 × 96 characters.

7.2.5 Characters Not in a Character Set.

The following characters are not technically part of any of character set. They are like "control characters," but they are not in the C0 or C1 control sets.

Name Description Code Keystroke Action on Receipt
SP SPACE 32 Space Bar Treated as space
DEL DELETE 127 Delete Ctrl-8 Ignored (unless in CRM)
Reserved 160 None Error character generated
Reserved 255 None Ignored (unless in CRM)

NULL is the only fill character. (DEL and 255 are not usable as fill characters.)

If a 96-character character set is invoked into GL, then the receipt of codes 32 and 127 are part of that character set, and their graphic characters are displayed from the 96-character set. In this case, the codes 32 and 127 are not treated as SP or DEL.

If a 96-character character set is invoked into GR, the receipt of codes 160 and 255 are part of that character set, and their graphic characters are displayed from the 96-character character set. In this case, the codes 160 and 255 are not treated as an error condition or ignored, respectively.

7.3 VT Mode

All DEC character sets are supported in VT500 mode with either a VT keyboard or an attached Enhanced PC keyboard.

In VT100 mode, VT52 mode, or when 7-bit NRCS characters is selected (through Set-Up or DECNRCM), only ASCII, NRC sets, and DEC Special Graphic characters are available.

7.3.1 Selecting Character Sets

Character sets are designated with the select character set (SCS) control function. Refer to Chapter 5 for more details.

7.3.2 Character Set Mappings

The following table lists the character set mappings.

Character Set Mapped onto decimal . . .
C0 controls 0 to 31
Space 32
ASCII, all other NRC sets, Line Drawing, and DEC Technical set 33 to 126
DEL 127
C1 controls 128 to 159
10/0 160
DEC Multinational Graphic, DEC 7-Bit Greek, DEC 7-Bit Hebrew, or DEC 7-Bit Turkish 161 to 254
15/15 255
ISO Latin-1 Supplemental Graphic, ISO Latin-2 Supplemental Graphic, ISO Latin-Cyrillic, ISO Latin-Greek, ISO Latin-Hebrew, or ISO Latin-5. 160 to 255

These are typical assignments. By appropriate designating and invoking sequences, other mappings are possible for the graphic character sets.

7.4 PCTerm Mode

This section describes how to select character sets in PCTerm mode.

7.4.1 Selecting Character Sets

If a PC character set is selected, then all the SCS sequences used to designate and invoke character sets into G0, G1, G2, G3, GL, and GR (including single and locking shifts) are ignored. You select the character set through a Set-Up field or an escape sequence, DECPCTERM. You can use only one code page containing 256 characters at a time.

7.4.2 Character Set Mappings

In PC character sets, the conventional ISO C1 region, (80 hex through 9F hex) are all displayable character codes. The VT510 does not recognize control sequences that have 8-bit control codes; therefore, the 8-bit control mode becomes invalid.

C0 and C1 regions are all control codes. The C0 region (00 hex through 1F hex) in a PC character set is mixed with control characters and graphic characters. Among them, 11 locations can have both control characters and displayable characters in the same locations; other locations are occupied by displayable characters only. The 11 C0 locations include 0/5, 0/7, 0/8, 0/9, 0/A, 0/B, 0/C, 0/D, 1/1, 1/3, and 1/B.

Control codes are used for ENQ, BEL, BS, HT, LF, VT, FF, CR, DC1, DC3, and ESC operations.

You access the displayable characters by preceding the C0 control code with ESC to form a 2-byte pair (1Bh XXh). These 2-byte pairs, such as ESC 0/5, are only recognized in PCTerm mode and SCO console mode.

The C0 characters may also be displayed using the SGR sequence "CSI 11 m".

7.5 SCO Console Mode

SCO console mode can use both VT character sets and PC character sets. You select a VT character set through the PCTerm character set field in Set-Up, or you can use an SCS invocation sequence. You can select a PC character set through the same Set-Up field, or you can use the DECPCTERM escape sequence.

7.6 Soft Character Sets

The ANSI control string command to down-line load the soft character sets is DECDLD. The DECDLD command down-line loads one or more characters of a specified 94- or 96-character dynamically redefinable character set (DRCS) with a specified logical pixel pattern. The affected characters in the DRCS set also change the presentation of characters from the set currently being displayed on the screen. The DECDLD control does not clear the screen.

See Chapter 5 for a description of the DECDLD—Dynamically Redefinable Character Sets command.