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The ZX Spectrum character set is the variant of ASCII used in the British Sinclair Spectrum computers. It is based on ASCII-1967 (the standard ASCII on which all modern character sets are based), but with one character from ASCII-1963 (the first version of ASCII), two graphics characters nonstandardly assigned, an idiosyncratic use of the control code area and use of the 128 high-bit characters beyond the ASCII range.

In the control codes area (the C0 range), the Spectrum uses its own proprietary controls, such as INK and PAPER to control foreground and background colour. The only similarity to ASCII is having cursor-left for 0x08 (ASCII Back Space) and ENTER for 0x0D (ASCII Carriage Return), which also generates an automatic linefeed. Cursor-down 0x0A (ASCII Line Feed) can be simulated with 32 spaces printed with OVER 1 (transparent overprint) and cursor-up 0x0B (ASCII Vertical Tabulation) can be simulated with 32 backspaces. The system ROM has a fault which prevents cursor-right 0x09 (ASCII Horizontal Tabulation) from working.

Control code 0x0e used to represent number in text, for speedup text processing. When spectrum text/math subsystem found 0x0e(5 bytes)<any number> it assume that 5 bytes contain converted to binary form number value following in text. If text printed to printer or display these 5 bytes ignored, but if it ussed in any mathematics expression, then this 5 bytes used and text part are ignored. (Same spectrum programs used this spectrum behavior to hide real numbers from user: Example basic command GOTO 0x0e(encoded 100)10, so when text is displayed, user see GOTO 10, but when it executed used encoded value 100 e.g. GOTO 100)

Ranges 0x00–0x05, 0x07, 0x0A–0x0C, 0x0F and 0x17–0x1F are undefined. The graphics part of the Spectrum Character Set, 0x20–0x7F, is almost standard, except that 0x60 has the pound sign (£) instead of the grave accent ( ` ) and 0x7F has the copyright sign (©) instead of the control code DEL. Note that the pound sign was mapped to 0x60, and not 0x23 as in the British variant of ASCII (ISO-646-GB), making both pound sign and number sign (#) available universally. Code 0x5E contains an up-arrow (↑) as in ASCII-1963 instead of the ASCII-1967 caret (^); however, 0x5F has an underscore and not a left-arrow.

Beyond 0x7F, the Spectrum character set uses the high-bit range, 0x80–0xFF, for its special purposes. 0x80–0x8F contain block graphics. 0x90–0xA4 contain the User Defined Graphics (UDGs), which the user can customise with a few lines of BASIC. 0xA5–0xFF contain tokens (BASIC keywords represented as single characters): for example, pressing P at the beginning of a line would generate the code 0xF6, which would cause the BASIC keyword PRINT to display on the screen. Codes 0xC7–0xC9 are the shortcuts for the mathematical operators <= (less-than-or-equal), >= (greater-than-or-equal) and <> (not-equal) respectively; unlike the relational operators of most other systems, these are characters in their own right and cannot be achieved by typing the two constituent symbols one after the other.

Mapping the printable Spectrum Character Set to Unicode is possible, but fonts containing some of the block graphics characters are still not commonplace.

The default printable characters (32 (space) to 127 (copyright)) are stored at the end of the Spectrum's ROM at memory address 15616 (0x3D00) to 16383 (0x3FFF) and are referenced by the system variable CHARS which can be found at memory address 23606/7. Interestingly, the value in CHARS is actually 256 bytes lower than the first byte of the space character so that referencing a printable ASCII character does not need to consider the first 32 characters. As such, the CHARS value (by default) holds the address 15360 (0x3C00).

The UDG characters (Gr-A to Gr-U) are stored at the end of the Spectrum's RAM at memory address 65368 (0xFF58) to 65535 (0xFFFF). As such, POKEing this address range has immediate effect on the UDG characters. The USR keyword (when followed by a single quoted character) provides a quick method to reference these addresses from BASIC. As with the printable characters, the location of the UDG characters is stored in the system variable UDG.

Codepage layout

Spectrum Character Set
0x 1x 2x 3x 4x 5x 6x 7x 8x 9x Ax Bx Cx Dx Ex Fx
x0 INK   0 @ P £ p ZXSpectrum80.svg (A) (Q) VAL USR FORMAT LPRINT LIST
x1 PAPER ! 1 A Q a q ZXSpectrum81.svg (B) (R) LEN STR$ MOVE LLIST LET
x2 FLASH " 2 B R b r ZXSpectrum82.svg (C) (S) SIN CHR$ ERASE STOP PAUSE
x3 BRIGHT # 3 C S c s ZXSpectrum83.svg (D) (T)1 COS NOT OPEN # READ NEXT
x4 INVERSE $ 4 D T d t ZXSpectrum84.svg (E) (U)2 TAN BIN CLOSE # DATA POKE
x5 OVER % 5 E U e u ZXSpectrum85.svg (F) RND ASN OR MERGE RESTORE PRINT
x6 comma/print AT & 6 F V f v ZXSpectrum86.svg (G) INKEY$ ACS AND VERIFY NEW PLOT
x7 edit TAB ' 7 G W g w ZXSpectrum87.svg (H) PI ATN <= BEEP BORDER RUN
x8 left ( 8 H X h x ZXSpectrum88.svg (I) FN LN >= CIRCLE CONTINUE SAVE
x9 right ) 9 I Y i y ZXSpectrum89.svg (J) POINT EXP <> INK DIM RANDOMIZE
xA down * : J Z j z ZXSpectrum8a.svg (K) SCREEN$ INT LINE PAPER REM IF
xB up + ; K [ k { ZXSpectrum8b.svg (L) ATTR SQR THEN FLASH FOR CLS
xC delete , < L \ l | ZXSpectrum8c.svg (M) AT SGN TO BRIGHT GO TO DRAW
xD enter - = M ] m } ZXSpectrum8d.svg (N) TAB ABS STEP INVERSE GO SUB CLEAR
xE number 3 . > N n ~ ZXSpectrum8e.svg (O) VAL$ PEEK DEF FN OVER INPUT RETURN
xF / ? O _ o © ZXSpectrum8f.svg (P) CODE IN CAT OUT LOAD COPY

(X) characters are User Definable Graphics
1 SPECTRUM under the 128K BASIC
2 PLAY under the 128K BASIC
3 Float number 4-byte mantissa and a 1 byte exponent

See also

External links

Sinclair Spectrum 48K Character SetFloating point package

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