ZX80 character set

The ZX80 character set is the character encoding used by the Sinclair Research ZX80 microcomputer with its original 4K BASIC ROM. The encoding uses one byte per character for 256 code points. It has no relationship with previously established ones like ASCII or EBCDIC, but it is related though not identical to the character set of the successor ZX81.

Printable characters

The character set has 64 unique glyphs present at code points 0–63. With the most significant bit set the character is generated in inverse video; corresponding to code points 128–191. These 128 values are the only displayable ones allowed in the video memory (known as the display file). The remaining code points (64–127 and 192–255) are used as control characters such as 118 for newline, or uniquely to Sinclair BASIC for keywords, while some are unused.

The small effective range of only 64 unique glyphs precludes support for Latin lower case letters, and many symbols used widely in computing such as the exclamation point or the at sign.

There are 11 block graphics characters, counting code point 0 which also doubles as space. Together with the 11 inverse video versions these 22 code points provide every combination of the character cell divided into 2×2 black-and-white block pixels for low-resolution 64×48 pixel graphics, or into 1×2 black, white or dithered gray wide block pixels for a 32×48 resolution. The 2×2 versions of these are also present in the Block Elements Unicode block.

Code point 1 is the double-quote (") character when used in the display file, but uniquely to the ZX80 it is used internally as the string terminator character^[1] so the BASIC function CHR$(1) returns a null string;^[2] CHR$(212) translates to the printable " character.^[3]

Changes in the ZX81

The 8K BASIC ROM of the follow-up ZX81 model was also available as an upgrade for the ZX80, replacing its integer-only 4K BASIC ROM.^[4] It introduced the modified ZX81 character set which has mostly the same code points, e.g. for A-Z and 0-9, but the code points are different for the block graphics characters, the symbols ", -, +, *, /, =, >, <, and the BASIC keyword tokens (with many new added). There are also changes to the control characters and code point 1 is no longer an unprintable string terminator.

In the later Sinclair ZX Spectrum the entire character encoding was replaced with the ZX Spectrum character set, which is a derivative of ASCII and includes lower case letters and more.

System font

The ZX80 system font uses an 8×8 pixel-per-character grid where most glyphs fit in 7×6 pixels leaving one pixel horizontal space between them. This font was modified in the ZX81's ROM to slightly narrower 6×6 pixel glyphs with two pixels horizontal space between them, which improved the look of single inverted characters by showing inverted pixels on both sides. Some glyphs also received a different design in the ZX81 system font, noticeable on the *, the slashed and less rounded 0, and the less rounded $, C, G and J.

Layout

Legend:

Alphabetic   Control character   Numeric digit   Punctuation

Extended punctuation   Graphic character   International   Undefined

ZX80 character set^{[1][3][lower-alpha 1]}

	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F
0_	SP U+0020 0	" U+0022 1[lower-alpha 2]	U+258C 2	U+2584 3	U+2598 4	U+259D 5	U+2596 6	U+2597 7	U+259E 8	U+2592 9[lower-alpha 3]	10[lower-alpha 4]	11[lower-alpha 4]	£ U+00A3 12	$ U+0024 13	: U+003A 14	? U+003F 15
1_	( U+0028 16	) U+0029 17	- U+002D 18	+ U+002B 19	* U+002A 20	/ U+002F 21	= U+003D 22	> U+003E 23	< U+003C 24	; U+003B 25	, U+002C 26	. U+002E 27	0 U+0030 28	1 U+0031 29	2 U+0032 30	3 U+0033 31
2_	4 U+0034 32	5 U+0035 33	6 U+0036 34	7 U+0037 35	8 U+0038 36	9 U+0039 37	A U+0041 38	B U+0042 39	C U+0043 40	D U+0044 41	E U+0045 42	F U+0046 43	G U+0047 44	H U+0048 45	I U+0049 46	J U+004A 47
3_	K U+004B 48	L U+004C 49	M U+004D 50	N U+004E 51	O U+004F 52	P U+0050 53	Q U+0051 54	R U+0052 55	S U+0053 56	T U+0054 57	U U+0055 58	V U+0056 59	W U+0057 60	X U+0058 61	Y U+0059 62	Z U+005A 63
4_
5_
6_
7_	UP 112	DOWN 113	LEFT 114	RIGHT 115	HOME 116	EDIT 117	NEW LINE 118	RUB OUT 119
8_	U+2588 128	" 129	U+2590 130	U+2580 131	U+259F 132	U+2599 133	U+259C 134	U+259B 135	U+259A 136	U+2592 137[lower-alpha 3]	138[lower-alpha 4]	139[lower-alpha 4]	£ 140	$ 141	: 142	? 143
9_	( 144	) 145	- 146	+ 147	* 148	/ 149	= 150	> 151	< 152	; 153	, 154	. 155	0 156	1 157	2 158	3 159
A_	4 160	5 161	6 162	7 163	8 164	9 165	A 166	B 167	C 168	D 169	E 170	F 171	G 172	H 173	I 174	J 175
B_	K 176	L 177	M 178	N 179	O 180	P 181	Q 182	R 183	S 184	T 185	U 186	V 187	W 188	X 189	Y 190	Z 191
C_
D_					" 212[lower-alpha 2]	THEN 213[lower-alpha 5]	TO 214[lower-alpha 5]	; 215	, 216	( 217	) 218	NOT 219[lower-alpha 5]	- 220	+ 221	* 222	/ 223
E_	AND 224[lower-alpha 5]	OR 225[lower-alpha 5]	** 226[lower-alpha 6]	= 227	> 228[lower-alpha 1]	< 229[lower-alpha 1]	LIST 230[lower-alpha 5]	RETURN 231[lower-alpha 5]	CLS 232[lower-alpha 5]	DIM 233[lower-alpha 5]	SAVE 234[lower-alpha 5]	FOR 235[lower-alpha 5]	GO TO 236[lower-alpha 5]	POKE 237[lower-alpha 5]	INPUT 238[lower-alpha 5]	RAND OMISE 239[lower-alpha 5]
F_	LET 240[lower-alpha 5]			NEXT 243[lower-alpha 5]	PRINT 244[lower-alpha 5]		NEW 246[lower-alpha 5]	RUN 247[lower-alpha 5]	STOP 248[lower-alpha 5]	CONT INUE 249[lower-alpha 5]	IF 250[lower-alpha 5]	GO SUB 251[lower-alpha 5]	LOAD 252[lower-alpha 5]	CLEAR 253[lower-alpha 5]	REM 254[lower-alpha 5]
	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F

Notes

1. The ZX80 Operating Manual has an error and shows the > and < symbols in the wrong order.^[5]
2. Code point 1 is the double-quote (") symbol when used in the video memory (called the display file), but it is used internally as the string terminator character^[1] so CHR$(1) returns a null string. Code point 212, CHR$(212), translates to the printable " character.
3. Because they are 50% gray rasters, code points 9 and 137 have the same appearance although every pixel is inverted. Both can be expressed as Unicode character U+2592 ("Medium shade") in the Block Elements Unicode block, but of course if both are converted to the same code point the conversion is non-reversible.
4. Not in the Block Elements Unicode block.
5. Sinclair BASIC tokenizes keywords into single-byte code points.
6. The raise to a power multi-character operator tokenized into a single-byte code point.

References

1. Wearmouth, Geoff. "An Assembly Listing of the ROM of the Sinclair ZX80". Archived from the original on August 15, 2015.
2. Davenport, Hugo (1980). A Course in BASIC Programming - Sinclair ZX80 Operating Manual. Science of Cambridge Ltd. pp. 75–77.
3. Davenport, Hugo (1980). A Course in BASIC Programming - Sinclair ZX80 Operating Manual. Science of Cambridge Ltd. pp. 116–117.
4. "8K BASIC ROM UPGRADE".
5. http://www.oocities.org/peterochocki/computers/sinclair/zx80char.htm

See also

• ZX81 character set
• ZX Spectrum character set
• ATASCII
• Atari ST character set
• PETSCII
• Extended ASCII