ASCII

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ASCII, the American Standard Code for Information Interchange, is a 7-bit character set used in the BBC Micro series.

It includes a set of control codes for data transmission which were not relevant to the BBC Micro's display and so were reused as VDU commands.

The BBC Micro series supports 8-bit characters and so the higher order characters (values 128 to 255) are user definable in all MODEs except MODE 7. RISC OS predefines the set to ISO Latin 1 which is an 8-bit character set.

There are some differences between standard ASCII and the BBC Micro's two character sets. In MODEs 0 to 6 the backtick (`) is replaced with a pound sign (£) and the vertical bar (|) is broken (¦). On the other hand MODE 7 is a Teletext mode, whose character set is mostly ASCII with a few replaced and relocated characters. OSWRCH translates three of the ASCII characters to their Teletext equivalents before storing them in the MODE 7 screen memory.

In BASIC, ASC returns the ASCII value of a character. CHR$ creates a character from its ASCII value, and VDU prints characters by value.

Standard ASCII character set

	00	10	20	30	40	50	60	70
00	NUL	DLE	(Space)	0	@	P	`	p
01	SOH	DC1	!	1	A	Q	a	q
02	STX	DC2	"	2	B	R	b	r
03	ETX	DC3	#	3	C	S	c	s
04	EOT	DC4	$	4	D	T	d	t
05	ENQ	NAK	%	5	E	U	e	u
06	ACK	SYN	&	6	F	V	f	v
07	BEL	ETB	'	7	G	W	g	w
08	BS	CAN	(	8	H	X	h	x
09	HT	EM	)	9	I	Y	i	y
0A	LF	SUB	*	:	J	Z	j	z
0B	VT	ESC	+	;	K	[	k	{
0C	FF	FS	,	<	L	\	l	|
0D	CR	GS	-	=	M	]	m	}
0E	SO	RS	.	>	N	^	n	~
0F	SI	US	/	?	O	_	o	DEL

Differences in standard ASCII and BBC character sets

ASCII value (hex)	(decimal)	Standard character	In MODES 0 to 6	In MODE 7	Teletext value (hex)
23	35	#	#	#	5F
5B	91	[	[	←	5B
5C	92	\	\	½	5C
5D	93	]	]	→	5D
5E	94	^	^	↑	5E
5F	95	_	_	–	60
60	96	`	£	£	23
7B	123	{	{	¼	7B
7C	124	|	¦	║	7C
7D	125	}	}	¾	7D
7E	126	~	~	÷	7E

-- beardo 22:32, 7 November 2007 (UTC)