The characters SOH ($01) is used as an escape character to prefix the special character combinations. It may be followed either by a single special character, or if more than one parameter is to follow, by a count byte which specifies the number of following parameters - this may be in the form of a binary number with the top bit set, ie. count plus 128, or an ASCII code for a single decimal digit - clearly the latter is impossible for a count of more than 9. Thus the following sequences are equivalent - both move the cursor to character position (x,y):

1, '3', '@', 32+x, 32+y 1, 128+3, '@', 32+x, 32+y

NOTE: A character in single quotes is used in this section as a concise notation for a character constant, so for instance 'A' is the ASCII code for A, ie. $41 or 65 decimal. This translates into rather less elegant ASC"A" when used in BBC BASIC or its assembler, so to send the former of the above sequences to the screen from BBC BASIC one might do:

x=3: y=4 VDU 1,ASC"3", ASC"@", 32+x,32+y

1, '2', '*', <char>

(where <char> is from 'A' to 'O') draws various character such as arrows or box construction shapes (which are all boldable), with the following logic:

Each of the bottom 4 bits of 'char' represents a direction:

bit 0       decimal 1   Left
bit 1       decimal 2   Down
bit 2       decimal 4   Right
bit 3       decimal 8   Up

For example, the corner generated: VDU 1, ASC"2", ASC"*", ASC"F" makes a reasonable logical NOT sign.
 

Code			Up	Left	Down	Right	Symbol

1, '2', '*', 'A'	0	0	0	1	Pointer arrow Right
1, '2', '*', 'B'	0	0	1	0	Pointer arrow Down
1, '2', '*', 'C'	0	0	1	1	Corner Down Right
1, '2', '*', 'D'	0	1	0	0	Pointer arrow Left
1, '2', '*', 'E'	0	1	0	1	Horizontal bar
1, '2', '*', 'F'	0	1	1	0	Corner Left Down
1, '2', '*', 'G'	0	1	1	1	T Down
1, '2', '*', 'H'	1	0	0	0	Pointer arrow Up
1, '2', '*', 'I'	1	0	0	1	Corner Up Right
1, '2', '*', 'J'	1	0	1	0	Vertical unbroken bar
1, '2', '*', 'K'	1	0	1	1	T Right
1, '2', '*', 'L'	1	1	0	0	Corner Up Left
1, '2', '*', 'M'	1	1	0	1	T Up
1, '2', '*', 'N'	1	1	1	0	T Left
1, '2', '*', 'O'	1	1	1	1	Cross

To draw a horizontally and vertically divided window:

	C- -G- -F
	|   |   |

	|   |   |
	K- -O- -N
	|   |   |

	|   |   |
	I- -M- -L

With horizontal scrolling on, the row scrolls between the left and right margins when the cursor tries to go outside of the window margins else the cursor wraps from left column to right column or vice versa.

Horizontal scrolling disables vertical scrolling.

Rather than toggling these modes, they may be set or reset explicitly by prefixing them with '+' (on) or '-' (off), and a count byte of two to indicate that there are two parameters. For instance:

1, '2', '+', 'B'

sets bold on. When written in this form, modes may be combined in a list, for example:

1, '5', '-', 'B', 'F', 'T', 'U'

resets the bold, flash, tiny, underline toggles. Finally SD_DTS ($7F) deletes all toggle settings, ie. sets all toggles to off:

1, SD_DTS
 

1, '2', '+', 'R', 1, '3', '@', 32, 32, 1, '2', 'E', 52

This redefines window <n>, with the top left corner at (x,y) and horizontal and vertical sizes of w and d respectively. The values of x and y are offset from the top left corner of the application area ie. (10,0), but can be made absolute (ie. offset from the top left corner of the screen) by using 128+x, 128+y in the above sequence. E.g. for placing a window at top left corner of the screen use relative coordinates 32-10,32-0, absolute coordinates 128+0, 128+0 or mixed 128+0,32+0. It is very important that windows do not go beyond the width of the screen. To avoid the OZ window, windows should be no more than 94 6 pixel wide characters from the edge of the application window, or 104 from the leftmost edge of the screen.

1, '3', 'N', 32+n, m                Output n copies of the code m

1, '4', '!', 32+r, 32+s, 32+m       Beep sequence