J.E.Lawrie HINTS-20.
V.2
Extracts from "Z88 Portable Computing" by Dave Oborne - Sigma Press,
ISBN: 1-85058-204-1
Controlling the screen
As well as giving you full control over your printed output, BBC Basic lets
you fine-tune your screen display to such an extent that you can control the
cursor movement, create windows, and define your own characters. This is
all done using a very powerful statement: VDU
The VDU statement comes in two forms. It is either followed by a single
value or a sequence of values.
When the VDU statement (which can be shortened to V.) is followed by a
single value between 0 and 127 it `prints' the ASCII character associated
with that value to the screen - although sometimes the action might be to
move the cursor or ring a bell rather than printing visible characters. VDU
97, for example will print `a'; VDU 36 prints `$' but more often the use
will be for the following attributes :-
VDU7 makes the Z88 beep
VDU8 moves the cursor back one space
VDU9 moves the cursor forward one space
VDU10 moves the cursor down one line
VDU11 moves the cursor up one line
VDU12 clears the text area
VDU13 moves the cursor to the start of the current line
(note - VDU1,50 moves it to the end of this line)
VDU127 prints a black square
VDU160 prints three dots (as does <>SPCBAR)
They can be used in sequence as in the following :-
10 VDU9,9,9,127,127,127
20 VDU10,8,163,10,8,163
30 VDU8,8,163,8,8,163,8
40 VDU11,127,10,10,127
Extended Sequences
To use the extended form of VDU statements the first number of the sequence
must always be 1. This facility opens a range of possibilities for
controlling the screen display. With it you can generate special
characters, set text attributes, define text justification and create
windows.
Cursor Movement:
You can send the cursor directly to a particular position on the screen by
using the VDU command:
VDU1,51,64,32+x,32+y
where x and y are the column and row numbers respectively, e.g. to put the
cursor in the middle of the screen you would use:
VDU1,51,64,80,36
Special sequence VDU1,50,88,32+x moves the cursor to position `x' in the
same row. VDU1,50,89,32+y moves it to row `y' in the same column
Special Characters
VDU1,32 Three dots VDU1,240 An outline arrow - left
VDU1,33 The Z88 bell symbol VDU1,241 " " " - right
VDU1,39 The grave accent VDU1,242 " " " - down
VDU1,42 Square VDU1,243 " " " - up
VDU1,43 Diamond VDU1,244 A bullet arrow - left
VDU1,45 The Z88 SHIFT symbol VDU1,245 " " " - right
VDU1,124 An unbroken vertical line VDU1,246 " " " - down
VDU1,224 The Z88 SPACE symbol VDU1,247 " " " - up
VDU1,225 The Z88 ENTER symbol VDU1,248 A left pointer
VDU1,226 The Z88 TAB symbol VDU1,249 A right pointer
VDU1,227 The Z88 DEL symbol VDU1,250 A down pointer
VDU1,228 The Z88 ESC symbol VDU1,251 An up pointer
VDU1,229 The Z88 MENU symbol
VDU1,230 The Z88 INDEX symbol
VDU1,231 The Z88 HELP symbol
Text Attributes
In addition to these characters, other attributes can be set. The first
time the command is encountered it is set `on', the next time is `off'. i.e
the attribute is "toggled".
VDU1,66 Bold VDU1,67 Cursor VDU1,70 Flash
VDU1,71 Grey print VDU1,76 Caps lock VDU1,82 Inverse video
VDU1,83 Vertical scroll VDU1,84 Tiny font VDU1,85 Underline
VDU1,87 Horizontal scrolling
VDU1,127,1,67,1,83 Resets all toggles to the established standard.
Note - VDU1,127 Sets ALL toggles to `off', then 1,67 and 1,83
reset the cursor and scrolling back to `on'.
Using another extended VDU sequence it is possible to force a complete set
of attributes to be switched on or off at the same time -
to turn attributes on: VDU1,49+n,43,sequence of codes
to turn attributes off: VDU1,49+n,45,sequence of codes
`n' represents the number of attribute codes to be turned on or off.
So, to turn on reverse video and tiny font, you use the sequence -
VDU1,51,43,82,84 or, to turn off the cursor, VDU1,50,45,67
( 51 = 49 + 2 ) ( 50 = 49 + 1 )
Finally, it is possible to set certain attributes for a specific
number of characters already onscreen - though only applying to grey,
flashing, reverse and underlining it can save considerable time - -
VDU1,50,65,32+n applies the current toggle to the next `n' charac's.
VDU1,50,69,32+n inverts the current toggles for the next `n' char's.
Windows
The Z88 makes considerable use of windows within its various applications.
For example, the INDEX, RAMs, DIARY, CALCULATOR, etc. Within Basic you can
define up to six such windows, referred to simply from 1 to the number of
windows you have.
The following sequence defines a window:
VDU1, 55, 35, 48+n, 32+x, 32+y, 32+w, 32+d, type
(spaces are only for greater clarity)
n is the window number
x is the start column (left hand) of the window
y is the start row (top) of the window
w is the width of the window
type is the type of window, defined as:
129 draw left and right margin lines
130 draw shelf brackets (blocks at the top of left and right lines)
131 draw margin lines AND shelf brackets
Once you have defined a window you can send information to it by using
one of the following VDU sequences:
VDU1,50,72,48+n Direct output to window `n', maintaining the
display attributes previously set for this window.
VDU1,50,73,48+n Direct output to window `n', resetting attributes
to their default state.
VDU1,50,67,48+n Direct output to window `n', resetting attributes
to default and clearing the window.
When text and other information is sent to a window, the normal scrolling
functions of the display are turned off. Remember though, that both
horizontal and vertical scrolling can be turned on using the
previously-described attribute sequences. So, to turn vertical scrolling
on/off use VDU1,83 and horizontal scrolling with VDU1,87
To force a scrolling movement of a window, use VDU1,255 for upwards &
VDU1,254 for downwards.
To `grey' the current window, which produces the effect seen when using a
pop-down such as the calculator, use VDU1,50,71,43 - grey ON and
VDU1,50,71,45 - grey OFF.
Multiple `Beeps'
The following sequence of codes rings the Z88's bell a number of times -
VDU1, 52, 33, 32+n, 32+w, 32+l where n is the number of beeps
w is the time between beeps in
10 msec units
l is the length of each beep in
10 msec units.
For example:- VDU1,52,33,36,132,232 will produce 4 beeps, each 2 secs
long (200+32) with a wait time of 1 sec (100+32) between them. A word of
warning: if you set the number of beeps to less than 0 the Z88 will
continue the sequence forever, necessitating a Soft Reset.
END
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