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CALLM N, [V], which calls a
machine language routine located at N.
If the second parameter is included in a
CALLM statement, then the HL register
pair will contain the address of variable
V. Upon return all 8080 registers and
flags are restored to their original state;
A = INP (#N) reads a byte off the
Nth Port into A;
OUT WN, A puts A into Port N;
A = PDL (I) sets A to the position of
the Ith paddle potentiometer;
UT calls the machine language monitor;
CHECK scans a cassette tape (or
disk) and examines all files to see if
their checksums are correct;
LOADA loads an array (or machine
language program stored as an array);
SAVEA saves an array on cassette (or
disk);
STEP allows single-stepping through
a Basic program;
A = VARPTR(B) variabie A is set to
the address of B;
HEX$(I) returns a string of
characters representing the hex value
of the number I;
LOGT(X) calculates the logarithm
base 10 of X;
RND(X) for which the user has the
choice of a hardware or software
generated random number.
Typing EDIT does not have the same
effect as in Microsoft Basic. Rather,
EDIT calls the editor, loads the current
program into it and displays the first 24
lines of text. Once in the editor, a
program can be easily altered by either
moving the cursor (using the cursor
keys) around to the appropriate place
and retyping or by moving the text
around (shift and cursor keys) and
retyping. Up to 255 characters may be
stored in a line and viewed by 'panning'
the screen. Carriage returns are visible
within the editor. If only a few lines are
required then the editor can be called
with EDIT N-M, EDIT N, EDIT N-
or EDIT -N. The editor is very easy to use
and can be left by pressing BREAK,
followed by space (to keep the changes)
or BREAK, BREAK if the edit is to be
disregarded. I found the editor
convenient and very easy to use.
DAI Basic is 'semi-compiling'
after each line is typed in, it is
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translated into an intermediate code
that is faster to execute than the Basic
statement typed in. Usually a 'semi-
compiling' Basic will not accept a line if
it contains errors since it cannot
translate it into intermediate code. This
can be quite irritating if you have to
type a long line again because of a silly
typing error but DAI Basic has got
around this problem. When an incorrect
line is typed in, an error message
immediately appears. When the program
is listed, the erroneous line is there but
has *** in front of it. These can be
easily edited out when the line is
corrected in the editor.
Every effort has been made in DAI
Basic to help the user debug a program
easily. As well as the debugging state-
ments STEP, TRON, TROFF and the
listing of error lines with ***, there are
25 distinct error messages. These are
more helpful than the usual SYNTAX
ERROR and are in English (eg
COLOUR NOT AVAILABLE IN LINE
200).
Graphics
The DAI personal computer has three
graphics definitions available (low,
medium and high resolution) as well as
an all character mode. The character
mode displays 60 by 24 characters. The
graphics definitions are: low - 65 x 88
pixels; medium - 130 x 176 pixels; high
- 260 x 352 pixels.
At each level of definition the user
has the choice of all graphics or four
lines of text on the bottom. If an
executing program uses a graphics only
mode and the user breaks in, the DAI
will move the picture up, switching into
graphics and text mode. On typing
CONT the picture rolls back down and
the program continues.
The graphics takes up user RAM (see
memory map) so you need at least
32k to use the high resolution graphics.
The DAI provides 16 colours; if all of
these were usable without restrictions,
far too much of the user RAM would be
occupied with the screen image. Instead,
DAI has two modes, a full-colour mode
and a restricted 16-colour mode for
each graphics definition. In four-colour
mode the user choses four colours out
of the 16 available (which can be
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changed at will, and the existing picture
changes colour immediately) and can
use any of these colours anywhere on
the screen. In a 16-colour mode, the
screen is divided into vertical fields 8
pixels arrows. Within each field only two
colours can he used.
A demonstration program was
provided with the machine that
followerl a plan. through a full 24
hours. It started with a crescent moon
in the left hand corner on a dark blue
screen. As time went by, first stars came
out and then the sky faded into light
blue. After the horizon became visible
the (perfectly round) sun slowly rose.
When it was high in the sky a Dutch
flag was raised on a flagpole. This was
followed by the playing of the Dutch
national anthem, When this was
completed, clouds passed across the
screen and night descended.
The colours were clear and the
resolution seemed fine. The graphics
can be accessed through machine code
or by the following commands in Basic:
COLORG A B C D for graphics
mode - this sets up the four colours
to be used in four colour mode.
COLORT A B 0 0 for text - this
sets up A as the background colour and
B as the character colour,
DOT X, Y, A. This places a pixel of
colour A at point X, Y.
DRAW X1, Y1 X2, Y2 A. This draws
a line of colour A between X1, Y1 and
X2, Y2.
FILL X1, Yl X2, Y2 A. This fills a
rectangle with opposite corners at X1,
Yl and X2, Y2 with colour A,
XMAX. The maximum allowable X
value for the current graphic mode.
YMAX. The maximum allowable Y
value for the current graphics mode.
SCRN(X, Y). The colour coordinates
X, Y.
CURSOR X, Y. In text mode this
moves the cursor to the Xth character
in the Yth line from the bottom of the
screen.
CURX. The Xth coordinate of the
cursor.
CURY. The Yth coordinate of the
cursor.
I found the graphics easy to use and
impressive. My criticisms are twofold.
Firstly, I'd like to see a set of sub-
routines for drawing characters in
graphics modes (graphs do improve with
labeis on their axes), and it would be
nice (especially with the 48k machine)
for there to be low and medium
resolution modes that allow the use of
16 colours anywhere on the screen.
Sound
The DAI can generate sound using three
independent programmable oscillators
and a random noise generator. Each of
the oscillator channels can be
programmed to produce sound in the
frequency range 30 Hz to 1 MHz at
whatever amplitude is required. The
noise generator which produces random
frequencies is designed to simulate
white noise and to provide a random
sequence for random numbers.
Oscillator channels one and two are
used to produce sounrl for the left
stereo output while channels two and
three are used for the right stereo
output.
A music program 'Music Tutor' came
with the review machine. When run,
staves appeared on the screen and the
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