ASTRO BLASTA (aka. Astro Blaster)
by J. Hall
from Games Computing, December 1984


Three waves of aliens try to break through Earth's defences, namely
your FX-III laser launcher. Unfortunately you have limited laser
power and using it too much will cause you to overheat and blow up.
If the attacking alien reaches your end it's also curtains.

On destroying the present wave of aliens you have chance to go onto
the next screen.

Your ship flies from right to left. Pressing fire (M) drops a bomb,
hopefully on the alien; missing causes you to go back to the beginning
of the wave. If the aliens fail to break through your barrier they
will mount the attack again from the beginning. Watch out, aliens
fire lasers.

Control keys:
Q = up
A = down
M = fire laser / drop bomb

10 aliens have to be destroyed on the first wave, 20 on the second
and 30 on the third.


RUNdown

Lines      Action

2-9        prints title and plays tune
15-25      prints your ship
30-40      reads direction keys (Q and A)
50         checks to see if you've pressed fire (M)
500-600    fires laser
800-820    prints initial score, lives left, etc.
1000-1200  moves alien
1500-1550  fires alien laser
2000-2040  this routine is called when the alien reaches your side
           of the screen
3000-3050  ship blows up routine
6000-6100  alien blows up routine
7000-7100  prints your ship
8000-8060  drops bomb
8500-8700  blows up alien, moves on one level
9000-9010  DATA for title tune
9500-9600  blows up your ship
9800-9940  sets up graphics


Variables Used

A,B        your ship's co-ordinates
X,Y        alien's co-ordinates
SC         score
HS         hi-score
AL         aliens destroyed
BL         lasers left
PIT,DUR    pitch & duration of notes in tune
PO         used in scoring
G,VAL      used in initialisation of graphics
E$         alien