By Mark Dudley — originally published in COMPUTE!’s Gazette Issue 2, August 1983
“Cylon Zap” is an arcade-style game for the 8K expanded VIC-20 and the Commodore 64. A space station in the center of the screen, which you must defend at all costs, is attacked continually by Cylon ships. You must shoot them before they dive (kamikaze-style) into the space station.
To defend against the Cylons, you have two weapons. First, the joystick is moved up, down, right, or left to fire lasers in any of these four directions. Second, the fire button detonates a “smart bomb,” which immediately clears the screen of all visible attackers. Smart bombs should be used sparingly, for there are only three available at the beginning of play.
The score and the number of remaining bombs are continually updated at the upper-left corner of the screen. When the score reaches 30, the flank attackers begin to increase speed. When your score reaches 50, the attackers from the top and bottom increase their speed. If your score exceeds 60, you win bonus smart bombs.
If your point total is a high score since the program was first loaded, you enter your initials with the joystick. Moving the stick right or left steps through the alphabet forward or backward. When the correct letter is found, select it with the fire button. Be sure not to hold the fire button down too long when selecting your initials, or you may inadvertently choose the wrong letters.
The VIC-20 version of Cylon Zap is in three parts. The first part redefines the start of BASIC to allow room for the redefined character set. It also loads the second part, which puts the special characters into memory and prints instructions. The third part contains the game itself. Each part must be typed in separately and then saved to tape. When saved in sequence, the game will load smoothly. If you use a disk drive, you must load the second and third programs manually when the prompt “Press Play On Tape” appears on the screen.
The Commodore 64 version of Cylon Zap consists of only one section because of the 64’s larger memory. Otherwise, the game is essentially the same.
Breakdown Of The VIC Version
Here are brief explanations of what’s going on in the VIC version of Cylon Zap. This information is for programmers who are interested in studying the techniques used.
Program 1: Set-up (VIC-20)
Sets the start of BASIC pointer.
Sets both end-of-memory pointers.
Sets beginning of BASIC to 0.
Prints “bytes free” message.
Puts LOAD command into keyboard buffer.
Program 2: Special Instructions (VIC-20)
30 Clear screen, set screen color, lowercase.
35 Display title.
40-70 Load characters.
75 Load machine language routine, ask for instructions.
90 POKE LOAD command into keyboard, clear screen.
95-125 DATA statements for characters.
130-160 Instructions.
165 RETURN to continue message.
170-180 Instructions, return to LOAD command.
190-230 Subroutine for “Hit RETURN To Cont” message.
235-290 Opening title.
300-310 Routine to move title across screen.
400-513 Routine to enter machine language.
Program 3: Cylon Zap (VIC-20)
35-50 Initialize variables.
55 Set screen color, clear screen, display high scores.
60 Set beginning of play variables.
65 Set character pointer.
70-80 Clear screen, draw base.
90 Print score, bases, bombs in upper-left corner.
150-225 Enemy ship appear, move, hit.
230 No bases left, display scores.
233 Score 50 or more, ships appear faster.
235 GOTO beginning of joystick routine.
240-315 Draw base.
320-340 Fire laser up.
345-365 Fire laser down.
370-390 Fire laser left.
395-415 Fire laser right.
420-465 Music for entering initials.
470-475 DATA for song.
480-525 Explosion for hit on enemy ship, add score.
530-580 Bonus base and bomb routine.
585-615 Base explodes.
620-650 If score is one of high scores, rearrange other scores.
655-685 Print high scores and to play again.
690-725 Base explode graphics.
730-815 Enter initials routine.
820-850 Print scores and title.
855-895 Smart bomb explosion and scoring.
900 Ship alarm sound.
905-925 Enter initials print routine.
See program listings on page 119.