Fixing Star Defence

Discussion, Reviews & High-scores

Moderator: Moderators

Post Reply
User avatar
GreyGhost
Vic 20 Nerd
Posts: 525
Joined: Wed Oct 05, 2005 11:10 pm

Fixing Star Defence

Post by GreyGhost »

Does anyone know of a working version of this game? The copy I have and the one in Gamebase stores values at $a000 and $a001 and then falls into an endless loop at $1a2e. I'm sure this is some sort of copy protection but I can't seem to follow the code to see a work around.

Code: Select all

.C:1a1c  FF FE FF    ISB $FFFE,X
.C:1a1f  FF A9 08    ISB $08A9,X
.C:1a22  8D 0F 90    STA $900F
.C:1a25  20 AD 1E    JSR $1EAD
.C:1a28  20 9A 1C    JSR $1C9A
.C:1a2b  20 2D 1D    JSR $1D2D
.C:1a2e  4C 2E 1A    JMP $1A2E
.C:1a31  A9 20       LDA #$20
.C:1a33  8D 00 A0    STA $A000
.C:1a36  A9 1A       LDA #$1A
.C:1a38  8D 01 A0    STA $A001
.C:1a3b  4C 20 1A    JMP $1A20
Rob
User avatar
mrr19121970
Vic 20 Nerd
Posts: 873
Joined: Tue Jan 19, 2016 9:22 am
Location: Germany
Occupation: IT service manager

Re: Fixing Star Defence

Post by mrr19121970 »

I don't know this game, but why don't you set the memory to read only ? K3ys expander has this to bypass such protection
User avatar
Mike
Herr VC
Posts: 4816
Joined: Wed Dec 01, 2004 1:57 pm
Location: Munich, Germany
Occupation: electrical engineer

Re: Fixing Star Defence

Post by Mike »

Have you tried pressing [f1] to start the game?

Actually, there's nothing dubious about the code. The game just thwarts soft-loaded (monitor?) cartridges by redirecting the reset vector of their auto-boot signature to its own init code. This init code sets up an interrupt for the whole game main loop, which first waits for [f1] and then runs the game. The foreground process then idles in $1a2e.

So, nothing's to fix here. ;)

P.S. the game is effectively PAL only as it uses an overscan screen that wouldn't fit on NTSC.
User avatar
GreyGhost
Vic 20 Nerd
Posts: 525
Joined: Wed Oct 05, 2005 11:10 pm

Re: Fixing Star Defence

Post by GreyGhost »

Mike wrote:Have you tried pressing [f1] to start the game?
*face palm* No, didn't try that one. Thanks Guys.
Rob
paradroid90
Vic 20 Newbie
Posts: 18
Joined: Thu Dec 06, 2012 3:28 pm
Location: Chatham Kent

Re: Fixing Star Defence

Post by paradroid90 »

Great Game though :-)
3583 Basic Bytes Free ;-)
Vic20-Ian
Vic 20 Scientist
Posts: 1213
Joined: Sun Aug 24, 2008 1:58 pm

Re: Fixing Star Defence

Post by Vic20-Ian »

Old Thread but if you try this game be sure to try the 2 game modes.

Function keys control 1 or 2 player and slow or fast game

From memory I think F5 toggles the game speed - it plays a tone but does not say slow of fast mode on screen.

High speed is frenetic. Good Scrolling and lovely laser effects.

A great version of Stargate / Defender.

Save 4 people and go through the stargate to warp to higher levels.

Destroy all the humans to blow up the planet until you survive 4 waves of mutants.

Smart bomb on Return and Invisible mode on Shift. Hyperspace (often kills you) on Spacebar and Radar on F3
Last edited by Vic20-Ian on Fri Jan 29, 2021 12:31 pm, edited 1 time in total.
Vic20-Ian

The best things in life are Vic-20

Upgrade all new gadgets and mobiles to 3583 Bytes Free today! Ready
hasseapa
Vic 20 Devotee
Posts: 264
Joined: Thu Oct 12, 2006 4:09 am

Re: Fixing Star Defence

Post by hasseapa »

As far as I remember this is the most playable Defender clone for Vic. I am partial to Jeff Minter's Defenda (aka Agressor) as I got it for Christmas, but Star Defence is better. I especially like the scaling of the small player ship and the big enemies (the opposite of Defenda) and as you say, the explosions are very satisfying.

The ground/mountains could look better and smoother scrolling would obviously also be an improvement.
Vic20-Ian
Vic 20 Scientist
Posts: 1213
Joined: Sun Aug 24, 2008 1:58 pm

Re: Fixing Star Defence

Post by Vic20-Ian »

I think it scrolls pretty good especially on fast mode.

I would like a life poke / trainer for this game to explore the levels.

Yllabian Dogfight is wave 5 - just white spaceships.

Firebomber Showdown - empty wave ?! on wave 10.

I never got to Wave 15...Wonder who shows up ?
Vic20-Ian

The best things in life are Vic-20

Upgrade all new gadgets and mobiles to 3583 Bytes Free today! Ready
hasseapa
Vic 20 Devotee
Posts: 264
Joined: Thu Oct 12, 2006 4:09 am

Re: Fixing Star Defence

Post by hasseapa »

It's been ages since I played it but it does sound very attractive from your description of the levels. I will fire it up on emulator when I have the time - hopefully soon.
Vic20-Ian
Vic 20 Scientist
Posts: 1213
Joined: Sun Aug 24, 2008 1:58 pm

Re: Fixing Star Defence

Post by Vic20-Ian »

hasseapa wrote: Mon Feb 11, 2019 4:38 pm It's been ages since I played it but it does sound very attractive from your description of the levels. I will fire it up on emulator when I have the time - hopefully soon.
There is a trained version now and you can see extra levels named every 5 waves.
Vic20-Ian

The best things in life are Vic-20

Upgrade all new gadgets and mobiles to 3583 Bytes Free today! Ready
Post Reply