S.D.O (star defense operation)

Fast vertical shoot’em up for Amstrad CPC ,MSX and ZX Spectrum 48k, smooth action, arcade flow.

They’re closing in. Clear the skies, survive the waves, and push for the top of the table.

SDO started life as a game designed specifically for the Amstrad CPC, built around Mode 0 visuals, double buffering, frame pacing, and the feel of fast arcade action on 4 MHz hardware.

After the positive feedback from the original CPC release, the project gradually evolved into full adaptations for MSX1 and ZX Spectrum. Rather than aiming for identical conversions, each version was visually and technically reworked to better match the strengths, style, and personality of its hardware while preserving the core arcade gameplay of the original release.

The result is three distinct 8-bit versions of the same arcade shooter, each with its own visual identity and technical approach.

Amstrad CPC

• Arcade-style vertical shooter designed around CPC Mode 0 graphics
• Double-buffered rendering and frame-paced gameplay
• Fast scrolling with parallax starfield
• Original reference version of the project

MSX1 

• Graphics and enemies redesigned around MSX1 hardware sprites
• Multiple hardware sprites combined for larger and more colourful visuals
• Reworked screen layout and HUD adapted to the MSX VDP
• Gameplay and rendering rebalanced specifically for the MSX architecture

ZX Spectrum 48K 

• Full visual redesign tailored to the Spectrum’s distinctive visual style
• Custom Z80 ASM sprite blitter
• Optimised 50 Hz gameplay on unexpanded 48K hardware
• Reworked collision, starfield, and sound systems adapted specifically for the machine

Features

• 25 levels with a boss every 5 stages
• High-score focused arcade gameplay
• Joystick or keyboard controls
• Optional key redefinition
• Attract mode cycling title, scores, and help screens 
• Playable on real hardware or emulators

Who it’s for

For retro players, CPC, MSX and Spectrum enthusiasts, and anyone who enjoys fast arcade gameplay, short sessions, and chasing high scores the old-school way.

Development notes

SDO would not have been possible without CPCtelera, z88dk, RGAS, ConvImgCpc, GIMP,Arkos Tracker, MSXgl, Z88dk ,spriteSXdevtool, RVM and  Openmsx.

Now that all three versions are finally complete, I’ll probably take a short break to revisit and rethink an older unfinished project that has been sitting around for quite some time.

That said, if the Spectrum version receives enough interest, I’d love to explore a future 128K edition featuring AY sound, double buffering for even smoother gameplay, and the complete attract mode from the original CPC release.

Bug reports, feedback, gameplay suggestions, or improvement ideas are always welcome.

Loading instructions

CPC: run"disc

MSX: Insert rom

Spectrum: load"" and play on tape