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A project log for HBC-56: 65C02 + TMS9918A on a backplane

HBC-56 A homebrew 8-bit computer with a backplane. Initially with a 65C02 CPU card, a TMS9918A VDP and dual AY-3-8910 audio.

Troy SchrapelTroy Schrapel 08/19/2021 at 04:300 Comments

Started work on an Invaders clone in 6502 assembly. Heavily inspired by the classic TI Invaders. Fitting since it uses the same VDP (TMS9918A).

My 6502 is currently running at 4MHz which leaves plenty of time in the VSYNC blanking area to update the display. Responding the the sync interrupt of the TMS9918A.

Running in the VDP's Graphics I mode. Everything on the screen except for the player ships and the bullets are text glyphs. The player ships and bullets are hardware sprites. The reason being the TMS9918A only supports 4 sprites on a scanline. Because of this, I can't use the hardware sprite collision detection, so will need to roll my own.  Currently only tile-level collisions are implemented, but I will get to adding pixel-level collisions soon.

Work remaining:

All source code for the game in its current state is available: https://github.com/visrealm/hbc-56

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