cbmeeks / hbc-56

Homebrew 8-bit Backplane Computer

Troy's HBC-56

My Homebrew 8-bit Computer

A homebrew 8-bit computer with a backplane. Initially supporting the 6502 CPU, TMS9918A VDP and Dual AY-3-8910 PSG's. With plans to add support for Z80 and perhaps other CPUs in the future.

Current cards:

• 6502 CPU card
• Triple-mode clock card (based on James Sharman's design)
• RAM/ROM card (32KB of each)
• LCD display card (supports regulat character LCD and 12864B graphics LCD)
• TMS9918A display card (composite output)
• Dual AY-3-8910 sound card

Current breadboard circuits:

• NES controller
• PS/2 keyboard controller

All source code and schematics are available in this repository.

Emulator

I have also included an emulator for this system. The emulator supports:

• Realtime execution of code (at 4MHz).
• Step through disassembled code with labels.
• Examine CPU and VDP registers, RAM and VRAM.
• Full support for all TMS9918A display modes. See my TMS9918 emulator here: https://github.com/visrealm/vrEmuTms9918
• Support for the dual AY-3-8910 audio.

The emulator is also available for Web (Beta). You can try a live instance here: https://visrealm.github.io/hbc-56/emulator/wasm You can load a new ROM by dragging the rom file on to the emulator.

Full details on the Emulator here: github.com/visrealm/hbc-56/emulator

Running the demos

1. Ensure MAKE is available on your system and in your PATH
2. Ensure ACME assembler is in your PATH
3. For each path (basic, invaders, tests\tms, tests\sfx):

• Open a console to the path
• Type make (this will build the default program and run it in the emulator:

• Type make all to build and run all demos in the directory
• Type make <basefile> (filename without extension) to build and run a specific demo eg:

cd code\6502\tests\tms
make tms9918gfx2test

Manually building a demo

Example: invaders

cd code\6502\invaders
acme -I ..\lib -I ..\kernel -o invaders.o -l invaders.o.lmap invaders.asm

Manually running a demo

Example: invaders

cd code\6502\invaders
..\..\..\emulator\bin\Hbc56Emu.exe --rom invaders.o

Example: basic

cd code\6502\basic
..\..\..\emulator\bin\Hbc56Emu.exe --keyboard --rom hbc56_mon.o

Memory map

THe HBC-56 has 64KB addressable memory divided into RAM, ROM and IO as follows:

From	To	Purpose
$0000	$7eff	RAM
$7f00	$7fff	I/O
$8000	$ffff	ROM

The RAM and ROM is further divided by the HBC-56 Kernel:

From	To	Size	Purpose
$0000	$00ff	256 bytes	Zero page
$0100	$01ff	256 bytes	Stack
$0200	$79ff	30 kilobytes	User RAM
$7a00	$7eff	1280 bytes	Kernel RAM
$7f00	$7fff	256 bytes	I/O
$8000	$dfff	24 kilobytes	User ROM
$e000	$ffff	8 kilobytes	Kernel ROM

Videos

License

This code is licensed under the MIT license