HBC-56

A homebrew 8-bit computer on a (56 pin) 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 regular character LCD and 12864B graphics LCD)
• TMS9918A display card (composite output)
• Dual AY-3-8910 sound card
• PS/2 keyboard and dual NES controller card

All source code and schematics are available in this repository.

The hand-wired cards are currently being replaced by custom PCB's thanks to the support of PCBWay.

See schematics/6502 for the first example.

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: github.com/visrealm/vrEmuTms9918
• Support for the dual AY-3-8910 audio, keyboard and NES controller.

The emulator is also available for Web (Beta). HBC-56 Emulator Online

Full details on the Emulator and source code here: emulator

Running the demos

There are several ways to build ad run the demos. They are set up with makefiles, so it is preferred to have MAKE installed and in your PATH environment variable.

VSCode

1. Open the code/6502 directory in VSCode
2. For each test/demo program (eg. basic, invaders, tests\tms, tests\sfx, etc.) navigate to the .asm file and hit <Ctrl>+<F5>. This will build and run the program in the emulator. <Ctrl>+<Shift>+<B> to just build the ROM image without running.

Command-line (MAKE)

For each path (basic, invaders, tests/tms,tests/sfx):

1. Open a console to the path
2. 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/inp
make kbtest

Manually building a demo (without MAKE)

Example: invaders

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

Manually running a demo (without MAKE)

Example: invaders

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

Example: basic

cd code\6502\basic
..\..\..\emulator\bin\Hbc56Emu.exe --rom basic_tms.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

Thanks

Thanks to PCBWay for supporting this project.

Videos

License

This code is licensed under the MIT license