Christian Forstreuter, known as vossi1, has introduced the LC256, a 4MHz 65c02-based computer featuring the Yamaha V9958 (V9938) graphics chip. Released under a Creative Commons Attribution-ShareAlike 4.0 International License, this system brings expanded capabilities while maintaining compatibility with classic hardware configurations.
Features
- 4MHz 65c02 processor
- 1MB RAM (256KB and 512KB options available)
- 32KB ROM with kernal and Basic 4+, including graphics commands
- 128KB dedicated video RAM
- IEC interface for peripheral connections
- Built-in IEC2SD drive
- RGB, YC, and composite video output supporting PAL and NTSC
- Two internal expansion slots
- External cartridge connector for development use
- Optional DAC/OPL3 sound card
- Optional HD63c09 CPU adapter
- Designed to fit in a Commodore 64 case with a C64 keyboard
Technical Details
The LC256 operates with a 4MHz PLCC CMD/Rockwell 65c02 CPU and CMD/Rockwell 65c22 or WDC 65c22 interface chips. Using a WDC 65C02S requires adjustments to solder pads JW1-4 and adding R62. For a WDC 65c22s, a resistor pack patch is needed on the board’s reverse side.
A recommended CPLD for the system is the EPM7064SLC44, though a 7032 model can be used with adapted code. A GAL 26CV12 is also an option with some DMA limitations and solder pad modifications. The VIA restore circuit from the VIC-20 can replace the NE555 circuit.
For RAM configurations, IC23 is required for 256KB and 512KB chips, while 128KB setups can use D1-4/R25,26 instead. The 8MHz oscillator serves both the CPU and the SD2IEC system. CPU clock speeds of 1, 2, and 4MHz are selectable, with a specially assembled ROM required for IEC timing at lower speeds. An additional oscillator (OSC2) allows for custom clock frequencies, including support for the 63c09 CPU.
PAL or NTSC selection is controlled via jumpers JP16-18. The SD2IEC requires an 8MHz, 3.3V oscillator.
Display and BASIC Compatibility
The LC256 supports two screen modes:
- 256×212 resolution, 40-column text mode, 256 fixed RGB colors
- 512×212 resolution, 80-column text mode, 16-color palette
The included BASIC interpreter is largely compatible with C64, PET, and CBM-II systems, except for certain PEEK and POKE memory access commands.
For more details and technical documentation, visit Christian’s LC256 GitHub repository: https://github.com/vossi1/lc256-computer
