PCB Multi Expander Board for Commodore C16, C116, and Plus/4

Plus4MultiExpander — Expansion Port Multiplier for Commodore 16 / 116 / Plus/4

The expansion board allows simultaneous connection of multiple cartridges/extensions to a single Expansion port in Commodore 264 family computers (C16, C116, Plus/4). It addresses a long-standing issue with these machines: the original 50-pin connector with a 2.00 mm pitch is practically unobtainable today. Plus4MultiExpander replaces it with a widely available 44-pin connector with a 2.54 mm pitch (like in the C64), enabling new extension projects to be built using easily accessible components.

Key Features:

• 3 expansion slots on a single board with maximum dimensions of 10×10 cm, in the standard cartridge spacing.
• Built-in address bus buffering — compensates for the increased capacitance resulting from connecting multiple cards simultaneously.
• Passive audio mixer combining signals from multiple cards simultaneously (for a single active slot, it is recommended to install a 0 Ω resistor to maintain full volume).
• Integrated 74HCT08 chip combining /C2_LO and /C2_HI signals into a single /C2 — this saved pins despite transitioning to a smaller connector (a total of 6 signals were removed: 3 unused pins and /RAS and /CAS, unnecessary in modern projects).
• Mounting on M2 pillars (recommended height approx. 12 mm).
• Tested compatibility with extensions already ported to the 44-pin connector: OpenC16Cart, PlusVIA, ReSeed, SoundX, as well as (community-tested) TCBM2SD and C264 Magic Cart.

Important Warning from the Project Author:

Despite rearranging the signal order to a layout similar to the C64 (for added safety), pins 13, 8, and D may cause collisions — never insert a cartridge intended for the C64 into the expander, as this may damage the hardware.

Compatibility:

Commodore 16, Commodore 116, Commodore Plus/4. Note — the 44-pin connector is not backward compatible with old cartridges designed for the original 50-pin connector.

Project:

https://github.com/SukkoPera/Plus4MultiExpander/