Objective
Define a safe electrical architecture for bridging the Commodore 64 User Port to modern 3.3-volt microcontroller hardware and SD-based storage.
Design decision
The current interface direction uses SN74LVC244A and SN74HCT244 devices for level translation between the C64 and Raspberry Pi Pico sides of the system.
The design also treats the C64 User Port power budget as a hard constraint: the available +5 V supply is limited to 100 mA, so power protection and isolation are part of the interface architecture rather than an afterthought.
Result
HollowCore now has a defined electrical foundation for the User Port interface, Pico controller, and SD-storage path, with voltage compatibility and power constraints explicitly represented in the design.
Next
Continue electrical and interface development from this architecture and validate the design as hardware moves from planning into implementation.