PicoZ80 – Drop-In Z80 Replacement

Summary

picoZ80 Overview The picoZ80 continues the tranZPUter theme, replacing a physical Z80 in a host or industrial computer with a faster CPU, more memory, virtual devices, networking (WiFi, BT), rapid application loading from SD card and WiFi management. It is a custom PCB designed to drop directly into the Z80 DIP-40 CPU socket of any legacy Z80-based computer. Rather than using a discrete Z80 processor, the board hosts an RP2350B microcontroller — a dual-core 150MHz Cortex-M33 device capable of running at up to 300MHz — whose programmable I/O (PIO) state machines take full, cycle-accurate control of the Z80 address, data, and control buses. The picoZ80 is not a simple emulator adapter. Every bus transaction is handled in real time by the RP2350's PIO engines, giving the host system exactly the same bus timing it would see from a real Z80. At the same time, the RP2350's second core and abundant on-chip SRAM, combined with 8MB of external PSRAM and 16MB of Flash, allow an almost unlimited range of capabilities to be layered on top of the raw Z80 interface — including accelerated execution, virtualised memory, ROM banking, virtual disk drives, and full machine-persona emulation. An ESP32 co-processor provides WiFi and Bluetooth connectivity, SD-card mass storage, and a browser-based management interface. All configuration is driven from a single human-readable config.json file stored on the SD card, meaning no recompilation is required to reconfigure the board's memory map, ROM images, or driver selection. The picoZ80 has been demonstrated running within multiple Sharp MZ machines. A set of personas are being developed for these machines, indeed for other Z80 systems in time, to provide much needed features, such as banked RAM/ROM, floppy disk emulation, QuickDisk emulation, ROM Filing System, TranZPUter Filing System, all capable of being functional simultaneously. The configuration is entirely JSON-driven, adding support for a new Z80-based host is a matter of editing ...